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Replace custom BitCount implementation with std::popcount (C++20)

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Aaron van Geffen
2024-07-12 14:30:55 +02:00
parent 6072545c0c
commit 6bea2e8190
4 changed files with 8 additions and 56 deletions
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50
src/openrct2/util/Util.cpp
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@@ -172,56 +172,6 @@ bool AVX2Available()
return false;
}
static bool BitCountPopcntAvailable()
{
#ifdef OPENRCT2_X86
// POPCNT support is declared as the 23rd bit of ECX with CPUID(EAX = 1).
uint32_t regs[4] = { 0 };
if (CPUIDX86(regs, 1))
{
return (regs[2] & (1 << 23));
}
#endif
return false;
}
static int32_t BitCountPopcnt(uint32_t source)
{
// Use CPUID defines to figure out calling style
#if defined(OpenRCT2_CPUID_GNUC_X86)
// use asm directly in order to actually emit the instruction : using
// __builtin_popcount results in an extra call to a library function.
int32_t rv;
asm volatile("popcnt %1,%0" : "=r"(rv) : "rm"(source) : "cc");
return rv;
#elif defined(OpenRCT2_CPUID_MSVC_X86)
return _mm_popcnt_u32(source);
#else
Guard::Fail("bitcount_popcnt() called, without support compiled in");
return INT_MAX;
#endif
}
static int32_t BitCountLut(uint32_t source)
{
// https://graphics.stanford.edu/~seander/bithacks.html
static constexpr uint8_t BitsSetTable256[256] = {
#define B2(n) n, (n) + 1, (n) + 1, (n) + 2
#define B4(n) B2(n), B2((n) + 1), B2((n) + 1), B2((n) + 2)
#define B6(n) B4(n), B4((n) + 1), B4((n) + 1), B4((n) + 2)
B6(0), B6(1), B6(1), B6(2)
};
return BitsSetTable256[source & 0xff] + BitsSetTable256[(source >> 8) & 0xff] + BitsSetTable256[(source >> 16) & 0xff]
+ BitsSetTable256[source >> 24];
}
static const auto BitCountFn = BitCountPopcntAvailable() ? BitCountPopcnt : BitCountLut;
int32_t BitCount(uint32_t source)
{
return BitCountFn(source);
}
/* Case insensitive logical compare */
// Example:
// - Guest 10