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40x faster .toString('hex') (#4237)

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Co-authored-by: Jarred Sumner <709451+Jarred-Sumner@users.noreply.github.com>
This commit is contained in:
Jarred Sumner
2023-08-21 08:31:17 -07:00
committed by GitHub
parent 1b8f569792
commit def5a85d90
3 changed files with 105 additions and 17 deletions
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79
src/string_immutable.zig
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@@ -3602,6 +3602,14 @@ inline fn _decodeHexToBytes(destination: []u8, comptime Char: type, source: []co
return destination.len - remain.len;
}
fn byte2hex(char: u8) u8 {
return switch (char) {
0...9 => char + '0',
10...15 => char - 10 + 'a',
else => unreachable,
};
}
pub fn encodeBytesToHex(destination: []u8, source: []const u8) usize {
if (comptime Environment.allow_assert) {
std.debug.assert(destination.len > 0);
@@ -3614,10 +3622,75 @@ pub fn encodeBytesToHex(destination: []u8, source: []const u8) usize {
const to_read = to_write / 2;
const formatter = std.fmt.fmtSliceHexLower(source[0..to_read]);
const written = std.fmt.bufPrint(destination, "{}", .{formatter}) catch unreachable;
var remaining = source[0..to_read];
var remaining_dest = destination;
if (comptime Environment.enableSIMD) {
var remaining_end = remaining.ptr + remaining.len - (remaining.len % 16);
while (remaining.ptr != remaining_end) {
const input_chunk: @Vector(16, u8) = remaining[0..16].*;
const input_chunk_4: @Vector(16, u8) = input_chunk >> @as(@Vector(16, u8), @splat(@as(u8, 4)));
const input_chunk_15: @Vector(16, u8) = input_chunk & @as(@Vector(16, u8), @splat(@as(u8, 15)));
return written.len;
// This looks extremely redundant but it was the easiest way to make the compiler do the right thing
// the more convienient "0123456789abcdef" string produces worse codegen
// https://zig.godbolt.org/z/bfdracEeq
const lower_16 = [16]u8{
byte2hex(input_chunk_4[0]),
byte2hex(input_chunk_4[1]),
byte2hex(input_chunk_4[2]),
byte2hex(input_chunk_4[3]),
byte2hex(input_chunk_4[4]),
byte2hex(input_chunk_4[5]),
byte2hex(input_chunk_4[6]),
byte2hex(input_chunk_4[7]),
byte2hex(input_chunk_4[8]),
byte2hex(input_chunk_4[9]),
byte2hex(input_chunk_4[10]),
byte2hex(input_chunk_4[11]),
byte2hex(input_chunk_4[12]),
byte2hex(input_chunk_4[13]),
byte2hex(input_chunk_4[14]),
byte2hex(input_chunk_4[15]),
};
const upper_16 = [16]u8{
byte2hex(input_chunk_15[0]),
byte2hex(input_chunk_15[1]),
byte2hex(input_chunk_15[2]),
byte2hex(input_chunk_15[3]),
byte2hex(input_chunk_15[4]),
byte2hex(input_chunk_15[5]),
byte2hex(input_chunk_15[6]),
byte2hex(input_chunk_15[7]),
byte2hex(input_chunk_15[8]),
byte2hex(input_chunk_15[9]),
byte2hex(input_chunk_15[10]),
byte2hex(input_chunk_15[11]),
byte2hex(input_chunk_15[12]),
byte2hex(input_chunk_15[13]),
byte2hex(input_chunk_15[14]),
byte2hex(input_chunk_15[15]),
};
const output_chunk = std.simd.interlace(.{
lower_16,
upper_16,
});
remaining_dest[0..32].* = @bitCast(output_chunk);
remaining_dest = remaining_dest[32..];
remaining = remaining[16..];
}
}
for (remaining) |c| {
const charset = "0123456789abcdef";
const buf: [2]u8 = .{ charset[c >> 4], charset[c & 15] };
remaining_dest[0..2].* = buf;
remaining_dest = remaining_dest[2..];
}
return to_read * 2;
}
test "decodeHexToBytes" {