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getenvW: Take advantage of sliceTo/indexOfScalarPos optimizations

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Both sliceTo and indexOfScalarPos use SIMD when available to speed up the search. On my x86_64 machine, this leads to getenvW being around 2-3x faster overall.

Additionally, any future improvements to sliceTo/indexOfScalarPos will benefit getenvW.
This commit is contained in:
Ryan Liptak 2025-03-16 17:37:31 -07:00
parent 78ecf3bb3a
commit 66dcebcc76
1 changed files with 15 additions and 13 deletions
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28
lib/std/process.zig
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@ -527,31 +527,33 @@ pub fn getenvW(key: [*:0]const u16) ?[:0]const u16 {
@compileError("Windows-only");
}
const key_slice = mem.sliceTo(key, 0);
// '=' anywhere but the start makes this an invalid environment variable name
if (key_slice.len > 0 and std.mem.indexOfScalar(u16, key_slice[1..], '=') != null) {
return null;
}
const ptr = windows.peb().ProcessParameters.Environment;
var i: usize = 0;
while (ptr[i] != 0) {
const key_start = i;
const key_value = mem.sliceTo(ptr[i..], 0);
// There are some special environment variables that start with =,
// so we need a special case to not treat = as a key/value separator
// if it's the first character.
// https://devblogs.microsoft.com/oldnewthing/20100506-00/?p=14133
if (ptr[key_start] == '=') i += 1;
while (ptr[i] != 0 and ptr[i] != '=') : (i += 1) {}
const this_key = ptr[key_start..i];
if (ptr[i] == '=') i += 1;
const value_start = i;
while (ptr[i] != 0) : (i += 1) {}
const this_value = ptr[value_start..i :0];
const equal_search_start: usize = if (key_value[0] == '=') 1 else 0;
const equal_index = std.mem.indexOfScalarPos(u16, key_value, equal_search_start, '=') orelse {
// This is enforced by CreateProcess.
// If violated, CreateProcess will fail with INVALID_PARAMETER.
unreachable; // must contain a =
};
const this_key = key_value[0..equal_index];
if (windows.eqlIgnoreCaseWTF16(key_slice, this_key)) {
return this_value;
return key_value[equal_index + 1 ..];
}
i += 1; // skip over null byte
// skip past the NUL terminator
i += key_value.len + 1;
}
return null;
}