myMemset

#include <immintrin.h>
#include <stdint.h>

__attribute__((always_inline)) void* myMemset(void* Dst, int Val, size_t Size)
{
    void* first = Dst;
    __m256i ymm = _mm256_set1_epi8((uint8_t)Val);
    for (; Size >= 32; Size -= 32)
    {
        _mm256_storeu_si256((__m256i *)Dst, ymm);
        (uint8_t* &)Dst += 32;
    }
#if defined _M_X64 || defined _M_IA64 || defined __amd64
    const uint64_t temp = 0x0d101010101010101ULL * (uint8_t)Val;
#else
    const uint32_t temp = 0x0d1010101UL * (uint8_t)Val;
#endif
#define SET1B *((uint8_t*  &)Dst)++ = (uint8_t )temp
#define SET2B *((uint16_t* &)Dst)++ = (uint16_t)temp
#define SET4B *((uint32_t* &)Dst)++ = (uint32_t)temp
#if defined _M_X64 || defined _M_IA64 || defined __amd64
#   define SET8B *((uint64_t* &)Dst)++ = (uint64_t)temp
#else
#   define SET8B _mm_storel_epi64((__m128i *)Dst, _mm256_castsi256_si128(ymm)), ++(uint64_t* &)Dst
#endif
#define SET16B _mm_storeu_si128((__m128i *)Dst, _mm256_castsi256_si128(ymm)), ++(__m128i* &)Dst
    switch (Size)
    {
    case 0x00:                                          break;
    case 0x01:  SET1B;                                  break;
    case 0x02:          SET2B;                          break;
    case 0x03:  SET1B;  SET2B;                          break;
    case 0x04:  SET4B;                                  break;
    case 0x05:  SET1B;          SET4B;                  break;
    case 0x06:          SET2B;  SET4B;                  break;
    case 0x07:  SET1B;  SET2B;  SET4B;                  break;
    case 0x08:                          SET8B;          break;
    case 0x09:  SET1B;                  SET8B;          break;
    case 0x0A:          SET2B;          SET8B;          break;
    case 0x0B:  SET1B;  SET2B;          SET8B;          break;
    case 0x0C:                  SET4B;  SET8B;          break;
    case 0x0D:  SET1B;          SET4B;  SET8B;          break;
    case 0x0E:          SET2B;  SET4B;  SET8B;          break;
    case 0x0F:  SET1B;  SET2B;  SET4B;  SET8B;          break;
    case 0x10:                                  SET16B; break;
    case 0x11:  SET1B;                          SET16B; break;
    case 0x12:          SET2B;                  SET16B; break;
    case 0x13:  SET1B;  SET2B;                  SET16B; break;
    case 0x14:  SET4B;                          SET16B; break;
    case 0x15:  SET1B;          SET4B;          SET16B; break;
    case 0x16:          SET2B;  SET4B;          SET16B; break;
    case 0x17:  SET1B;  SET2B;  SET4B;          SET16B; break;
    case 0x18:                          SET8B;  SET16B; break;
    case 0x19:  SET1B;                  SET8B;  SET16B; break;
    case 0x1A:          SET2B;          SET8B;  SET16B; break;
    case 0x1B:  SET1B;  SET2B;          SET8B;  SET16B; break;
    case 0x1C:                  SET4B;  SET8B;  SET16B; break;
    case 0x1D:  SET1B;          SET4B;  SET8B;  SET16B; break;
    case 0x1E:          SET2B;  SET4B;  SET8B;  SET16B; break;
    case 0x1F:  SET1B;  SET2B;  SET4B;  SET8B;  SET16B; break;
    }
#undef SET1B
#undef SET2B
#undef SET4B
#undef SET8B
#undef SET16B
    return first;
}