Function xo_retain_hash

tools/libxo/libxo/libxo.c:1371–1387

* Simple hash function based on Thomas Wang's paper. The original is * gone, but an archive is available on the Way Back Machine: * * http://web.archive.org/web/20071223173210/\ * http://www.concentric.net/~Ttwang/tech/inthash.htm * * For our purposes, we can assume the low four bits are uninteresting * since any string less that 16 bytes wouldn't be worthy of * retaining. We toss th

 * algorithm, and cap the result at RETAIN_HASH_SIZE.
 */
static unsigned
xo_retain_hash (const char *fmt)
{
    volatile uintptr_t iptr = (uintptr_t) (const void *) fmt;

    /* Discard low four bits and high bits; they aren't interesting */
    uint32_t val = (uint32_t) ((iptr >> 4) & (((1 << 24) - 1)));

    val = (val ^ 61) ^ (val >> 16);
    val = val + (val << 3);
    val = val ^ (val >> 4);
    val = val * 0x3a8f05c5;	/* My large prime number */
    val = val ^ (val >> 15);
    val &= RETAIN_HASH_SIZE - 1;

    return val;
}	

/*
 * Walk all buckets, clearing all retained entries