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Audio: fix audio buffer SIMD alignment issues

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Signed-off-by: Stephen Gutekanst <stephen@hexops.com>
This commit is contained in:
Stephen Gutekanst 2024-12-29 13:47:51 -07:00
parent d848d2e26e
commit 1a7753936b
1 changed files with 34 additions and 45 deletions
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79
src/Audio.zig
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@ -11,6 +11,14 @@ pub const mach_module = .mach_audio;
pub const mach_systems = .{ .init, .tick, .deinit };
/// The length of a @Vector(len, f32) used for SIMD mixing of audio buffers. Audio buffers must be
/// aligned to simd_vector_length * @sizeOf(f32).
pub const simd_vector_length = std.simd.suggestVectorLength(f32) orelse 1;
/// The number of f32s which should be reserved for padding at the start of an []f32 buffer, assuming
/// it is @alignOf(f32) / 4-byte aligned, in order to achieve @Vector(simd_vector_length, f32) alignment.
pub const simd_vector_f32_buffer_padding = (simd_vector_length - (4 % simd_vector_length)) % simd_vector_length;
const log = std.log.scoped(mach_module);
// The number of milliseconds worth of audio to render ahead of time. The lower this number is, the
@ -25,7 +33,7 @@ buffers: mach.Objects(
.{},
struct {
/// The actual audio samples
samples: []const f32,
samples: []const f32 align(simd_vector_length),
/// The number of channels in the samples buffer
channels: u8,
@ -138,11 +146,11 @@ pub fn tick(audio: *Audio, audio_mod: mach.Mod(Audio)) !void {
// Ensure our f32 mixing buffer has enough space for the samples we will render right now.
// This will allocate to grow but never shrink.
var mixing_buffer = if (audio.mixing_buffer) |*b| b else blk: {
const b = try std.ArrayListUnmanaged(f32).initCapacity(allocator, render_num_samples);
const b = try std.ArrayListUnmanaged(f32).initCapacity(allocator, simd_vector_f32_buffer_padding + render_num_samples);
audio.mixing_buffer = b;
break :blk &audio.mixing_buffer.?;
};
try mixing_buffer.resize(allocator, render_num_samples); // grows, but never shrinks
try mixing_buffer.resize(allocator, simd_vector_f32_buffer_padding + render_num_samples); // grows, but never shrinks
// Zero the mixing buffer to silence: if no audio is mixed in below, then we want silence
// not undefined memory noise.
@ -160,16 +168,17 @@ pub fn tick(audio: *Audio, audio_mod: mach.Mod(Audio)) !void {
defer audio.buffers.setValue(buf_id, buffer);
const channels_diff = player_channels - buffer.channels + 1;
const to_read = (@min(buffer.samples.len - buffer.index, mixing_buffer.items.len) / channels_diff) + @rem(@min(buffer.samples.len - buffer.index, mixing_buffer.items.len), channels_diff);
const mixing_buffer_len = mixing_buffer.items.len - simd_vector_f32_buffer_padding;
const to_read = (@min(buffer.samples.len - buffer.index, mixing_buffer_len - simd_vector_f32_buffer_padding) / channels_diff) + @rem(@min(buffer.samples.len - buffer.index, mixing_buffer_len), channels_diff);
if (buffer.channels == 1 and player_channels > 1) {
// Duplicate samples for mono sounds
var i: usize = 0;
var i: usize = simd_vector_f32_buffer_padding;
for (buffer.samples[buffer.index..][0..to_read]) |sample| {
mixSamplesDuplicate(mixing_buffer.items[i..][0..player_channels], sample * buffer.volume);
i += player_channels;
}
} else {
mixSamples(mixing_buffer.items[0..to_read], buffer.samples[buffer.index..][0..to_read], buffer.volume);
mixSamples(mixing_buffer.items[simd_vector_f32_buffer_padding..to_read], buffer.samples[buffer.index..][0..to_read], buffer.volume);
}
if (buffer.index + to_read >= buffer.samples.len) {
@ -186,10 +195,10 @@ pub fn tick(audio: *Audio, audio_mod: mach.Mod(Audio)) !void {
// samples to the format the driver expects.
const out_buffer_len = render_num_samples * player.format().size();
const out_buffer = try audio.output.writableWithSize(out_buffer_len); // TODO(audio): handle potential OOM here better
std.debug.assert(mixing_buffer.items.len == render_num_samples);
std.debug.assert((mixing_buffer.items.len - simd_vector_f32_buffer_padding) == render_num_samples);
sysaudio.convertTo(
f32,
mixing_buffer.items,
mixing_buffer.items[simd_vector_f32_buffer_padding..],
player.format(),
out_buffer[0..out_buffer_len], // writableWithSize may return a larger slice than needed
);
@ -255,48 +264,28 @@ fn writeFn(audio_opaque: ?*anyopaque, output: []u8) void {
}
}
// TODO(audio): remove this switch, currently ReleaseFast/ReleaseSmall have some weird behavior if
// we use suggestVectorLength
const vector_length = switch (builtin.mode) {
.Debug, .ReleaseSafe => std.simd.suggestVectorLength(f32),
else => null,
};
inline fn mixSamples(a: []f32, b: []const f32, volume: f32) void {
inline fn mixSamples(
a: []align(simd_vector_length) f32,
b: []align(simd_vector_length) const f32,
volume: f32,
) void {
std.debug.assert(a.len >= b.len);
const Vec = @Vector(simd_vector_length, f32);
const vec_blocks_len = b.len - (b.len % simd_vector_length);
var i: usize = 0;
// use SIMD when available
if (vector_length) |vec_len| {
const Vec = @Vector(vec_len, f32);
const vec_blocks_len = b.len - (b.len % vec_len);
while (i < vec_blocks_len) : (i += vec_len) {
const b_vec: Vec = b[i..][0..vec_len].*;
const a_vec: *Vec = @ptrCast(@alignCast(a[i..][0..vec_len]));
a_vec.* += b_vec * @as(Vec, @splat(volume));
}
}
for (a[i..b.len], b[i..]) |*a_sample, b_sample| {
a_sample.* += b_sample * volume;
while (i < vec_blocks_len) : (i += simd_vector_length) {
const b_vec: Vec = b[i..][0..simd_vector_length].*;
const a_vec: *Vec = @ptrCast(@alignCast(a[i..][0..simd_vector_length]));
a_vec.* += b_vec * @as(Vec, @splat(volume));
}
}
inline fn mixSamplesDuplicate(a: []f32, b: f32) void {
inline fn mixSamplesDuplicate(a: []align(simd_vector_length) f32, b: f32) void {
const Vec = @Vector(simd_vector_length, f32);
const vec_blocks_len = a.len - (a.len % simd_vector_length);
var i: usize = 0;
// use SIMD when available
if (vector_length) |vec_len| {
const Vec = @Vector(vec_len, f32);
const vec_blocks_len = a.len - (a.len % vec_len);
while (i < vec_blocks_len) : (i += vec_len) {
const a_vec: *Vec = @ptrCast(@alignCast(a[i..][0..vec_len]));
a_vec.* += @as(Vec, @splat(b));
}
}
for (a[i..]) |*a_sample| {
a_sample.* += b;
while (i < vec_blocks_len) : (i += simd_vector_length) {
const a_vec: *Vec = @ptrCast(@alignCast(a[i..][0..simd_vector_length]));
a_vec.* += @as(Vec, @splat(b));
}
}