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add thomas wang's integer hash function; use it for hashq, hashv

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* libguile/hash.c (scm_raw_ihashq): Add Thomas Wang's integer hash
  function, from http://www.cris.com/~Ttwang/tech/inthash.htm.
  (scm_ihashq, scm_ihashv): Use it here.
This commit is contained in:
Andy Wingo 2011-10-26 00:37:24 +02:00
parent 7914b2b069
commit 71f89dd7e9
1 changed files with 30 additions and 3 deletions
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33
libguile/hash.c
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@ -224,6 +224,34 @@ scm_i_utf8_string_hash (const char *str, size_t len)
}
/* Thomas Wang's integer hasher, from
http://www.cris.com/~Ttwang/tech/inthash.htm. */
static unsigned long
scm_raw_ihashq (scm_t_bits key)
{
if (sizeof (key) < 8)
{
key = (key ^ 61) ^ (key >> 16);
key = key + (key << 3);
key = key ^ (key >> 4);
key = key * 0x27d4eb2d;
key = key ^ (key >> 15);
}
else
{
key = (~key) + (key << 21); // key = (key << 21) - key - 1;
key = key ^ (key >> 24);
key = (key + (key << 3)) + (key << 8); // key * 265
key = key ^ (key >> 14);
key = (key + (key << 2)) + (key << 4); // key * 21
key = key ^ (key >> 28);
key = key + (key << 31);
}
key >>= 2; /* Ensure that it fits in a fixnum. */
return key;
}
/* Dirk:FIXME:: why downcase for characters? (2x: scm_hasher, scm_ihashv) */
/* Dirk:FIXME:: scm_hasher could be made static. */
@ -345,11 +373,10 @@ scm_hasher(SCM obj, unsigned long n, size_t d)
unsigned long
scm_ihashq (SCM obj, unsigned long n)
{
return (SCM_UNPACK (obj) >> 1) % n;
return scm_raw_ihashq (SCM_UNPACK (obj)) % n;
}
@ -385,7 +412,7 @@ scm_ihashv (SCM obj, unsigned long n)
if (SCM_NUMP(obj))
return (unsigned long) scm_hasher(obj, n, 10);
else
return SCM_UNPACK (obj) % n;
return scm_raw_ihashq (SCM_UNPACK (obj)) % n;
}