C的奇特字符串复制功能

#define ngx_cpymem(dst, src, n)   (((u_char *) memcpy(dst, src, n)) + (n))

static ngx_inline u_char *
ngx_copy(u_char *dst, u_char *src, size_t len)
{
    if (len < 17) {

        while (len) {
            *dst++ = *src++;
            len--;
        }

        return dst;

    } else {
        return ngx_cpymem(dst, src, len);
    }
}

/*
 * the simple inline cycle copies the variable length strings up to 16
 * bytes faster than icc8 autodetecting _intel_fast_memcpy()
 */

#if ( __INTEL_COMPILER >= 800 )

ngx_cpymem

#define ngx_copy                  ngx_cpymem

/*
 * gcc3, msvc, and icc7 compile memcpy() to the inline \"rep movs\".
 * gcc3 compiles memcpy(d, s, 4) to the inline \"mov\"es.
 * icc8 compile memcpy(d, s, 4) to the inline \"mov\"es or XMM moves.
 */