diff --git a/CLAUDE.md b/CLAUDE.md
index 01a20e3..66f8cd7 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -6,7 +6,8 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 A deep-zoom fractal explorer (Rust + wgpu + egui + WGSL). It zooms past the
 ~10¹³× limit of plain `f64` using **perturbation theory**: one high-precision
-reference orbit is computed on the CPU (arbitrary precision via `dashu-float`),
+reference orbit is computed on the CPU (arbitrary precision via `bignum::Big`:
+`rug` natively, `malachite-float` on the web),
 and every pixel is rendered on the GPU as a cheap `f32` delta from it, with
 rebasing to avoid glitches. Plain `f32` deltas run out of exponent range
 once a pixel is ~2^-124 wide (~10³⁴× at 1080p), so from 2^-122 per pixel
@@ -22,6 +23,7 @@ storage buffers, which the fragment shader needs for the reference orbit).
 ```sh
 cargo run --release          # native, run (release matters: fractal math is hot)
 cargo test                   # reference-orbit math, share-link round-trip, WGSL validation
+cargo test --features wasm   # same, on the web build's malachite big-float backend
 cargo test --test shader_valid   # just the WGSL parse/validate tests (naga, no GPU needed)
 cargo clippy
 cargo fmt                    # rustfmt.toml just pins edition = "2024"
@@ -33,7 +35,7 @@ Web build (WebGPU):
 ```sh
 rustup target add wasm32-unknown-unknown
 cargo install wasm-bindgen-cli --version 0.2.128   # must match the wasm-bindgen crate version
-./build-web.sh                                     # -> ./dist
+./build-web.sh                                     # -> ./dist (builds with --features wasm)
 python3 -m http.server -d dist 8080
 ```
 
@@ -105,8 +107,19 @@ runs out), rebase: `e ← y_n − X_0`, restart the reference index at 0. This i
 what makes deep zoom cheap — one expensive high-precision orbit, then every
 pixel is a handful of `f32` complex multiplies.
 
-- `src/view.rs` — `ViewState`; center is arbitrary-precision `FBig` (`Big`
-  type alias). The pixel scale (`half_height`) is a `Scale`, an f64
+- `src/bignum/` — `Big`, the arbitrary-precision binary float, with one
+  backend per library behind the same inherent API + operators: `rug`
+  (GMP/MPFR, default, fastest, can't target wasm32) and `malachite-float`
+  (pure Rust, the `wasm` feature, required for the web build; a
+  `compile_error!` enforces it). Cargo features are additive, so rug is a
+  non-wasm32 target dependency and the backend is picked by
+  `cfg(feature = "wasm")`. Both follow the precision rule: a result has the
+  larger operand precision, rounded to nearest; shifts are exact. Malachite's
+  zero has no precision, so its wrapper stores `prec` alongside. Any new
+  `Big` operation must be added to both backends (`cargo test` and
+  `cargo test --features wasm` run the same tests on each).
+- `src/view.rs` — `ViewState`; center is arbitrary-precision `Big`
+  (re-exported as `view::Big`). The pixel scale (`half_height`) is a `Scale`, an f64
   mantissa with its own i32 exponent, so it goes past f64's ~1e-308. Never
   collapse it (or a center difference) to a plain `f64` on a path used at
   depth. Rescale first: `Scale::scaled_f64(k)`, or shift the `Big` by
@@ -131,10 +144,10 @@ pixel is a handful of `f32` complex multiplies.
   `f32` pairs — that's the reference orbit the GPU perturbs from. At
   precision ≤ `F64_MAX_PRECISION` (80 bits, i.e. shallow views) it takes a
   plain-`f64` fast path (`compute_reference_f64`), so each kind's formula
-  exists twice in this file (f64 + `FBig`) and both must stay in sync;
+  exists twice in this file (f64 + `Big`) and both must stay in sync;
   `f64_fast_path_matches_big` checks they agree. The result is a `RefOrbit`:
   `points` plus a parallel `exps`. A point below 2^-100 (only possible on the
-  `FBig` path) is stored as a normalized mantissa with its exponent in `exps`
+  `Big` path) is stored as a normalized mantissa with its exponent in `exps`
   (the true value is `points[n]·2^exps[n]`). That happens when the orbit
   passes near 0 at a deep minibrot. `has_scaled()` then forces the deep
   pipeline, the only one that reads `exps`. Requests are made with 1.5×
@@ -190,7 +203,7 @@ pixel is a handful of `f32` complex multiplies.
   are `advance_delta_kind`/`fprime_kind`; `advance_delta`/`fprime` wrap them
   to blend two kinds during the kind-switch morph (`u.morph_from`,
   `u.morph_w`: each step is `(1-w)·f_kind + w·f_from`, mirrored on the CPU by
-  the `morph` argument of `compute_reference`, in both its f64 and `FBig`
+  the `morph` argument of `compute_reference`, in both its f64 and `Big`
   paths). The blend only exists in pipelines built with the `MORPH` override
   (part of `PipelineKey`, on while `morph_w > 0`); those also skip periodicity
   detection and the cardioid bypass. App side: `KindMorph` in
diff --git a/Cargo.toml b/Cargo.toml
index 39bb4b6..966727c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,10 +7,12 @@ edition = "2024"
 default = ["gui"]
 # Windowed egui app. Without it only `--headless` rendering is built.
 gui = ["dep:eframe", "dep:egui"]
+# Pure-Rust big floats for the web build (`rug` needs GMP/MPFR, which can't
+# target wasm32). Required for wasm32, optional natively (to test that backend).
+wasm = ["dep:malachite-float", "dep:malachite-base"]
 
 [dependencies]
 bytemuck = { version = "1.25.2", features = ["derive"] }
-dashu-float = "0.6.0"
 eframe = { version = "0.36.2", default-features = false, features = ["wgpu", "default_fonts", "x11", "wayland", "accesskit"], optional = true }
 egui = { version = "0.36.2", optional = true }
 ecolor = { version = "0.36.2", features = ["bytemuck"] }
@@ -18,11 +20,14 @@ wgpu = "30.0.1"
 glam = "0.33.8"
 log = "0.4.34"
 png = "0.18.1"
+malachite-float = { version = "0.12", optional = true }
+malachite-base = { version = "0.12", optional = true }
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 env_logger = "0.11.11"
 clap = { version = "4.5.51", features = ["derive"] }
 pollster = "1.0.1"
+rug = { version = "1.30.0", default-features = false, features = ["float", "std"] }
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 futures-channel = { version = "0.3.34", default-features = false, features = ["alloc", "std"] }
@@ -39,7 +44,7 @@ opt-level = 3
 # codegen-units = 1
 debug = true
 
-# Dev: keep our own crate debuggable, but optimize dependencies (dashu, wgpu,
+# Dev: keep our own crate debuggable, but optimize dependencies (big floats, wgpu,
 # egui) so the explorer is actually interactive during development.
 [profile.dev]
 opt-level = 1
diff --git a/README.md b/README.md
index d43d712..76a5288 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,8 @@
 A fast, interactive deep-zoom fractal explorer — Mandelbrot and Julia sets —
 built with **Rust + wgpu + egui + WGSL**. It zooms far past the ~10¹³× limit of
 plain `f64` using **perturbation theory**: one high-precision reference orbit is
-computed on the CPU (arbitrary precision via `dashu-float`), and every pixel is
+computed on the CPU (arbitrary precision via `rug` natively, `malachite-float`
+on the web), and every pixel is
 rendered on the GPU as a cheap `f32` delta from it, with **rebasing** to avoid
 glitches. Runs natively (Vulkan/Metal/DX12) and in the browser (WebGPU).
