使用SSE指令集优化memcpy

#include 
#include 
/**
 * Copy 16 bytes from one location to another using optimised SSE
 * instructions. The locations should not overlap.
 *
 * @param s1
 *   Pointer to the destination of the data.
 * @param s2
 *   Pointer to the source data.
 */
static inline void
mov16(uint8_t *dst, const uint8_t *src)
{
	asm volatile ("movdqu (%[src]), %%xmm0\n\t"
		      "movdqu %%xmm0, (%[dst])\n\t"
		      :
		      : [src] "r" (src),
			[dst] "r"(dst)
		      : "xmm0", "memory");
}

/**
 * Copy 32 bytes from one location to another using optimised SSE
 * instructions. The locations should not overlap.
 *
 * @param s1
 *   Pointer to the destination of the data.
 * @param s2
 *   Pointer to the source data.
 */
static inline void
mov32(uint8_t *dst, const uint8_t *src)
{
	asm volatile ("movdqu (%[src]), %%xmm0\n\t"
		      "movdqu 16(%[src]), %%xmm1\n\t"
		      "movdqu %%xmm0, (%[dst])\n\t"
		      "movdqu %%xmm1, 16(%[dst])"
		      :
		      : [src] "r" (src),
			[dst] "r"(dst)
		      : "xmm0", "xmm1", "memory");
}

/**
 * Copy 48 bytes from one location to another using optimised SSE
 * instructions. The locations should not overlap.
 *
 * @param s1
 *   Pointer to the destination of the data.
 * @param s2
 *   Pointer to the source data.
 */
static inline void
mov48(uint8_t *dst, const uint8_t *src)
{
	asm volatile ("movdqu (%[src]), %%xmm0\n\t"
		      "movdqu 16(%[src]), %%xmm1\n\t"
		      "movdqu 32(%[src]), %%xmm2\n\t"
		      "movdqu %%xmm0, (%[dst])\n\t"
		      "movdqu %%xmm1, 16(%[dst])"
		      "movdqu %%xmm2, 32(%[dst])"
		      :
		      : [src] "r" (src),
			[dst] "r"(dst)
		      : "xmm0", "xmm1", "memory");
}

/**
 * Copy 64 bytes from one location to another using optimised SSE
 * instructions. The locations should not overlap.
 *
 * @param s1
 *   Pointer to the destination of the data.
 * @param s2
 *   Pointer to the source data.
 */
static inline void
mov64(uint8_t *dst, const uint8_t *src)
{
	asm volatile ("movdqu (%[src]), %%xmm0\n\t"
		      "movdqu 16(%[src]), %%xmm1\n\t"
		      "movdqu 32(%[src]), %%xmm2\n\t"
		      "movdqu 48(%[src]), %%xmm3\n\t"
		      "movdqu %%xmm0, (%[dst])\n\t"
		      "movdqu %%xmm1, 16(%[dst])\n\t"
		      "movdqu %%xmm2, 32(%[dst])\n\t"
		      "movdqu %%xmm3, 48(%[dst])"
		      :
		      : [src] "r" (src),
			[dst] "r"(dst)
		      : "xmm0", "xmm1", "xmm2", "xmm3","memory");
}

/**
 * Copy 128 bytes from one location to another using optimised SSE
 * instructions. The locations should not overlap.
 *
 * @param s1
 *   Pointer to the destination of the data.
 * @param s2
 *   Pointer to the source data.
 */
static inline void
mov128(uint8_t *dst, const uint8_t *src)
{
	asm volatile ("movdqu (%[src]), %%xmm0\n\t"
		      "movdqu 16(%[src]), %%xmm1\n\t"
		      "movdqu 32(%[src]), %%xmm2\n\t"
		      "movdqu 48(%[src]), %%xmm3\n\t"
		      "movdqu 64(%[src]), %%xmm4\n\t"
		      "movdqu 80(%[src]), %%xmm5\n\t"
		      "movdqu 96(%[src]), %%xmm6\n\t"
		      "movdqu 112(%[src]), %%xmm7\n\t"
		      "movdqu %%xmm0, (%[dst])\n\t"
		      "movdqu %%xmm1, 16(%[dst])\n\t"
		      "movdqu %%xmm2, 32(%[dst])\n\t"
		      "movdqu %%xmm3, 48(%[dst])\n\t"
		      "movdqu %%xmm4, 64(%[dst])\n\t"
		      "movdqu %%xmm5, 80(%[dst])\n\t"
		      "movdqu %%xmm6, 96(%[dst])\n\t"
		      "movdqu %%xmm7, 112(%[dst])"
		      :
		      : [src] "r" (src),
			[dst] "r"(dst)
		      : "xmm0", "xmm1", "xmm2", "xmm3",
			"xmm4", "xmm5", "xmm6", "xmm7", "memory");
}

