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std.ascii: make toLower toUpper branchless #21369

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Merged
merged 3 commits into from
Sep 14, 2024
Merged

std.ascii: make toLower toUpper branchless #21369

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30c443a
chore: make `toLower` `toUpper` branchless
Sep 10, 2024
b5d3b56
chore: use `*%` to avoid overflow check to optimize debug codegen
Sep 11, 2024
f118b5a
chore: use shift operation for better readability
Sep 13, 2024
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14 changes: 4 additions & 10 deletions lib/std/ascii.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -182,20 +182,14 @@ pub const isASCII = isAscii;

/// Uppercases the character and returns it as-is if already uppercase or not a letter.
pub fn toUpper(c: u8) u8 {
if (isLower(c)) {
return c & 0b11011111;
} else {
return c;
}
const mask = @as(u8, @intFromBool(isLower(c))) << 5;
return c ^ mask;
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Shouldn't this be &, rather than ^ (xor)? As is it would toggle the case, which isn't what the function is supposed to do (both by convention and according to doc comment)

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xor looks correct -- you're right that it toggles the case, but only when isLower(c) is true

}

/// Lowercases the character and returns it as-is if already lowercase or not a letter.
pub fn toLower(c: u8) u8 {
if (isUpper(c)) {
return c | 0b00100000;
} else {
return c;
}
const mask = @as(u8, @intFromBool(isUpper(c))) << 5;
return c | mask;
}

test "ASCII character classes" {
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