 
@@ -27,6 +28,9 @@ The `f32` GPU tier reaches roughly **10³⁰× magnification** with sharp detail
 cargo run --release
 ```
 
+Native builds use `rug` (GMP/MPFR) for the reference orbit, which needs a C
+toolchain and `m4` (on Windows, MSYS2).
+
 ## Build & run — web (WebGPU)
 
 Requires the `wasm32-unknown-unknown` target and `wasm-bindgen-cli` (matching the
@@ -37,6 +41,7 @@ rustup target add wasm32-unknown-unknown
 cargo install wasm-bindgen-cli --version 0.2.128   # once
 
 ./build-web.sh                       # outputs ./dist (index.html, .js, .wasm)
+                                     # (builds with --features wasm: pure-Rust big floats)
 python3 -m http.server -d dist 8080  # serve over http
 ```
 
@@ -60,7 +65,8 @@ qualifies. Deploy by serving the `dist/` directory as static files.
 
 ## How it works
 
-- `src/view.rs` — view state. Center is arbitrary precision (`FBig`); the pixel
+- `src/view.rs` — view state. Center is arbitrary precision (`Big`, from
+  `src/bignum/`); the pixel
   scale stays `f64` (even at 10³⁰× it is ~10⁻³³, within `f64` range).
 - `src/fractal/reference.rs` — high-precision reference orbit `Z_{n+1}=Z_n²+C`.
 - `src/shaders/mandelbrot.wgsl` — per-pixel perturbation `e_{n+1}=2·Z_n·e_n+e_n²+δc`
@@ -84,6 +90,7 @@ reference computation to a Web Worker.
 
 ```sh
 cargo test
+cargo test --features wasm   # same suite on the web build's big-float backend
 ```
 
 Covers the reference orbit (vs. a naive `f64` iteration, Mandelbrot and Julia)
diff --git a/build-web.sh b/build-web.sh
index 87e8f82..8ac13e3 100755
--- a/build-web.sh
+++ b/build-web.sh
@@ -8,7 +8,7 @@ export PATH="$HOME/.cargo/bin:$PATH"
 OUT="${1:-dist}"
 
 echo "==> cargo build (wasm32, release)"
-cargo build --release --target wasm32-unknown-unknown
+cargo build --release --target wasm32-unknown-unknown --features wasm
 
 echo "==> wasm-bindgen -> $OUT"
 mkdir -p "$OUT"
diff --git a/src/app.rs b/src/app.rs
index 604b4e1..7395477 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -1144,12 +1144,8 @@ impl FractalApp {
     fn drift_from(&self, key: &RequestKey) -> f64 {
         let hh = self.view.half_height;
         let k = -hh.exponent() as isize;
-        let dre = ((&self.view.center_re - &key.center_re) << k)
-            .to_f64()
-            .value();
-        let dim = ((&self.view.center_im - &key.center_im) << k)
-            .to_f64()
-            .value();
+        let dre = ((&self.view.center_re - &key.center_re) << k).to_f64();
+        let dim = ((&self.view.center_im - &key.center_im) << k).to_f64();
         (dre * dre + dim * dim).sqrt() / hh.scaled_f64(-hh.exponent())
     }
 
@@ -1198,12 +1194,8 @@ impl FractalApp {
     /// underflow f64 at deep zooms).
     fn dc_offset(&self, scale_exp: i32) -> (f64, f64) {
         let k = -scale_exp as isize;
-        let dre = ((&self.view.center_re - &self.ref_center_re) << k)
-            .to_f64()
-            .value();
-        let dim = ((&self.view.center_im - &self.ref_center_im) << k)
-            .to_f64()
-            .value();
+        let dre = ((&self.view.center_re - &self.ref_center_re) << k).to_f64();
+        let dim = ((&self.view.center_im - &self.ref_center_im) << k).to_f64();
         (dre, dim)
     }
 
@@ -1494,8 +1486,8 @@ impl FractalApp {
     /// Buddhabrot mode doesn't support deep zoom (see `fractal::buddhabrot`).
     fn make_buddhabrot_uniforms(&self, aspect: f64) -> BuddhabrotUniforms {
         let center = [
-            self.view.center_re.to_f64().value() as f32,
-            self.view.center_im.to_f64().value() as f32,
+            self.view.center_re.to_f64() as f32,
+            self.view.center_im.to_f64() as f32,
         ];
         BuddhabrotUniforms {
             center,
diff --git a/src/bignum/mod.rs b/src/bignum/mod.rs
new file mode 100644
index 0000000..1ccc8ba
--- /dev/null
+++ b/src/bignum/mod.rs
@@ -0,0 +1,225 @@
+//! Arbitrary-precision binary float [`Big`] (one coordinate of a deep-zoom
+//! center, or of a reference orbit point), over one of two backends:
+//!
+//! - native (default): `rug` (GMP/MPFR), the fastest, but C code that can't
+//!   target `wasm32-unknown-unknown`;
+//! - `wasm` feature: a pure-Rust library, required for the web build.
+//!
+//! Both expose the same inherent API plus the operators below, and follow
+//! the same precision rule: an operation's result has the larger of its
+//! operands' precisions (in bits), rounded to nearest. Shifts (`<<`/`>>` by
+//! an `isize`) are exact multiplications by powers of two.
+
+#[cfg(not(feature = "wasm"))]
+mod rug_backend;
+#[cfg(not(feature = "wasm"))]
+pub use rug_backend::Big;
+
+#[cfg(feature = "wasm")]
+mod web_backend;
+#[cfg(feature = "wasm")]
+pub use web_backend::Big;
+// Native `--features wasm` builds (to test the web backend) still link rug.
+#[cfg(all(feature = "wasm", not(target_arch = "wasm32")))]
+use rug as _;
+
+#[cfg(all(target_arch = "wasm32", not(feature = "wasm")))]
+compile_error!("the web build needs `--features wasm` (rug can't target wasm32)");
+
+use core::ops::{Add, Mul, Neg, Shl, Shr, Sub};
+
+/// Implements `$Trait` for every owned/borrowed combination of `Big`
+/// operands, through the backend's by-reference `$imp`.
+macro_rules! forward_binop {
+    ($Trait:ident, $method:ident, $imp:ident) => {
+        impl $Trait<&Big> for &Big {
+            type Output = Big;
+            fn $method(self, rhs: &Big) -> Big {
+                self.$imp(rhs)
+            }
+        }
+        impl $Trait<Big> for &Big {
+            type Output = Big;
+            fn $method(self, rhs: Big) -> Big {
+                self.$imp(&rhs)
+            }
+        }
+        impl $Trait<&Big> for Big {
+            type Output = Big;
+            fn $method(self, rhs: &Big) -> Big {
+                (&self).$imp(rhs)
+            }
+        }
+        impl $Trait<Big> for Big {
+            type Output = Big;
+            fn $method(self, rhs: Big) -> Big {
+                (&self).$imp(&rhs)
+            }
+        }
+    };
+}
+
+forward_binop!(Add, add, add_ref);
+forward_binop!(Sub, sub, sub_ref);
+forward_binop!(Mul, mul, mul_ref);
+
+impl Neg for Big {
+    type Output = Big;
+    fn neg(self) -> Big {
+        self.negated()
+    }
+}
+
+impl Neg for &Big {
+    type Output = Big;
+    fn neg(self) -> Big {
+        self.clone().negated()
+    }
+}
+
+impl Shl<isize> for Big {
+    type Output = Big;
+    fn shl(self, k: isize) -> Big {
+        self.mul_pow2(k)
+    }
+}
+
+impl Shl<isize> for &Big {
+    type Output = Big;
+    fn shl(self, k: isize) -> Big {
+        self.clone().mul_pow2(k)
+    }
+}
+
+impl Shr<isize> for Big {
+    type Output = Big;
+    fn shr(self, k: isize) -> Big {
+        self.mul_pow2(-k)
+    }
+}
+
+impl Shr<isize> for &Big {
+    type Output = Big;
+    fn shr(self, k: isize) -> Big {
+        self.clone().mul_pow2(-k)
+    }
+}
+
+/// Significant decimal digits of a value, as a backend's
+/// `to_decimal_parts` returns them: the value is `±0.digits × 10^exp10`,
+/// `digits` has no trailing zeros, and it is empty for zero.
