用neon写memcopy

以下是使用NEON指令集编写的memcopy代码示例：

void neon_memcpy(void* dst, const void* src, size_t size)
{
    // Round down the size to the nearest multiple of 16
    size_t size_rounded = size & ~0xF;

    // Cast the source and destination pointers to the appropriate types
    uint8_t* dst_ptr = (uint8_t*)dst;
    const uint8_t* src_ptr = (const uint8_t*)src;

    // Use NEON to copy blocks of 16 bytes at a time
    for (size_t i = 0; i < size_rounded; i += 16) {
        asm volatile (
            "vld1.8 {d0-d1}, [%[src_ptr]]! \n"
            "vst1.8 {d0-d1}, [%[dst_ptr]]! \n"
            : [dst_ptr] "+r" (dst_ptr),
              [src_ptr] "+r" (src_ptr)
            :
            : "d0", "d1"
        );
    }

    // Copy any remaining bytes using a simple loop
    for (size_t i = size_rounded; i < size; i++) {
        *dst_ptr++ = *src_ptr++;
    }
}

该函数使用NEON指令集来复制内存块。它首先将要复制的大小舍入到最近的16字节倍数，然后使用NEON指令集来复制块大小为16字节的块。对于任何剩余的字节，函数使用简单的循环来复制它们。