/**
 * Copy 256 bytes from one location to another using optimised SSE
 * instructions. The locations should not overlap.
 *
 * @param s1
 *   Pointer to the destination of the data.
 * @param s2
 *   Pointer to the source data.
 */
static inline void
mov256(uint8_t *dst, const uint8_t *src)
{
	/*
	 * There are 16XMM registers, but this function does not use
	 * them all so that it can still be compiled as 32bit
	 * code. The performance increase was neglible if all 16
	 * registers were used.
	 */
	mov128(dst, src);
	mov128(dst + 128, src + 128);
}


/**
 * Copy bytes from one location to another. The locations should not overlap.
 *
 * @param s1
 *   Pointer to the destination of the data.
 * @param s2
 *   Pointer to the source data.
 * @param n
 *   Number of bytes to copy.
 * @return
 *   s1
 */
void *
fast_memcpy(void *s1, const void *s2, size_t n)
{
	uint8_t *dst = (uint8_t *)s1;
	const uint8_t *src = (const uint8_t *)s2;

	/* We can't copy < 16 bytes using XMM registers so do it manually. */
	if (n < 16) {
		if (n & 0x01) {
			*dst = *src;
			dst += 1;
			src += 1;
		}
		if (n & 0x02) {
			*(uint16_t *)dst = *(const uint16_t *)src;
			dst += 2;
			src += 2;
		}
		if (n & 0x04) {
			*(uint32_t *)dst = *(const uint32_t *)src;
			dst += 4;
			src += 4;
		}
		if (n & 0x08) {
			*(uint64_t *)dst = *(const uint64_t *)src;
		}
		return dst;
	}

	/* Special fast cases for <= 128 bytes */
	if (n <= 32) {
		mov16(dst, src);
		mov16(dst - 16 + n, src - 16 + n);
		return s1;
	}
	if (n <= 64) {
		mov32(dst, src);
		mov32(dst - 32 + n, src - 32 + n);
		return s1;
	}
	if (n <= 128) {
		mov64(dst, src);
		mov64(dst - 64 + n, src - 64 + n);
		return s1;
	}

	/*
	 * For large copies > 128 bytes. This combination of 256, 64 and 16 byte
	 * copies was found to be faster than doing 128 and 32 byte copies as
	 * well.
	 */
	for (; n >= 256; n -= 256, dst += 256, src += 256) {
		mov256(dst, src);
	}

	/*
	 * We split the remaining bytes (which will be less than 256) into
	 * 64byte (2^6) chunks.
	 * Using incrementing integers in the case labels of a switch statement
	 * enourages the compiler to use a jump table. To get incrementing
	 * integers, we shift the 2 relevant bits to the LSB position to first
	 * get decrementing integers, and then subtract.
	 */
	switch (3 - (n >> 6)) {
	case 0x00:
		mov64(dst, src);
		n -= 64;
		dst += 64;
		src += 64;       /* fallthrough */
	case 0x01:
		mov64(dst, src);
		n -= 64;
		dst += 64;
		src += 64;       /* fallthrough */
	case 0x02:
		mov64(dst, src);
		n -= 64;
		dst += 64;
		src += 64;       /* fallthrough */
	default:
		;
	}

	/*
	 * We split the remaining bytes (which will be less than 64) into
	 * 16byte (2^4) chunks, using the same switch structure as above.
	 */
	switch (3 - (n >> 4)) {
	case 0x00:
		mov16(dst, src);
		n -= 16;
		dst += 16;
		src += 16;       /* fallthrough */
	case 0x01:
		mov16(dst, src);
		n -= 16;
		dst += 16;
		src += 16;       /* fallthrough */
	case 0x02:
		mov16(dst, src);
		n -= 16;
		dst += 16;
		src += 16;       /* fallthrough */
	default:
		;
	}

	/* Copy any remaining bytes, without going beyond end of buffers */
	if (n != 0) {
		mov16(dst - 16 + n, src - 16 + n);
	}
	return s1;
}

uint8_t src[1024] = {0};
uint8_t dst[1024] = {0};

int main(int argc, char **argv)
{
	fast_memcpy(dst, src, 1024);
	return 0;
}