From 3efc88abbb6237f13859cf5ceb535e1a54a3003c Mon Sep 17 00:00:00 2001
From: "Herman S." <429230+has207@users.noreply.github.com>
Date: Thu, 26 Mar 2026 16:25:22 +0900
Subject: [PATCH] [Base] Fix math.h portability: use __builtin_ffs and fix
 lzcnt narrowing

ffs() can collide with POSIX macro definitions on some platforms;
__builtin_ffs is the portable GCC/Clang intrinsic. log2_floor/log2_ceil
passed template types directly to lzcnt which has only uint32_t and
uint64_t overloads, causing implicit narrowing on smaller types.
---
 src/xenia/base/math.h | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/xenia/base/math.h b/src/xenia/base/math.h
index becb8a6a7..116f85b09 100644
--- a/src/xenia/base/math.h
+++ b/src/xenia/base/math.h
@@ -296,7 +296,7 @@ inline bool bit_scan_forward(uint64_t v, uint32_t* out_first_set_index) {
 }
 #else
 inline bool bit_scan_forward(uint32_t v, uint32_t* out_first_set_index) {
-  int i = ffs(v);
+  int i = __builtin_ffs(v);
   *out_first_set_index = i - 1;
   return i != 0;
 }
@@ -315,11 +315,19 @@ inline bool bit_scan_forward(int64_t v, uint32_t* out_first_set_index) {
 
 template <typename T>
 inline T log2_floor(T v) {
-  return sizeof(T) * 8 - 1 - lzcnt(v);
+  if constexpr (sizeof(T) <= sizeof(uint32_t)) {
+    return sizeof(T) * 8 - 1 - lzcnt(static_cast<uint32_t>(v));
+  } else {
+    return sizeof(T) * 8 - 1 - lzcnt(static_cast<uint64_t>(v));
+  }
 }
 template <typename T>
 inline T log2_ceil(T v) {
-  return sizeof(T) * 8 - lzcnt(v - 1);
+  if constexpr (sizeof(T) <= sizeof(uint32_t)) {
+    return sizeof(T) * 8 - lzcnt(static_cast<uint32_t>(v - 1));
+  } else {
+    return sizeof(T) * 8 - lzcnt(static_cast<uint64_t>(v - 1));
+  }
 }
 
 template <typename T>