+pub struct DecimalParts {
+    pub negative: bool,
+    pub digits: String,
+    pub exp10: isize,
+}
+
+impl DecimalParts {
+    /// Build from a significand digit string (maybe with trailing zeros)
+    /// whose value is `0.digits × 10^exp10`.
+    fn new(negative: bool, digits: &str, exp10: isize) -> Self {
+        let digits = digits.trim_end_matches('0').to_string();
+        Self {
+            negative: negative && !digits.is_empty(),
+            digits,
+            exp10,
+        }
+    }
+}
+
+impl Big {
+    /// Decimal string with `sig_digits` significant digits, in plain
+    /// positional notation (`-0.000123`, `4500`), trailing zeros trimmed.
+    pub fn to_decimal_string(&self, sig_digits: usize) -> String {
+        let DecimalParts {
+            negative,
+            digits,
+            exp10,
+        } = self.to_decimal_parts(sig_digits.max(1));
+        if digits.is_empty() {
+            return "0".to_string();
+        }
+        let sign = if negative { "-" } else { "" };
+        let len = digits.len() as isize;
+        if exp10 <= 0 {
+            let zeros = "0".repeat((-exp10) as usize);
+            format!("{sign}0.{zeros}{digits}")
+        } else if exp10 >= len {
+            let zeros = "0".repeat((exp10 - len) as usize);
+            format!("{sign}{digits}{zeros}")
+        } else {
+            let (int, frac) = digits.split_at(exp10 as usize);
+            format!("{sign}{int}.{frac}")
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn big(x: f64) -> Big {
+        Big::from_f64(x, 200)
+    }
+
+    #[test]
+    fn decimal_string_is_positional() {
+        assert_eq!(
+            big(-0.7515).to_decimal_string(20),
+            "-0.75149999999999994582"
+        );
+        assert_eq!(big(-0.7515).to_decimal_string(5), "-0.7515");
+        assert_eq!(big(0.0).to_decimal_string(5), "0");
+        assert_eq!(big(1.0).to_decimal_string(5), "1");
+        assert_eq!(big(123.456).to_decimal_string(5), "123.46");
+        assert_eq!(big(1e20).to_decimal_string(5), "100000000000000000000");
+        assert_eq!(big(0.1).to_decimal_string(5), "0.1");
+        let tiny = big(1.0) >> 200;
+        let s = tiny.to_decimal_string(5);
+        assert_eq!(s, format!("0.{}6223", "0".repeat(60)));
+    }
+
+    #[test]
+    fn decimal_round_trip() {
+        let s = "-0.743643887037158704752191506114774";
+        let x = Big::from_decimal_str(s, 200).unwrap();
+        assert_eq!(x.to_decimal_string(33), s);
+        assert_eq!(
+            Big::from_decimal_str("1.5e-20", 64).unwrap().to_f64(),
+            1.5e-20
+        );
+        assert!(Big::from_decimal_str("abc", 64).is_none());
+    }
+
+    #[test]
+    fn precision_is_max_of_operands() {
+        let a = Big::from_f64(1.0, 100);
+        let b = Big::from_f64(3.0, 200);
+        assert_eq!((&a + &b).precision(), 200);
+        assert_eq!((&a * &b).precision(), 200);
+        assert_eq!((&b - &a).precision(), 200);
+        assert_eq!(a.clone().with_precision(300).precision(), 300);
+    }
+
+    #[test]
+    fn exact_shifts_and_log2() {
+        let x = Big::from_f64(0.75, 64) >> 5000;
+        assert_eq!(x.log2_floor(), Some(-5001));
+        assert_eq!((x << 5000).to_f64(), 0.75);
+        assert_eq!(Big::zero(64).log2_floor(), None);
+        assert!(Big::from_f64(-1.0, 64).is_negative());
+        assert!(!Big::zero(64).is_negative());
+    }
+
+    #[test]
+    fn transcendentals() {
+        let x = Big::from_f64(0.5, 128);
+        assert!((x.ln().to_f64() - 0.5f64.ln()).abs() < 1e-15);
+        assert!((x.exp().to_f64() - 0.5f64.exp()).abs() < 1e-15);
+        let (s, c) = x.sin_cos();
+        assert!((s.to_f64() - 0.5f64.sin()).abs() < 1e-15);
+        assert!((c.to_f64() - 0.5f64.cos()).abs() < 1e-15);
+        let y = Big::from_f64(-0.3, 128);
+        assert!((y.atan2(&x).to_f64() - (-0.3f64).atan2(0.5)).abs() < 1e-15);
+    }
+}
diff --git a/src/bignum/rug_backend.rs b/src/bignum/rug_backend.rs
new file mode 100644
index 0000000..bffe793
--- /dev/null
+++ b/src/bignum/rug_backend.rs
@@ -0,0 +1,128 @@
+//! [`Big`] over `rug::Float` (MPFR), for native builds.
+
+use core::cmp::Ordering;
+
+use rug::{Assign, Float};
+
+use super::DecimalParts;
+
+/// Arbitrary-precision binary float. See the module docs.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Big(Float);
+
+/// MPFR precision for `bits`, clamped to what it accepts.
+fn prec(bits: usize) -> u32 {
+    (bits as u32).clamp(rug::float::prec_min(), rug::float::prec_max())
+}
+
+impl Big {
+    /// `x` at `bits` of precision (exact when `bits >= 53`). Non-finite `x`
+    /// reads as 0.
+    pub fn from_f64(x: f64, bits: usize) -> Self {
+        let x = if x.is_finite() { x } else { 0.0 };
+        Self(Float::with_val(prec(bits), x))
+    }
+
+    pub fn zero(bits: usize) -> Self {
+        Self(Float::new(prec(bits)))
+    }
+
+    /// Parse a decimal (`-0.75`, `1.5e-20`, any number of digits) at `bits`
+    /// (at least 53) of precision.
+    pub fn from_decimal_str(s: &str, bits: usize) -> Option<Self> {
+        let parsed = Float::parse(s.trim()).ok()?;
+        let x = Float::with_val(prec(bits.max(53)), parsed);
+        x.is_finite().then_some(Self(x))
+    }
+
+    pub fn precision(&self) -> usize {
+        self.0.prec() as usize
+    }
+
+    /// Change the precision, rounding to nearest if it shrinks.
+    pub fn with_precision(mut self, bits: usize) -> Self {
+        self.0.set_prec(prec(bits));
+        self
+    }
+
+    pub fn to_f64(&self) -> f64 {
+        self.0.to_f64()
+    }
+
+    pub fn is_zero(&self) -> bool {
+        self.0.is_zero()
+    }
+
+    pub fn is_negative(&self) -> bool {
+        self.0.cmp0() == Some(Ordering::Less)
+    }
+
+    pub fn abs(self) -> Self {
+        Self(self.0.abs())
+    }
+
+    pub fn sqr(&self) -> Self {
+        Self(Float::with_val(self.0.prec(), self.0.square_ref()))
+    }
+
+    /// `floor(log2|x|)`, or `None` for zero. Exact, at any exponent.
