Port wasm solver to C and add regression coverage

docs/guide/widget.md

@@ -4,7 +4,7 @@ outline: [2, 3, 4]
 
 # Widget
 
-Cap's client-side widget handles requesting, solving and displaying challenges using a native web component and rust-flavoured WASM. It also includes the [programmatic mode](./programmatic).
+Cap's client-side widget handles requesting, solving and displaying challenges using a native web component and a C-based WASM solver. It also includes the [programmatic mode](./programmatic).
 
 ## Installation
 

docs/guide/workings.md

@@ -15,7 +15,7 @@ By the way, this is a more technical explanation of how Cap works. If you're loo
 
 #### Computing the solution
 
-5. The widget uses Rust-flavoured WASM and Web Workers to solve the challenges in parallel:
+5. The widget uses a C-based WASM solver and Web Workers to solve the challenges in parallel:
    - Each worker attempts to find a valid nonce by repeatedly:
      - Combining the salt with different nonce values
      - Computing the SHA-256 hash of this combination

wasm/benchmark/README.md

@@ -0,0 +1,42 @@
+# Benchmark
+
+This benchmark compares the historical Rust solver from commit `da725dba93f61099d264bc597d22ff388d09d2ad` against the current C solver at `HEAD`.
+
+## What it does
+
+- Rebuilds the Rust implementation from `benchmark/rust`
+- Rebuilds the current C implementation from `src/c`
+- Loads both Node targets
+- Verifies the same challenge cases before timing them
+- Reports average time per solve and the relative speedup
+
+## Run it
+
+```bash
+bun --cwd benchmark run bench
+```
+
+Optional environment variables:
+
+- `BENCH_ITERATIONS` controls the timed loops, default `10`
+- `BENCH_WARMUP` controls warmup rounds, default `2`
+
+## Browser version
+
+This repo also includes a browser-hosted version that loads the wasm modules in a real browser
+context.
+
+```bash
+bun --cwd benchmark run bench:browser
+```
+
+Then open the printed local URL. You can override the browser benchmark loop counts with query
+parameters like `?iterations=20&warmup=3`.
+
+## Requirements
+
+- `make`
+- `clang`
+- `git`
+- `rustup`
+- the `wasm32-unknown-unknown` target installed for the rustup-managed toolchain

wasm/benchmark/bench.js

@@ -0,0 +1,62 @@
+import path from "node:path";
+import { createRequire } from "node:module";
+import { buildAll, headDir, rustDir } from "./build-artifacts.js";
+import { benchmarkSolver, rustBaselineCommit, verifySolver } from "./shared.js";
+
+const iterations = Number.parseInt(process.env.BENCH_ITERATIONS ?? "10", 10);
+const warmupRounds = Number.parseInt(process.env.BENCH_WARMUP ?? "2", 10);
+
+if (!Number.isFinite(iterations) || iterations < 1) {
+  throw new Error("BENCH_ITERATIONS must be a positive integer");
+}
+
+if (!Number.isFinite(warmupRounds) || warmupRounds < 0) {
+  throw new Error("BENCH_WARMUP must be a non-negative integer");
+}
+
+function loadSolvePow(modulePath) {
+  const require = createRequire(import.meta.url);
+  const mod = require(modulePath);
+
+  if (typeof mod.solve_pow !== "function") {
+    throw new Error(`missing solve_pow in ${modulePath}`);
+  }
+
+  return mod.solve_pow;
+}
+
+buildAll();
+
+const headSolvePow = loadSolvePow(path.join(headDir, "cap_wasm.js"));
+const rustSolvePow = loadSolvePow(path.join(rustDir, "cap_wasm.js"));
+
+verifySolver("HEAD (C)", headSolvePow);
+verifySolver(`Rust (${rustBaselineCommit.slice(0, 7)})`, rustSolvePow);
+
+const headResult = benchmarkSolver("HEAD (C)", headSolvePow, {
+  iterations,
+  warmupRounds,
+});
+const rustResult = benchmarkSolver(`Rust (${rustBaselineCommit.slice(0, 7)})`, rustSolvePow, {
+  iterations,
+  warmupRounds,
+});
+
+if (headResult.checksum !== rustResult.checksum) {
+  throw new Error(
+    `checksum mismatch: ${headResult.checksum.toString()} != ${rustResult.checksum.toString()}`,
+  );
+}
+
+console.log(`\nBenchmark results`);
+console.log(
+  `${headResult.label.padEnd(14)} ${headResult.elapsedMs.toFixed(2)} ms total ` +
+    `(${headResult.perSolveMs.toFixed(4)} ms/solve)`,
+);
+console.log(
+  `${rustResult.label.padEnd(14)} ${rustResult.elapsedMs.toFixed(2)} ms total ` +
+    `(${rustResult.perSolveMs.toFixed(4)} ms/solve)`,
+);
+console.log(
+  `Speedup: ${(rustResult.perSolveMs / headResult.perSolveMs).toFixed(2)}x faster on HEAD`,
+);

