+ unsigned char *dest = (void *)&id->val;
+ unsigned int accum = 0;
+ unsigned char dnum = sizeof(id->val);
+
+ memset(id, 0, sizeof(*id));
+ id->ptr = ptr;
+ if (sizeof(id->val) >= sizeof(id->ptr))
+ {
+ /* 'ptr' can be embedded in 'val' without loss of uniqueness */
+ id->val = (unsigned long)id->ptr;
+ return;
+ }
+ /* hash ptr ==> val. Each byte of 'val' gets the mod-256 total of a
+ * linear function over the bytes in 'ptr', the co-efficients of which
+ * are a sequence of low-primes (hash_coeffs is an 8-element cycle) -
+ * the starting prime for the sequence varies for each byte of 'val'
+ * (unique polynomials unless pointers are >64-bit). For added spice,
+ * the totals accumulate rather than restarting from zero, and the index
+ * of the 'val' byte is added each time (position dependence). If I was
+ * a black-belt, I'd scan big-endian pointers in reverse to give
+ * low-order bits more play, but this isn't crypto and I'd prefer nobody
+ * mistake it as such. Plus I'm lazy. */
+ while (dnum--)
+ {
+ const unsigned char *src = (void *)&id->ptr;
+ unsigned char snum = sizeof(id->ptr);
+ while (snum--)
+ accum += *(src++) * hash_coeffs[(snum + dnum) & 7];
+ accum += dnum;
+ *(dest++) = accum & 255;
+ }