Optimized bit functions, added intrinsics for GCC and Clang
Code by @medranSolus
diff --git a/include/vk_mem_alloc.h b/include/vk_mem_alloc.h
index 97e321c..c03fe85 100644
--- a/include/vk_mem_alloc.h
+++ b/include/vk_mem_alloc.h
@@ -3064,12 +3064,18 @@
// Returns number of bits set to 1 in (v).
static inline uint32_t VmaCountBitsSet(uint32_t v)
{
+#ifdef _MSC_VER
+ return __popcnt(v);
+#elif defined __GNUC__ || defined __clang__
+ return static_cast<uint32_t>(__builtin_popcount(v));
+#else
uint32_t c = v - ((v >> 1) & 0x55555555);
c = ((c >> 2) & 0x33333333) + (c & 0x33333333);
c = ((c >> 4) + c) & 0x0F0F0F0F;
c = ((c >> 8) + c) & 0x00FF00FF;
c = ((c >> 16) + c) & 0x0000FFFF;
return c;
+#endif
}
static inline uint8_t VmaBitScanLSB(uint64_t mask)
@@ -3078,15 +3084,20 @@
unsigned long pos;
if (_BitScanForward64(&pos, mask))
return static_cast<uint8_t>(pos);
+ return UINT8_MAX;
+#elif defined __GNUC__ || defined __clang__
+ return static_cast<uint8_t>__builtin_ffsll(mask)) - 1U;
#else
uint8_t pos = 0;
+ uint64_t bit = 1;
do
{
- if (mask & (1ULL << pos))
+ if (mask & bit)
return pos;
+ bit <<= 1;
} while (pos++ < 63);
-#endif
return UINT8_MAX;
+#endif
}
static inline uint8_t VmaBitScanLSB(uint32_t mask)
@@ -3095,15 +3106,20 @@
unsigned long pos;
if (_BitScanForward(&pos, mask))
return static_cast<uint8_t>(pos);
+ return UINT8_MAX;
+#elif defined __GNUC__ || defined __clang__
+ return static_cast<uint8_t>__builtin_ffsl(mask)) - 1U;
#else
uint8_t pos = 0;
+ uint32_t bit = 1;
do
{
- if (mask & (1UL << pos))
+ if (mask & bit)
return pos;
+ bit <<= 1;
} while (pos++ < 31);
-#endif
return UINT8_MAX;
+#endif
}
static inline uint8_t VmaBitScanMSB(uint64_t mask)
@@ -3112,12 +3128,17 @@
unsigned long pos;
if (_BitScanReverse64(&pos, mask))
return static_cast<uint8_t>(pos);
+#elif defined __GNUC__ || defined __clang__
+ if (mask)
+ return static_cast<uint8_t>(__builtin_clzll(mask));
#else
uint8_t pos = 63;
+ uint64_t bit = 1 << 63;
do
{
- if (mask & (1ULL << pos))
+ if (mask & bit)
return pos;
+ bit >>= 1;
} while (pos-- > 0);
#endif
return UINT8_MAX;
@@ -3129,12 +3150,17 @@
unsigned long pos;
if (_BitScanReverse(&pos, mask))
return static_cast<uint8_t>(pos);
+#elif defined __GNUC__ || defined __clang__
+ if (mask)
+ return static_cast<uint8_t>(__builtin_clzl(mask));
#else
uint8_t pos = 31;
+ uint32_t bit = 1 << 31;
do
{
- if (mask & (1UL << pos))
+ if (mask & bit)
return pos;
+ bit >>= 1;
} while (pos-- > 0);
#endif
return UINT8_MAX;