wasm/benchmark/browser/bench.js

@@ -0,0 +1,103 @@
+import { benchmarkSolver, challengeCases, rustBaselineCommit, verifySolver } from "../shared.js";
+
+const statusEl = document.getElementById("status");
+const metaEl = document.getElementById("meta");
+const outputEl = document.getElementById("output");
+
+function log(line) {
+  outputEl.textContent += `${line}\n`;
+  console.log(line);
+}
+
+function fail(error) {
+  const message = error instanceof Error ? error.stack ?? error.message : String(error);
+  statusEl.textContent = "Failed.";
+  outputEl.textContent += `${message}\n`;
+  console.error(error);
+}
+
+window.addEventListener("error", (event) => {
+  fail(event.error ?? event.message);
+});
+
+window.addEventListener("unhandledrejection", (event) => {
+  fail(event.reason);
+});
+
+function readIntParam(name, fallback) {
+  const value = new URLSearchParams(location.search).get(name);
+
+  if (value === null) {
+    return fallback;
+  }
+
+  const parsed = Number.parseInt(value, 10);
+  if (!Number.isFinite(parsed) || parsed < 0) {
+    throw new Error(`${name} must be a non-negative integer`);
+  }
+
+  return parsed;
+}
+
+const iterations = readIntParam("iterations", 10);
+const warmupRounds = readIntParam("warmup", 2);
+
+metaEl.textContent = `iterations=${iterations}, warmup=${warmupRounds}, cases=${challengeCases.length}`;
+
+try {
+  const cacheToken = Date.now();
+  const headModule = await import(`/out/head/browser/cap_wasm.js?cache=${cacheToken}`);
+  const rustModule = await import(`/out/rust/browser/cap_wasm.js?cache=${cacheToken}`);
+
+  const initHead = headModule.default;
+  const headSolvePow = headModule.solve_pow;
+  const initRust = rustModule.default;
+  const rustSolvePow = rustModule.solve_pow;
+
+  statusEl.textContent = "Loading wasm modules...";
+  log("Loading wasm modules...");
+  await Promise.all([initHead(), initRust()]);
+  log("Wasm modules loaded.");
+
+  statusEl.textContent = "Verifying solver outputs...";
+  log("Verifying solver outputs...");
+  await new Promise((resolve) => requestAnimationFrame(resolve));
+
+  verifySolver("HEAD (C)", headSolvePow);
+  verifySolver(`Rust (${rustBaselineCommit.slice(0, 7)})`, rustSolvePow);
+  log("Verification complete.");
+
+  statusEl.textContent = "Running benchmark...";
+  log("Running benchmark...");
+  await new Promise((resolve) => requestAnimationFrame(resolve));
+
+  const headResult = benchmarkSolver("HEAD (C)", headSolvePow, {
+    iterations,
+    warmupRounds,
+  });
+  const rustResult = benchmarkSolver(`Rust (${rustBaselineCommit.slice(0, 7)})`, rustSolvePow, {
+    iterations,
+    warmupRounds,
+  });
+
+  if (headResult.checksum !== rustResult.checksum) {
+    throw new Error(
+      `checksum mismatch: ${headResult.checksum.toString()} != ${rustResult.checksum.toString()}`,
+    );
+  }
+
+  log("Benchmark results");
+  log(
+    `${headResult.label.padEnd(14)} ${headResult.elapsedMs.toFixed(2)} ms total ` +
+      `(${headResult.perSolveMs.toFixed(4)} ms/solve)`,
+  );
+  log(
+    `${rustResult.label.padEnd(14)} ${rustResult.elapsedMs.toFixed(2)} ms total ` +
+      `(${rustResult.perSolveMs.toFixed(4)} ms/solve)`,
+  );
+  log(`Speedup: ${(rustResult.perSolveMs / headResult.perSolveMs).toFixed(2)}x faster on HEAD`);
+
+  statusEl.textContent = "Done.";
+} catch (error) {
+  fail(error);
+}