+    pub fn log2_floor(&self) -> Option<isize> {
+        // MPFR normalizes the significand to [0.5, 1).
+        self.0.get_exp().map(|e| e as isize - 1)
+    }
+
+    pub fn ln(&self) -> Self {
+        Self(Float::with_val(self.0.prec(), self.0.ln_ref()))
+    }
+
+    pub fn exp(&self) -> Self {
+        Self(Float::with_val(self.0.prec(), self.0.exp_ref()))
+    }
+
+    /// `atan2(self, x)`: the angle of `(x, self)`.
+    pub fn atan2(&self, x: &Big) -> Self {
+        let p = self.0.prec().max(x.0.prec());
+        Self(Float::with_val(p, self.0.atan2_ref(&x.0)))
+    }
+
+    pub fn sin_cos(&self) -> (Self, Self) {
+        let p = self.0.prec();
+        let (mut s, mut c) = (Float::new(p), Float::new(p));
+        (&mut s, &mut c).assign(self.0.sin_cos_ref());
+        (Self(s), Self(c))
+    }
+
+    /// `sig` significant decimal digits (rounded to nearest).
+    pub fn to_decimal_parts(&self, sig: usize) -> DecimalParts {
+        if self.0.is_zero() {
+            return DecimalParts::new(false, "", 0);
+        }
+        let (negative, digits, exp) = self.0.to_sign_string_exp(10, Some(sig));
+        DecimalParts::new(negative, &digits, exp.unwrap_or(0) as isize)
+    }
+
+    pub(super) fn add_ref(&self, rhs: &Big) -> Big {
+        let p = self.0.prec().max(rhs.0.prec());
+        Big(Float::with_val(p, &self.0 + &rhs.0))
+    }
+
+    pub(super) fn sub_ref(&self, rhs: &Big) -> Big {
+        let p = self.0.prec().max(rhs.0.prec());
+        Big(Float::with_val(p, &self.0 - &rhs.0))
+    }
+
+    pub(super) fn mul_ref(&self, rhs: &Big) -> Big {
+        let p = self.0.prec().max(rhs.0.prec());
+        Big(Float::with_val(p, &self.0 * &rhs.0))
+    }
+
+    pub(super) fn negated(self) -> Big {
+        Big(-self.0)
+    }
+
+    /// `self · 2^k`, exact. `|k|` stays far below `i32::MAX` (precision and
+    /// zoom depth are capped around 2^20 bits).
+    pub(super) fn mul_pow2(self, k: isize) -> Big {
+        Big(self.0 << k as i32)
+    }
+}
diff --git a/src/bignum/web_backend.rs b/src/bignum/web_backend.rs
new file mode 100644
index 0000000..b86b403
--- /dev/null
+++ b/src/bignum/web_backend.rs
@@ -0,0 +1,173 @@
+//! [`Big`] over `malachite-float`, pure Rust, for the web build.
+
+use malachite_base::num::basic::traits::Zero;
+use malachite_base::num::conversion::string::options::ToSciOptions;
+use malachite_base::num::conversion::traits::{RoundingFrom, ToSci};
+use malachite_base::rounding_modes::RoundingMode::Nearest;
+use malachite_float::Float;
+
+use super::DecimalParts;
+
+/// Arbitrary-precision binary float. See the module docs.
+///
+/// The precision is stored next to the value: malachite's zero has none,
+/// but "zero at `p` bits" must still lift a sum with it to `p` bits.
+#[derive(Clone, Debug)]
+pub struct Big {
+    f: Float,
+    prec: u64,
+}
+
+impl PartialEq for Big {
+    fn eq(&self, other: &Self) -> bool {
+        self.f == other.f
+    }
+}
+
+fn prec(bits: usize) -> u64 {
+    (bits as u64).max(1)
+}
+
+impl Big {
+    fn new(f: Float, prec: u64) -> Self {
+        // Only finite values reach here; anything else (overflow) is a bug.
+        debug_assert!(f.is_finite(), "non-finite Big: {f}");
+        Self { f, prec }
+    }
+
+    /// `x` at `bits` of precision (exact when `bits >= 53`). Non-finite `x`
+    /// reads as 0.
+    pub fn from_f64(x: f64, bits: usize) -> Self {
+        let p = prec(bits);
+        if !x.is_finite() {
+            return Self::zero(bits);
+        }
+        Self::new(Float::from_primitive_float_prec(x, p).0, p)
+    }
+
+    pub fn zero(bits: usize) -> Self {
+        Self::new(Float::ZERO, prec(bits))
+    }
+
+    /// Parse a decimal (`-0.75`, `1.5e-20`, any number of digits) at `bits`
+    /// (at least 53) of precision.
+    pub fn from_decimal_str(s: &str, bits: usize) -> Option<Self> {
+        let p = prec(bits.max(53));
+        let (f, _) = Float::from_sci_string_prec(s.trim(), p)?;
+        f.is_finite().then(|| Self::new(f, p))
+    }
+
+    pub fn precision(&self) -> usize {
+        self.prec as usize
+    }
+
+    /// Change the precision, rounding to nearest if it shrinks.
+    pub fn with_precision(mut self, bits: usize) -> Self {
+        let p = prec(bits);
+        if self.f.get_prec().is_some() {
+            self.f.set_prec(p);
+        }
+        self.prec = p;
+        self
+    }
+
+    pub fn to_f64(&self) -> f64 {
+        f64::rounding_from(&self.f, Nearest).0
+    }
+
+    pub fn is_zero(&self) -> bool {
+        self.f.is_zero()
+    }
+
+    pub fn is_negative(&self) -> bool {
+        self.f.is_sign_negative() && !self.f.is_zero()
+    }
+
+    pub fn abs(self) -> Self {
+        if self.f.is_sign_negative() {
+            self.negated()
+        } else {
+            self
+        }
+    }
+
+    pub fn sqr(&self) -> Self {
+        Self::new(self.f.square_prec_ref(self.prec).0, self.prec)
+    }
+
+    /// `floor(log2|x|)`, or `None` for zero. Exact, at any exponent.
+    pub fn log2_floor(&self) -> Option<isize> {
+        // The significand is normalized to [0.5, 1).
+        self.f.get_exponent().map(|e| e as isize - 1)
+    }
+
+    pub fn ln(&self) -> Self {
+        Self::new(self.f.ln_prec_ref(self.prec).0, self.prec)
+    }
+
+    pub fn exp(&self) -> Self {
+        Self::new(self.f.exp_prec_ref(self.prec).0, self.prec)
+    }
+
+    /// `atan2(self, x)`: the angle of `(x, self)`.
+    pub fn atan2(&self, x: &Big) -> Self {
+        let p = self.prec.max(x.prec);
+        Self::new(self.f.atan2_prec_ref_ref(&x.f, p).0, p)
+    }
+
+    pub fn sin_cos(&self) -> (Self, Self) {
+        let (s, c, _, _) = self.f.sin_cos_prec_ref(self.prec);
+        (Self::new(s, self.prec), Self::new(c, self.prec))
+    }
+
+    /// `sig` significant decimal digits (rounded to nearest).
+    pub fn to_decimal_parts(&self, sig: usize) -> DecimalParts {
+        if self.f.is_zero() {
+            return DecimalParts::new(false, "", 0);
+        }
+        let mut options = ToSciOptions::default();
+        options.set_precision(sig as u64);
+        let s = self.f.to_sci_with_options(options).to_string();
+        // `[-]int[.frac][e±N]`, positional or scientific depending on size.
