AVX2 feature detection

[dmex]

The CRT has feature detection for AVX before calling winmain and this code duplicates the CRT:

HexCtrl/HexCtrl/src/HexUtility.ixx

Lines 143 to 154 in 1bbfffa

	[[nodiscard]] bool HasAVX2() {
	const static bool fHasAVX2 = []() {
	int arrInfo[4] { };
	__cpuid(arrInfo, 0);
	if (arrInfo[0] >= 7) {
	__cpuid(arrInfo, 7);
	return (arrInfo[1] & (1 << 5)) != 0;
	}
	return false;
	}();
	return fHasAVX2;
	}

You can include the isa_availability header and just check the flags:

#include <isa_availability.h>

extern int __isa_available;
#define ISA_AVAILABLE_X86 0
#define ISA_AVAILABLE_SSE2 1
#define ISA_AVAILABLE_SSE42 2
#define ISA_AVAILABLE_AVX 3
#define ISA_AVAILABLE_ENFSTRG 4
#define ISA_AVAILABLE_AVX2 5
#define ISA_AVAILABLE_AVX512 6

extern long __isa_enabled;
#define ISA_ENABLED_X86 0x00000001
#define ISA_ENABLED_SSE2 0x00000002
#define ISA_ENABLED_SSE42 0x00000004
#define ISA_ENABLED_AVX 0x00000008
#define ISA_ENABLED_ENFSTRG 0x00000010
#define ISA_ENABLED_AVX2 0x00000020
#define ISA_ENABLED_AVX512 0x00000040

Example usage (from the STL: https://github.com/microsoft/STL/blob/main/stl/src/vector_algorithms.cpp)

bool _Use_avx2() noexcept {
    return __isa_enabled & (1 << __ISA_AVAILABLE_AVX2);
}

[jovibor]

Well, you're absolutely right.
Except that this header is not standard compliant, and may be a subject to change in the future, see here.
Also, this header was replaced in the STL internal usages recently by the <__msvc_bit_utils.hpp> helper header, see here and here.
Also, it's one more additional dependency, which I would rather avoid.
And eventually, it's just a matter of preference.