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Merge a4b70f3c49 into e4be00f949

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Giuseppe Cesarano 2025-11-25 13:29:47 +01:00 • committed by GitHub
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1 changed files with 32 additions and 29 deletions
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61
lib/std/mem.zig
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@ -1280,7 +1280,6 @@ pub const indexOfScalarPos = findScalarPos;
/// Returns null if the value is not found.
pub fn findScalarPos(comptime T: type, slice: []const T, start_index: usize, value: T) ?usize {
if (start_index >= slice.len) return null;
var i: usize = start_index;
if (use_vectors_for_comparison and
!std.debug.inValgrind() and // https://github.com/ziglang/zig/issues/17717
@ -1296,39 +1295,43 @@ pub fn findScalarPos(comptime T: type, slice: []const T, start_index: usize, val
//
// This may differ for other arch's. Arm for example costs a cycle when loading across a cache
// line so explicit alignment prologues may be worth exploration.
// Unrolling here is ~10% improvement. We can then do one bounds check every 2 blocks
// instead of one which adds up.
const Block = @Vector(block_len, T);
if (i + 2 * block_len < slice.len) {
const mask: Block = @splat(value);
while (true) {
inline for (0..2) |_| {
const block: Block = slice[i..][0..block_len].*;
const matches = block == mask;
if (@reduce(.Or, matches)) {
return i + std.simd.firstTrue(matches).?;
}
i += block_len;
}
if (i + 2 * block_len >= slice.len) break;
const mask: Block = @splat(value);
while (i <= slice.len -| block_len * 4 and slice.len >= block_len * 4) : (i += block_len * 4) {
var matches: [4]@TypeOf(mask == mask) = undefined;
inline for (0..4) |j| {
const start = i + j * block_len;
const block: Block = slice[start..][0..block_len].*;
matches[j] = block == mask;
}
const combined = matches[0] | matches[1] | matches[2] | matches[3];
if (@reduce(.Or, combined)) {
@branchHint(.unlikely);
if (std.simd.firstTrue(matches[0])) |find| return i + find;
if (std.simd.firstTrue(matches[1])) |find| return i + block_len + find;
if (std.simd.firstTrue(matches[2])) |find| return i + 2 * block_len + find;
return i + 3 * block_len + std.simd.firstTrue(matches[3]).?;
}
}
// {block_len, block_len / 2} check
inline for (0..2) |j| {
const block_x_len = block_len / (1 << j);
comptime if (block_x_len < 4) break;
while (i + block_len <= slice.len) : (i += block_len) {
const block: Block = slice[i..][0..block_len].*;
if (std.simd.firstTrue(block == mask)) |find| return i + find;
}
const BlockX = @Vector(block_x_len, T);
if (i + block_x_len < slice.len) {
const mask: BlockX = @splat(value);
const block: BlockX = slice[i..][0..block_x_len].*;
const matches = block == mask;
if (@reduce(.Or, matches)) {
return i + std.simd.firstTrue(matches).?;
}
i += block_x_len;
inline for (1..block_len) |j| {
const small_block_len = block_len / (2 * j);
comptime if (small_block_len < 4) break;
const SmallBlock = @Vector(small_block_len, T);
if (i + small_block_len <= slice.len) {
const small_mask: SmallBlock = @splat(value);
const block: SmallBlock = slice[i..][0..small_block_len].*;
const matches = block == small_mask;
if (std.simd.firstTrue(matches)) |find| return i + find;
i += small_block_len;
}
}
}