问为什么memcmp在仿生学中是这样的？

EN

 30 int memcmp(const void *s1, const void *s2, size_t n)
 31 {
 32     const unsigned char*  p1   = s1;
 33     const unsigned char*  end1 = p1 + n;
 34     const unsigned char*  p2   = s2;
 35     int                   d = 0;
 36 
 37     for (;;) {
 38         if (d || p1 >= end1) break;
 39         d = (int)*p1++ - (int)*p2++;
 40 
 41         if (d || p1 >= end1) break;
 42         d = (int)*p1++ - (int)*p2++;
 43 
 44         if (d || p1 >= end1) break;
 45         d = (int)*p1++ - (int)*p2++;
 46 
 47         if (d || p1 >= end1) break;
 48         d = (int)*p1++ - (int)*p2++;
 49     }
 50     return d;
 51 }