__mo_lookup.c raw

   1  #include <stdint.h>
   2  #include <string.h>
   3  
   4  static inline uint32_t swapc(uint32_t x, int c)
   5  {
   6  	return c ? x>>24 | x>>8&0xff00 | x<<8&0xff0000 | x<<24 : x;
   7  }
   8  
   9  const char *__mo_lookup(const void *p, size_t size, const char *s)
  10  {
  11  	const uint32_t *mo = p;
  12  	int sw = *mo - 0x950412de;
  13  	uint32_t b = 0, n = swapc(mo[2], sw);
  14  	uint32_t o = swapc(mo[3], sw);
  15  	uint32_t t = swapc(mo[4], sw);
  16  	if (n>=size/4 || o>=size-4*n || t>=size-4*n || ((o|t)%4))
  17  		return 0;
  18  	o/=4;
  19  	t/=4;
  20  	for (;;) {
  21  		uint32_t ol = swapc(mo[o+2*(b+n/2)], sw);
  22  		uint32_t os = swapc(mo[o+2*(b+n/2)+1], sw);
  23  		if (os >= size || ol >= size-os || ((char *)p)[os+ol])
  24  			return 0;
  25  		int sign = strcmp(s, (char *)p + os);
  26  		if (!sign) {
  27  			uint32_t tl = swapc(mo[t+2*(b+n/2)], sw);
  28  			uint32_t ts = swapc(mo[t+2*(b+n/2)+1], sw);
  29  			if (ts >= size || tl >= size-ts || ((char *)p)[ts+tl])
  30  				return 0;
  31  			return (char *)p + ts;
  32  		}
  33  		else if (n == 1) return 0;
  34  		else if (sign < 0)
  35  			n /= 2;
  36  		else {
  37  			b += n/2;
  38  			n -= n/2;
  39  		}
  40  	}
  41  	return 0;
  42  }
  43