+        let (negative, s) = match s.strip_prefix('-') {
+            Some(rest) => (true, rest),
+            None => (false, s.as_str()),
+        };
+        let (mantissa, exp) = match s.split_once(['e', 'E']) {
+            Some((m, e)) => (m, e.trim_start_matches('+').parse::<isize>().unwrap_or(0)),
+            None => (s, 0),
+        };
+        let (int, frac) = mantissa.split_once('.').unwrap_or((mantissa, ""));
+        let all = format!("{int}{frac}");
+        let digits = all.trim_start_matches('0');
+        let leading_zeros = (all.len() - digits.len()) as isize;
+        // 0.digits · 10^exp10 = int.frac · 10^exp.
+        let exp10 = int.len() as isize - leading_zeros + exp;
+        DecimalParts::new(negative, digits, exp10)
+    }
+
+    pub(super) fn add_ref(&self, rhs: &Big) -> Big {
+        let p = self.prec.max(rhs.prec);
+        Big::new(self.f.add_prec_ref_ref(&rhs.f, p).0, p)
+    }
+
+    pub(super) fn sub_ref(&self, rhs: &Big) -> Big {
+        let p = self.prec.max(rhs.prec);
+        Big::new(self.f.sub_prec_ref_ref(&rhs.f, p).0, p)
+    }
+
+    pub(super) fn mul_ref(&self, rhs: &Big) -> Big {
+        let p = self.prec.max(rhs.prec);
+        Big::new(self.f.mul_prec_ref_ref(&rhs.f, p).0, p)
+    }
+
+    pub(super) fn negated(self) -> Big {
+        Big::new(-self.f, self.prec)
+    }
+
+    /// `self · 2^k`, exact (malachite's exponent range is ±2^30, far past
+    /// what zoom depth needs).
+    pub(super) fn mul_pow2(self, k: isize) -> Big {
+        Big::new(self.f << k as i64, self.prec)
+    }
+}
diff --git a/src/fractal/reference.rs b/src/fractal/reference.rs
index 0bbe4fd..0d8be39 100644
--- a/src/fractal/reference.rs
+++ b/src/fractal/reference.rs
@@ -1,7 +1,7 @@
 //! High-precision reference-orbit computation for perturbation rendering.
 //!
 //! We iterate the fractal's formula `Z_{n+1} = f(Z_n, C)` at high precision
-//! (`dashu-float`), storing each `Z_n` as an `f32` pair. Every pixel is then
+//! ([`Big`]: `rug` natively, pure Rust on the web), storing each `Z_n` as an `f32` pair. Every pixel is then
 //! rendered on the GPU as a small `f32` delta from this orbit — that is what
 //! makes deep zoom cheap. See `shaders/mandelbrot.wgsl` for the delta side; the
 //! delta formula there must match the orbit formula here.
@@ -24,7 +24,7 @@ use crate::view::{Big, big_from_f64};
 const REFERENCE_ESCAPE_SQ: f64 = 1.0e10;
 
 /// Up to this working precision (bits) the orbit is iterated in plain `f64`
-/// instead of `FBig` — orders of magnitude faster, which matters most on the
+/// instead of `Big` — orders of magnitude faster, which matters most on the
 /// web (where the reference is computed inline on the UI thread).
 ///
 /// `precision_for` asks for `zoom_bits + 48` guard bits, but the GPU only
@@ -96,29 +96,21 @@ impl<'a> IntoIterator for &'a RefOrbit {
     }
 }
 
-/// `floor(log2|x|)`, or `None` for zero. Exact (from the binary
-/// representation), and works far below f64's range.
-fn big_log2_floor(x: &Big) -> Option<isize> {
-    let repr = x.repr();
-    let digits = repr.digits();
-    (digits > 0).then(|| repr.exponent() + digits as isize - 1)
-}
-
 /// Store `(zr, zi)` into `orbit`, as plain f32 unless its magnitude is below
 /// `2^TINY_LOG2`, in which case both components share an exponent `k` and
 /// the stored mantissa `Z * 2^-k` has its larger component in `[0.5, 1)`.
 fn push_big_point(orbit: &mut RefOrbit, zr: &Big, zi: &Big) {
-    let (lr, li) = (big_log2_floor(zr), big_log2_floor(zi));
+    let (lr, li) = (zr.log2_floor(), zi.log2_floor());
     let top = lr.max(li);
     match top {
         Some(top) if top < TINY_LOG2 as isize => {
             let k = top + 1;
-            let mr = (zr.clone() << -k).to_f64().value() as f32;
-            let mi = (zi.clone() << -k).to_f64().value() as f32;
+            let mr = (zr.clone() << -k).to_f64() as f32;
+            let mi = (zi.clone() << -k).to_f64() as f32;
             orbit.points.push([mr, mi]);
             orbit.exps.push(k as i32);
         }
-        _ => orbit.push([zr.to_f64().value() as f32, zi.to_f64().value() as f32]),
+        _ => orbit.push([zr.to_f64() as f32, zi.to_f64() as f32]),
     }
 }
 
@@ -147,23 +139,17 @@ pub fn compute_reference(
     let morph = morph.filter(|&(_, w)| w != 0.0);
     if precision <= F64_MAX_PRECISION {
         let k = StepConstsF64 {
-            c: (c_re.to_f64().value(), c_im.to_f64().value()),
+            c: (c_re.to_f64(), c_im.to_f64()),
             p: phoenix_p,
             l: lambda_l,
             cpow: complex_power,
             power,
         };
-        return compute_reference_f64(
-            (z0_re.to_f64().value(), z0_im.to_f64().value()),
-            max_iter,
-            kind,
-            &k,
-            morph,
-        );
+        return compute_reference_f64((z0_re.to_f64(), z0_im.to_f64()), max_iter, kind, &k, morph);
     }
     let k = StepConsts {
-        cr: c_re.clone().with_precision(precision).value(),
-        ci: c_im.clone().with_precision(precision).value(),
+        cr: c_re.clone().with_precision(precision),
+        ci: c_im.clone().with_precision(precision),
         pr: big_from_f64(phoenix_p.0, precision),
         pi: big_from_f64(phoenix_p.1, precision),
         lr: big_from_f64(lambda_l.0, precision),
@@ -292,7 +278,7 @@ struct StepConsts {
     precision: usize,
 }
 
-/// [`compute_reference`] at arbitrary precision (`FBig`), for deep views.
+/// [`compute_reference`] at arbitrary precision ([`Big`]), for deep views.
 fn compute_reference_big(
     z0_re: &Big,
     z0_im: &Big,
@@ -304,11 +290,11 @@ fn compute_reference_big(
     let precision = k.precision;
     let morph = morph.map(|(from, w)| (from, big_from_f64(w, precision)));
 
-    let mut zr = z0_re.clone().with_precision(precision).value();
-    let mut zi = z0_im.clone().with_precision(precision).value();
+    let mut zr = z0_re.clone().with_precision(precision);
+    let mut zi = z0_im.clone().with_precision(precision);
     // Previous iterate, for the Phoenix two-term recurrence (Y_{-1} = 0).
-    let mut zr_prev = big_zero(precision);
-    let mut zi_prev = big_zero(precision);
+    let mut zr_prev = Big::zero(precision);
+    let mut zi_prev = Big::zero(precision);
 
     let mut points = RefOrbit::with_capacity(max_iter as usize + 1);
 
@@ -332,8 +318,8 @@ fn compute_reference_big(
         // Shift the previous iterate (only the Phoenix arm reads it).
         zr_prev = zr;
         zi_prev = zi;
-        zr = new_zr.with_precision(precision).value();
-        zi = new_zi.with_precision(precision).value();
+        zr = new_zr.with_precision(precision);
+        zi = new_zi.with_precision(precision);
     }
 
     points
@@ -361,7 +347,7 @@ fn step(
         FractalKind::BurningShip => {
             // (|zr| + i|zi|)^2 = (zr^2 - zi^2) + 2|zr zi| i.
             let re = &zr.sqr() - &zi.sqr() + cr;
-            let im = big_abs((zr * zi) << 1) + ci;
+            let im = ((zr * zi) << 1).abs() + ci;
             (re, im)
         }
         FractalKind::Tricorn => {
@@ -376,14 +362,14 @@ fn step(
         }
         FractalKind::Celtic => {
             // |Re(z^2)| + i·Im(z^2): abs the real output of the square.
