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[Base] Fix math.h portability: use __builtin_ffs and fix lzcnt narrowing

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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.
This commit is contained in:
Herman S.
2026-03-26 16:25:22 +09:00
parent 0bd565eade
commit 3efc88abbb
1 changed files with 11 additions and 3 deletions
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14
src/xenia/base/math.h
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@@ -296,7 +296,7 @@ inline bool bit_scan_forward(uint64_t v, uint32_t* out_first_set_index) {
} }
#else #else
inline bool bit_scan_forward(uint32_t v, uint32_t* out_first_set_index) { 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; *out_first_set_index = i - 1;
return i != 0; return i != 0;
} }
@@ -315,11 +315,19 @@ inline bool bit_scan_forward(int64_t v, uint32_t* out_first_set_index) {
template <typename T> template <typename T>
inline T log2_floor(T v) { 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> template <typename T>
inline T log2_ceil(T v) { 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> template <typename T>