From 8ddce90e62e52244b7f6d1104bb39a55350f0a83 Mon Sep 17 00:00:00 2001
From: CrazyboyQCD <53971641+CrazyboyQCD@users.noreply.github.com>
Date: Sat, 14 Sep 2024 08:22:19 +0800
Subject: [PATCH] `std.ascii`: make `toLower` `toUpper` branchless (#21369)

Co-authored-by: WX\shixi <shixi1@cnwxsoft.com>
---
 lib/std/ascii.zig | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/lib/std/ascii.zig b/lib/std/ascii.zig
index d5b028500f..7b99f6f4cf 100644
--- a/lib/std/ascii.zig
+++ b/lib/std/ascii.zig
@@ -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;
 }
 
 /// 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" {