Initial commit

test_audio_wasm/.gitignore

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+*.o
+*.wasm

test_audio_wasm/Makefile

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+CFLAGS = -Wall -Wextra -pedantic -std=c23 \
+	-Wconversion -Wdouble-promotion \
+	-Wno-unused-parameter -Wno-unused-function -Wno-sign-conversion \
+	-fsanitize=undefined \
+	--target=wasm32 -O1 -flto -ffreestanding -fno-builtin -nostdlib
+
+math.o: math.c
+	clang $(CFLAGS) -c math.c -o math.o
+
+beep.wasm: beep.c math.o
+	clang $(CFLAGS) \
+		-Wl,--no-entry \
+		-Wl,--export=beep \
+		-Wl,--export=get_samples \
+		beep.c math.o \
+		-o beep.wasm

test_audio_wasm/beep.c

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+#include <stdint.h>
+#include "math.h"
+#define SAMPLE_COUNT 44100
+
+static float SAMPLES[SAMPLE_COUNT];
+
+float* get_samples() { return SAMPLES; }
+
+void beep(uint32_t sample_rate, float freq) {
+    for (int i = 0; i < SAMPLE_COUNT; ++i) {
+        SAMPLES[i] = sintau((float)i * freq / (float)sample_rate);
+    }
+}

test_audio_wasm/index.html

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+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>Test</title>
+    <style>
+        body {
+            margin: 0;
+            padding: 0;
+            overflow: hidden;
+            background-color: #000000;
+            display: flex;
+            justify-content: center;
+            align-items: center;
+            height: 100vh;
+        }
+    </style>
+</head>
+<body>
+</body>
+<script src="index.js" type="module"></script>
+</html>

test_audio_wasm/index.js

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+const { instance } = await WebAssembly.instantiateStreaming(fetch("beep.wasm"));
+
+let ctx = undefined;
+
+const count = 44100;
+const ptr = instance.exports.get_samples();
+
+async function playTone(frequency = 440) {
+  ctx ??= new AudioContext();
+  await ctx.resume();
+
+  instance.exports.beep(ctx.sampleRate, frequency);
+  const audioBuffer = ctx.createBuffer(1, count, ctx.sampleRate);
+  const audioChannel = audioBuffer.getChannelData(0);
+  audioChannel.set(new Float32Array(instance.exports.memory.buffer, ptr, count));
+
+  const src = ctx.createBufferSource();
+  src.buffer = audioBuffer;
+  src.connect(ctx.destination);
+  src.start();
+}
+
+window.addEventListener("click", () => playTone(440));

test_audio_wasm/math.c

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+#include "math.h"
+
+__attribute__((always_inline))
+static float fminf(float a, float b) {
+    return a < b ? a : b;
+}
+
+/* Approach 1: polynomial; input in radians. */
+static float sin_poly_radians(float x)
+{
+    x *= 0.159155f;          /* approximately 1 / (2*pi) */
+    x -= __builtin_floorf(x);          /* reduce to [0, 1) */
+    float xx = x * x;
+    float y = -6.87897f;
+    y = y * xx + 33.7755f;
+    y = y * xx - 72.5257f;
+    y = y * xx + 80.5874f;
+    y = y * xx - 41.2408f;
+    y = y * xx + 6.28077f;
+    return x * y;
+}
+
+// Approach 2: rational approximation; input in turns (1.0 = 2*pi radians)
+// Calculate sin(tau x) (where x is in the range [0, 1]) using Bhaskara I's approximation
+// https://en.wikipedia.org/wiki/Bhaskara_I%27s_sine_approximation_formula
+// Accurate to about 0.2%
+static float sin_rational_tau(float x)
+{
+    float frac = x - __builtin_floorf(x);
+    float sign = 0.5f - frac;
+    float y = 2.0f * fminf(frac, 1.0f - frac);
+    float q = y * (1.0f - y);
+    float approximation = (16.0f * q) / (5.0f - 4.0f * q);
+    return __builtin_copysignf(approximation, sign);
+}
+
+/* Approach 3: folded polynomial; input in turns (1.0 = 2*pi radians). */
+static float sin_folded_poly_tau(float x)
+{
+    union { uint32_t i; float f; } coeffs[6] = {
+        { 0x4261c73fu }, { 0x4113e0d9u }, { 0xc22aaa4bu },
+        { 0x3da6b273u }, { 0x40c90140u }, { 0x36d0957eu }
+    };
+
+    float frac = x - __builtin_floorf(x);
+    float x1 = __builtin_fabsf(frac - 0.5f);
+    float t = fminf(0.5f - x1, x1); /* fold to [0, 0.25] */
+
+    float y = 0.0f;
+    for (int i = 0; i < 6; ++i) {
+        y = y * t + coeffs[i].f;
+    }
+
+    return __builtin_copysignf(y, 0.5f - frac);
+}
+
+float sintau(float x) {
+    return sin_rational_tau(x);
+}

test_audio_wasm/math.h

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+#ifndef _MATH_H
+#define _MATH_H
+#include <stdint.h>
+
+#define PI 3.14159265358979323846
+
+float sintau(float x);
+
+#endif