-            let re = big_abs(&zr.sqr() - &zi.sqr()) + cr;
+            let re = (&zr.sqr() - &zi.sqr()).abs() + cr;
             let im = ((zr * zi) << 1) + ci;
             (re, im)
         }
         FractalKind::Perpendicular => {
             // (x^2 - y^2) - 2·x·|y| i: abs the imaginary input.
             let re = &zr.sqr() - &zi.sqr() + cr;
-            let im = if *zi < Big::ZERO {
+            let im = if zi.is_negative() {
                 ci + ((zr * zi) << 1)
             } else {
                 ci - ((zr * zi) << 1)
@@ -392,8 +378,8 @@ fn step(
         }
         FractalKind::Buffalo => {
             // |Re(z^2)| - |Im(z^2)| i: abs both outputs.
-            let re = big_abs(&zr.sqr() - &zi.sqr()) + cr;
-            let im = ci - big_abs((zr * zi) << 1);
+            let re = (&zr.sqr() - &zi.sqr()).abs() + cr;
+            let im = ci - ((zr * zi) << 1).abs();
             (re, im)
         }
         FractalKind::Phoenix => {
@@ -406,7 +392,7 @@ fn step(
         }
         FractalKind::Lambda => {
             // λ·z(1 - z) + c: logistic map plus the usual additive `c`.
-            let re2 = 1 - zr;
+            let re2 = Big::from_f64(1.0, k.precision) - zr;
             let im2 = -zi;
             let lzr = &k.lr * zr - &k.li * zi;
             let lzi = &k.lr * zi + &k.li * zr;
@@ -421,36 +407,20 @@ fn step(
     }
 }
 
-fn big_zero(precision: usize) -> Big {
-    Big::from(0i32).with_precision(precision).value()
-}
-
-/// Absolute value of a `Big`. The sign comes from the `Big` itself: through
-/// f64, anything below ~1e-308 reads as ±0 and would keep its sign.
-fn big_abs(x: Big) -> Big {
-    if x < Big::ZERO { -x } else { x }
-}
-
 /// `(zr + i zi)^power` by repeated complex multiply at `precision` bits.
 fn complex_pow(zr: &Big, zi: &Big, power: u32, precision: usize) -> (Big, Big) {
-    let mut rr = Big::from(1i32).with_precision(precision).value();
-    let mut ri = big_zero(precision);
+    let mut rr = Big::from_f64(1.0, precision);
+    let mut ri = Big::zero(precision);
     for _ in 0..power {
         // (rr + i ri)(zr + i zi) = (rr zr - ri zi) + (rr zi + ri zr) i.
-        let nr = (&rr * zr - &ri * zi).with_precision(precision).value();
-        let ni = (&rr * zi + &ri * zr).with_precision(precision).value();
+        let nr = (&rr * zr - &ri * zi).with_precision(precision);
+        let ni = (&rr * zi + &ri * zr).with_precision(precision);
         rr = nr;
         ri = ni;
     }
     (rr, ri)
 }
 
-/// `true` if `x` is exactly zero (special-cases `ln(0)`). Not via f64,
-/// which flushes values below ~1e-308 to zero.
-fn is_big_zero(x: &Big) -> bool {
-    x.repr().significand().is_zero()
-}
-
 /// `(zr + i zi)^(pr + i pi)` for a complex exponent, via the principal branch
 /// `z^p = exp(p·ln z)` where `ln z = ln|z| + i·arg(z)`. Used by
 /// `ComplexMultibrot`; must be kept in sync with the shader's `cpow`.
@@ -458,14 +428,14 @@ fn is_big_zero(x: &Big) -> bool {
 /// panic; this is the correct limit for the `Re(p) > 0` region the UI
 /// exposes).
 fn complex_pow_complex(zr: &Big, zi: &Big, pr: &Big, pi: &Big, precision: usize) -> (Big, Big) {
-    if is_big_zero(zr) && is_big_zero(zi) {
-        return (big_zero(precision), big_zero(precision));
+    if zr.is_zero() && zi.is_zero() {
+        return (Big::zero(precision), Big::zero(precision));
     }
     let r2 = &zr.sqr() + &zi.sqr();
     let ln_r = r2.ln() >> 1; // 0.5 * ln(r2) = ln(sqrt(r2)); exact halving.
     let theta = zi.atan2(zr);
-    let exp_re = (pr * &ln_r - pi * &theta).with_precision(precision).value();
-    let exp_im = (pr * &theta + pi * &ln_r).with_precision(precision).value();
+    let exp_re = (pr * &ln_r - pi * &theta).with_precision(precision);
+    let exp_im = (pr * &theta + pi * &ln_r).with_precision(precision);
     let mag = exp_re.exp();
     let (sin_a, cos_a) = exp_im.sin_cos();
     (&mag * &cos_a, &mag * &sin_a)
@@ -486,7 +456,7 @@ pub fn compute_set_reference(
     complex_power: (f64, f64),
     morph: Option<(FractalKind, f64)>,
 ) -> RefOrbit {
-    let zero = big_zero(precision);
+    let zero = Big::zero(precision);
     compute_reference(
         &zero,
         &zero,
@@ -511,19 +481,19 @@ mod tests {
     /// `to_f64` reads as ±0.
     #[test]
     fn sign_and_zero_below_f64_range() {
-        let tiny = Big::try_from(1.0_f64).unwrap().with_precision(64).value() >> 5000;
-        assert!(!is_big_zero(&tiny));
-        assert!(is_big_zero(&big_zero(64)));
-        assert_eq!(big_abs(-tiny.clone()), tiny);
-        assert_eq!(big_abs(tiny.clone()), tiny);
+        let tiny = Big::from_f64(1.0, 64) >> 5000;
+        assert!(!tiny.is_zero());
+        assert!(Big::zero(64).is_zero());
+        assert_eq!((-tiny.clone()).abs(), tiny);
+        assert_eq!(tiny.clone().abs(), tiny);
     }
 
     /// The high-precision reference must agree with a plain f64 iteration for a
     /// shallow point (where f64 is accurate).
     #[test]
     fn reference_matches_naive_f64() {
-        let cr = Big::try_from(-0.75_f64).unwrap();
-        let ci = Big::try_from(0.1_f64).unwrap();
+        let cr = Big::from_f64(-0.75, 53);
+        let ci = Big::from_f64(0.1, 53);
         let points = compute_set_reference(
             &cr,
             &ci,
@@ -656,8 +626,8 @@ mod tests {
     /// A point inside the main cardioid never escapes: full-length orbit.
     #[test]
     fn interior_orbit_runs_full_length() {
-        let cr = Big::try_from(-0.2_f64).unwrap();
-        let ci = Big::try_from(0.0_f64).unwrap();
+        let cr = Big::from_f64(-0.2, 53);
+        let ci = Big::from_f64(0.0, 53);
         let points = compute_set_reference(
             &cr,
             &ci,
@@ -676,8 +646,8 @@ mod tests {
     /// Burning Ship reference matches a naive f64 iteration of the same formula.
