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Removed usage of __popcnt

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Apparently some old processors don't support this instruction. It's up to the user to provide optimized implementation by defining macro VMA_COUNT_BITS_SET.

Fixes #245
This commit is contained in:
Adam Sawicki 2022-02-25 13:51:13 +01:00
parent dc3f6bb915
commit 88bf8cb9a8
1 changed files with 22 additions and 10 deletions
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30
include/vk_mem_alloc.h
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@ -2685,6 +2685,11 @@ static void vma_aligned_free(void* VMA_NULLABLE ptr)
#endif
#endif
#ifndef VMA_COUNT_BITS_SET
// Returns number of bits set to 1 in (v)
#define VMA_COUNT_BITS_SET(v) VmaCountBitsSet(v)
#endif
#ifndef VMA_BITSCAN_LSB
// Scans integer for index of first nonzero value from the Least Significant Bit (LSB). If mask is 0 then returns UINT8_MAX
#define VMA_BITSCAN_LSB(mask) VmaBitScanLSB(mask)
@ -3074,21 +3079,28 @@ class VmaAllocationObjectAllocator;
#ifndef _VMA_FUNCTIONS
// Returns number of bits set to 1 in (v).
/*
Returns number of bits set to 1 in (v).
On specific platforms and compilers you can use instrinsics like:
Visual Studio:
return __popcnt(v);
GCC, Clang:
return static_cast<uint32_t>(__builtin_popcount(v));
Define macro VMA_COUNT_BITS_SET to provide your optimized implementation.
But you need to check in runtime whether user's CPU supports these, as some old processors don't.
*/
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)
@ -14625,8 +14637,8 @@ VkResult VmaAllocator_T::FindMemoryTypeIndex(
if((requiredFlags & ~currFlags) == 0)
{
// Calculate cost as number of bits from preferredFlags not present in this memory type.
uint32_t currCost = VmaCountBitsSet(preferredFlags & ~currFlags) +
VmaCountBitsSet(currFlags & notPreferredFlags);
uint32_t currCost = VMA_COUNT_BITS_SET(preferredFlags & ~currFlags) +
VMA_COUNT_BITS_SET(currFlags & notPreferredFlags);
// Remember memory type with lowest cost.
if(currCost < minCost)
{