AK: Fix off by one error in integral ceil_log2()

Previously, certain values of `ceil_log2(x)` would be 1 smaller than `ceil(log2(x))`.
Author: https://github.com/tcl3 Commit: d0d81e470e Pull-request: https://github.com/SerenityOS/serenity/pull/24318 Reviewed-by: https://github.com/Hendiadyoin1 ✅
2025-09-05 09:06:08 +00:00 · 2024-05-13 18:57:38 +01:00 · 2024-05-13 18:57:38 +01:00 · d0d81e470e · 2024-07-18 01:43:16 +09:00
commit d0d81e470e
parent 29112f7365
2 changed files with 36 additions and 4 deletions
--- a/AK/IntegralMath.h
+++ b/AK/IntegralMath.h
@ -27,12 +27,10 @@ constexpr T log2(T x)
 template<Integral T>
 constexpr T ceil_log2(T x)
 {
-    if (!x)
+    if (x <= 1)
        return 0;

-    T log = AK::log2(x);
-    log += (x & ((((T)1) << (log - 1)) - 1)) != 0;
-    return log;
+    return AK::log2(x - 1) + 1;
 }

 template<Integral I>