wasm/benchmark/browser/index.html

@@ -0,0 +1,109 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1" />
+    <title>Wasm Browser Benchmark</title>
+    <link rel="icon" href="data:," />
+    <style>
+      :root {
+        color-scheme: dark;
+        --bg: #0b1020;
+        --panel: rgba(13, 21, 42, 0.88);
+        --panel-border: rgba(255, 255, 255, 0.12);
+        --text: #e8edf7;
+        --muted: #94a3b8;
+        --accent: #7dd3fc;
+        --accent-2: #a78bfa;
+      }
+
+      html,
+      body {
+        margin: 0;
+        min-height: 100%;
+        background:
+          radial-gradient(circle at top left, rgba(125, 211, 252, 0.16), transparent 28%),
+          radial-gradient(circle at top right, rgba(167, 139, 250, 0.2), transparent 26%),
+          linear-gradient(180deg, #070b15 0%, var(--bg) 100%);
+        color: var(--text);
+        font: 16px/1.5 Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI",
+          sans-serif;
+      }
+
+      body {
+        display: grid;
+        place-items: center;
+        padding: 24px;
+        box-sizing: border-box;
+      }
+
+      main {
+        width: min(900px, 100%);
+        border: 1px solid var(--panel-border);
+        background: var(--panel);
+        backdrop-filter: blur(18px);
+        border-radius: 20px;
+        padding: 28px;
+        box-shadow: 0 24px 80px rgba(0, 0, 0, 0.35);
+      }
+
+      h1 {
+        margin: 0 0 8px;
+        font-size: clamp(1.8rem, 4vw, 3rem);
+        line-height: 1.05;
+      }
+
+      p {
+        margin: 0;
+        color: var(--muted);
+      }
+
+      pre {
+        margin: 24px 0 0;
+        padding: 18px;
+        overflow: auto;
+        border-radius: 16px;
+        background: rgba(2, 6, 23, 0.6);
+        border: 1px solid rgba(148, 163, 184, 0.18);
+        color: var(--text);
+        white-space: pre-wrap;
+      }
+
+      .status {
+        margin-top: 20px;
+        color: var(--accent);
+        font-weight: 600;
+        letter-spacing: 0.01em;
+      }
+
+      .meta {
+        margin-top: 8px;
+        color: var(--muted);
+        font-size: 0.95rem;
+      }
+    </style>
+  </head>
+  <body>
+    <main>
+      <h1>Wasm Browser Benchmark</h1>
+      <p>
+        Runs the C and Rust solvers in an actual browser context and compares their average solve
+        time.
+      </p>
+      <div class="status" id="status">Waiting to load wasm modules...</div>
+      <div class="meta" id="meta"></div>
+      <pre id="output"></pre>
+    </main>
+    <script type="module">
+      const status = document.getElementById("status");
+      status.textContent = "Booting benchmark...";
+
+      import(`/browser/bench.js?cache=${Date.now()}`).catch((error) => {
+        status.textContent = "Failed to boot.";
+        console.error(error);
+        const output = document.getElementById("output");
+        output.textContent = `${error?.stack ?? error?.message ?? String(error)}\n`;
+      });
+    </script>
+  </body>
+</html>