     #[test]
     fn burning_ship_reference_matches_naive_f64() {
-        let cr = Big::try_from(-1.75_f64).unwrap();
-        let ci = Big::try_from(-0.03_f64).unwrap();
+        let cr = Big::from_f64(-1.75, 53);
+        let ci = Big::from_f64(-0.03, 53);
         let points = compute_set_reference(
             &cr,
             &ci,
@@ -707,8 +677,8 @@ mod tests {
     /// Multibrot (power 3) reference matches a naive f64 cube iteration.
     #[test]
     fn multibrot3_reference_matches_naive_f64() {
-        let cr = Big::try_from(0.3_f64).unwrap();
-        let ci = Big::try_from(0.2_f64).unwrap();
+        let cr = Big::from_f64(0.3, 53);
+        let ci = Big::from_f64(0.2, 53);
         let points = compute_set_reference(
             &cr,
             &ci,
@@ -740,10 +710,10 @@ mod tests {
     /// Julia orbit (fixed c, z0 = center) matches a naive f64 iteration.
     #[test]
     fn julia_reference_matches_naive_f64() {
-        let z0_re = Big::try_from(0.15_f64).unwrap();
-        let z0_im = Big::try_from(-0.1_f64).unwrap();
-        let c_re = Big::try_from(-0.8_f64).unwrap();
-        let c_im = Big::try_from(0.156_f64).unwrap();
+        let z0_re = Big::from_f64(0.15, 53);
+        let z0_im = Big::from_f64(-0.1, 53);
+        let c_re = Big::from_f64(-0.8, 53);
+        let c_im = Big::from_f64(0.156, 53);
         let points = compute_reference(
             &z0_re,
             &z0_im,
@@ -778,10 +748,10 @@ mod tests {
         let (lr, li) = (-0.5_f64, 0.2_f64);
         let (cr, ci) = (0.1_f64, -0.3_f64);
         let points = compute_reference(
-            &Big::try_from(0.2_f64).unwrap(),
-            &Big::try_from(0.1_f64).unwrap(),
-            &Big::try_from(cr).unwrap(),
-            &Big::try_from(ci).unwrap(),
+            &Big::from_f64(0.2, 53),
+            &Big::from_f64(0.1, 53),
+            &Big::from_f64(cr, 53),
+            &Big::from_f64(ci, 53),
             60,
             200,
             FractalKind::Lambda,
@@ -807,8 +777,8 @@ mod tests {
     /// Celtic reference matches a naive f64 iteration: real = |x^2 - y^2| + cr.
     #[test]
     fn celtic_reference_matches_naive_f64() {
-        let cr = Big::try_from(-0.6_f64).unwrap();
-        let ci = Big::try_from(0.4_f64).unwrap();
+        let cr = Big::from_f64(-0.6, 53);
+        let ci = Big::from_f64(0.4, 53);
         let points = compute_set_reference(
             &cr,
             &ci,
@@ -839,8 +809,8 @@ mod tests {
     /// real = x^2 - y^2 + cr, imag = -2·x·|y| + ci.
     #[test]
     fn perpendicular_reference_matches_naive_f64() {
-        let cr = Big::try_from(-0.7_f64).unwrap();
-        let ci = Big::try_from(-0.2_f64).unwrap();
+        let cr = Big::from_f64(-0.7, 53);
+        let ci = Big::from_f64(-0.2, 53);
         let points = compute_set_reference(
             &cr,
             &ci,
@@ -871,8 +841,8 @@ mod tests {
     /// real = |x^2 - y^2| + cr, imag = -|2·x·y| + ci.
     #[test]
     fn buffalo_reference_matches_naive_f64() {
-        let cr = Big::try_from(-1.2_f64).unwrap();
-        let ci = Big::try_from(-0.35_f64).unwrap();
+        let cr = Big::from_f64(-1.2, 53);
+        let ci = Big::from_f64(-0.35, 53);
         let points = compute_set_reference(
             &cr,
             &ci,
@@ -903,8 +873,8 @@ mod tests {
     /// `z_{n+1} = z_n^2 + c + p·z_{n-1}` (z_0 = 0, z_{-1} = 0).
     #[test]
     fn phoenix_reference_matches_naive_f64() {
-        let cr = Big::try_from(0.5667_f64).unwrap();
-        let ci = Big::try_from(0.0_f64).unwrap();
+        let cr = Big::from_f64(0.5667, 53);
+        let ci = Big::from_f64(0.0, 53);
         let p = (-0.5_f64, 0.0_f64);
         let points = compute_set_reference(
             &cr,
@@ -942,8 +912,8 @@ mod tests {
     /// iteration of `z^p = exp(p·ln z)`.
     #[test]
     fn complex_multibrot_reference_matches_naive_f64() {
-        let cr = Big::try_from(0.1_f64).unwrap();
-        let ci = Big::try_from(-0.2_f64).unwrap();
+        let cr = Big::from_f64(0.1, 53);
+        let ci = Big::from_f64(-0.2, 53);
         let power = (2.5_f64, 0.3_f64);
         let points = compute_set_reference(
             &cr,
@@ -987,8 +957,8 @@ mod tests {
 
     fn set_ref(cr: f64, ci: f64, kind: FractalKind, morph: Option<(FractalKind, f64)>) -> RefOrbit {
         compute_set_reference(
-            &Big::try_from(cr).unwrap(),
-            &Big::try_from(ci).unwrap(),
+            &Big::from_f64(cr, 53),
+            &Big::from_f64(ci, 53),
             60,
             200,
             kind,
diff --git a/src/main.rs b/src/main.rs
index e461e8c..24947e1 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -11,6 +11,7 @@
 // and calls the wasm `main`, which boots eframe onto the page's <canvas>.
 
 mod app;
+mod bignum;
 mod camera;
 mod fractal;
 mod lights;
diff --git a/src/view.rs b/src/view.rs
index 6daae08..e5f0df6 100644
--- a/src/view.rs
+++ b/src/view.rs
@@ -1,6 +1,6 @@
 //! Camera / view state over the complex plane.
 //!
-//! The center is stored in arbitrary precision (`FBig`) — this is what lets us
+//! The center is stored in arbitrary precision ([`Big`]) — this is what lets us
 //! zoom far past f64's ~1e13x limit. The pixel *scale* is a [`Scale`]: an
 //! f64 mantissa with its own `i32` binary exponent, so it isn't bound by
 //! f64's ~1e-308 range either (the floor, `Scale::MIN`, only keeps the GPU's
@@ -10,11 +10,7 @@
 
 use core::str::FromStr;
 
-use dashu_float::round::mode::HalfAway;
-use dashu_float::{DBig, FBig};
-
-/// Arbitrary-precision binary float (base 2, round-half-away). One coordinate.
-pub type Big = FBig<HalfAway, 2>;
+pub use crate::bignum::Big;
 
 /// Half-height (complex units) of the default view; also the zoom-1 reference.
 pub const DEFAULT_HALF_HEIGHT: f64 = 1.25;
@@ -194,28 +190,37 @@ impl core::fmt::Display for Scale {
             };
         }
         // Out of f64's range: round the exact decimal expansion instead.
-        let sig = f.precision().map_or(17, |p| p + 1);
-        let dec = self
-            .to_big()
-            .to_decimal()
-            .value()
-            .with_precision(sig)
-            .value();
-        let repr = dec.repr();
-        let digits = repr.significand().to_string();
-        let digits = digits.trim_end_matches('0');
-        let digits = if digits.is_empty() { "0" } else { digits };
-        // value = significand · 10^exponent; move the point after the first digit.
