From 1ffae59fec60816ff364b4ade93c6fc2fc1571cf Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Fri, 7 Feb 2025 00:47:43 -0800
Subject: [PATCH] std.heap.SmpAllocator: fix using wrong size class indices

---
 lib/std/heap/SmpAllocator.zig | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/lib/std/heap/SmpAllocator.zig b/lib/std/heap/SmpAllocator.zig
index b4e7138291..c1c9ca5517 100644
--- a/lib/std/heap/SmpAllocator.zig
+++ b/lib/std/heap/SmpAllocator.zig
@@ -215,13 +215,11 @@ fn free(context: *anyopaque, memory: []u8, alignment: mem.Alignment, ra: usize)
 
 fn sizeClassIndex(len: usize, alignment: mem.Alignment) usize {
     return @max(
-        @bitSizeOf(usize) - @clz(len - 1),
-        @intFromEnum(alignment),
-        min_class,
-    );
+        @bitSizeOf(usize) - @clz(len + (@sizeOf(usize) - 1)),
+        @intFromEnum(alignment) + 1,
+    ) - min_class;
 }
 
 fn slotSize(class: usize) usize {
-    const Log2USize = std.math.Log2Int(usize);
-    return @as(usize, 1) << @as(Log2USize, @intCast(class));
+    return @as(usize, 1) << @intCast(class + min_class);
 }