-        let exp10 = repr.exponent() + repr.significand().to_string().len() as isize - 1;
-        let (head, tail) = digits.split_at(1);
-        let tail = match f.precision() {
-            Some(p) => format!("{tail:0<p$}"),
-            None => tail.to_string(),
+        let big = self.to_big();
+        let sci = |sig: usize, pad: Option<usize>| {
+            let parts = big.to_decimal_parts(sig);
+            let digits = if parts.digits.is_empty() {
+                "0"
+            } else {
+                &parts.digits
+            };
+            // value = 0.digits · 10^exp10; move the point after the first digit.
+            let exp10 = parts.exp10 - 1;
+            let (head, tail) = digits.split_at(1);
+            let tail = match pad {
+                Some(p) => format!("{tail:0<p$}"),
+                None => tail.to_string(),
+            };
+            if tail.is_empty() {
+                format!("{head}e{exp10}")
+            } else {
+                format!("{head}.{tail}e{exp10}")
+            }
         };
-        if tail.is_empty() {
-            write!(f, "{head}e{exp10}")
-        } else {
-            write!(f, "{head}.{tail}e{exp10}")
+        match f.precision() {
+            Some(p) => f.write_str(&sci(p + 1, Some(p))),
+            None => {
+                // Like `{:e}` on f64: the shortest string that parses back.
+                let s = (1..17)
+                    .map(|sig| sci(sig, None))
+                    .find(|s| s.parse::<Scale>() == Ok(*self))
+                    .unwrap_or_else(|| sci(17, None));
+                f.write_str(&s)
+            }
         }
     }
 }
@@ -237,18 +242,12 @@ impl FromStr for Scale {
             };
         }
         // Too small (or large) for f64: go through an exact decimal.
-        let dec = DBig::from_str(s).map_err(|_| ())?;
-        let bin: Big = dec.with_base_and_precision::<2>(64).value();
-        if bin < Big::ZERO {
+        let bin = Big::from_decimal_str(s, 64).ok_or(())?;
+        if bin.is_negative() {
             return Err(());
         }
-        let repr = bin.repr();
-        let digits = repr.digits();
-        if digits == 0 {
-            return Err(());
-        }
-        let top = repr.exponent() + digits as isize - 1;
-        let m = (bin.clone() >> top).to_f64().value();
+        let top = bin.log2_floor().ok_or(())?;
+        let m = (bin >> top).to_f64();
         let e = top.clamp(i32::MIN as isize, i32::MAX as isize) as i32;
         Ok(Self::from_parts(m, e))
     }
@@ -312,10 +311,10 @@ impl ViewState {
     pub fn sync_precision(&mut self) {
         let bits = self.precision_bits();
         if self.center_re.precision() < bits {
-            self.center_re = self.center_re.clone().with_precision(bits).value();
+            self.center_re = self.center_re.clone().with_precision(bits);
         }
         if self.center_im.precision() < bits {
-            self.center_im = self.center_im.clone().with_precision(bits).value();
+            self.center_im = self.center_im.clone().with_precision(bits);
         }
     }
 
@@ -360,8 +359,7 @@ impl ViewState {
 /// Parse a decimal string (any number of digits) losslessly into a `Big` with at
 /// least `bits` of precision. Used for share links and debug view specs.
 pub fn big_from_decimal_str(s: &str, bits: usize) -> Option<Big> {
-    let dec = DBig::from_str(s.trim()).ok()?;
-    Some(dec.with_base_and_precision::<2>(bits.max(53)).value())
+    Big::from_decimal_str(s, bits)
 }
 
 /// Parse a "re,im,half_height[,iterations]" spec (re/im decimal, parsed at
@@ -440,10 +438,10 @@ pub fn interpolate_view(from: &ViewState, to: &ViewState, t: f64) -> ViewState {
         // Zooming out: g = (1 - q^(t-1)) / (1 - q^-1), every term bounded.
         big_from_f64(((t - 1.0) * d * ln2).exp_m1() / (-d * ln2).exp_m1(), bits)
     };
-    let re0 = from.center_re.clone().with_precision(bits).value();
-    let im0 = from.center_im.clone().with_precision(bits).value();
-    let re1 = to.center_re.clone().with_precision(bits).value();
-    let im1 = to.center_im.clone().with_precision(bits).value();
+    let re0 = from.center_re.clone().with_precision(bits);
+    let im0 = from.center_im.clone().with_precision(bits);
+    let re1 = to.center_re.clone().with_precision(bits);
+    let im1 = to.center_im.clone().with_precision(bits);
     let center_re = &re1 + &(&(&re0 - &re1) * &g_big);
     let center_im = &im1 + &(&(&im0 - &im1) * &g_big);
     ViewState::with_center(center_re, center_im, half_height)
@@ -456,12 +454,7 @@ pub fn interpolate_f64(from: f64, to: f64, t: f64) -> f64 {
 
 /// Render a `Big` as a decimal string with `sig_digits` significant digits.
 pub fn big_to_decimal_str(x: &Big, sig_digits: usize) -> String {
-    let dec = x
-        .to_decimal()
-        .value()
-        .with_precision(sig_digits.max(1))
-        .value();
-    format!("{dec}")
+    x.to_decimal_string(sig_digits)
 }
 
 /// Precision (bits) needed to resolve the center at a given half-height.
@@ -472,12 +465,9 @@ pub fn precision_for(half_height: Scale) -> usize {
     (zoom_bits + GUARD_BITS).clamp(53, MAX_PRECISION_BITS)
 }
 
-/// Build an `FBig` from an f64 with an explicit precision context.
+/// Build a `Big` from an f64 with an explicit precision.
 pub fn big_from_f64(x: f64, bits: usize) -> Big {
-    Big::try_from(x)
-        .unwrap_or_default()
-        .with_precision(bits)
-        .value()
+    Big::from_f64(x, bits)
 }
 
 #[cfg(test)]
@@ -489,8 +479,8 @@ mod tests {
     }
 
     fn re_im_f64(v: &ViewState) -> (f64, f64) {
-        let re: f64 = v.center_re.to_decimal().value().to_f64().value();
-        let im: f64 = v.center_im.to_decimal().value().to_f64().value();
+        let re: f64 = v.center_re.to_f64();
+        let im: f64 = v.center_im.to_f64();
         (re, im)
     }
 
@@ -612,8 +602,8 @@ mod tests {
             prev = mid.half_height;
             // Offset from the target, in units of the view's half-height.
             let k = -mid.half_height.exponent() as isize;
-            let dre = ((&mid.center_re - &to.center_re) << k).to_f64().value();
-            let dim = ((&mid.center_im - &to.center_im) << k).to_f64().value();
+            let dre = ((&mid.center_re - &to.center_re) << k).to_f64();
+            let dim = ((&mid.center_im - &to.center_im) << k).to_f64();
             let ratio = (dre * dre + dim * dim).sqrt() / mid.half_height.scaled_f64(k as i32);
             assert!(ratio > 0.01 && ratio < 10.0, "t={t}: ratio {ratio}");
         }
diff --git a/src/worker.rs b/src/worker.rs
index d6cb4f5..c403f72 100644
--- a/src/worker.rs
+++ b/src/worker.rs
@@ -1,7 +1,7 @@
 //! Native background worker for reference-orbit computation.
 //!
 //! At deep zoom the high-precision reference can take many milliseconds (tens of
-//! thousands of `FBig` iterations), which would stutter the UI if done inline.
+//! thousands of `Big` iterations), which would stutter the UI if done inline.
 //! This runs it on a thread and coalesces bursts of requests (e.g. during a
 //! drag) down to the most recent one. On the web we compute inline instead
 //! (browsers need a Web Worker for threads); see `app.rs`.