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Fix hashing of vectors to run in bounded time.

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* libguile/hash.c (SCM_MIN): New macro.
  (scm_hasher): In vector case, do nothing if d is 0.  Make sure to
  recurse with a reduced d.  Move the loop out of the 'if'.
This commit is contained in:
Mark H Weaver 2014-01-11 10:18:40 -05:00
parent 0e18163366
commit cc1cd04f81
1 changed files with 30 additions and 26 deletions
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56
libguile/hash.c
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@ -1,5 +1,5 @@
/* Copyright (C) 1995, 1996, 1997, 2000, 2001, 2003, 2004, 2006, 2008,
* 2009, 2010, 2011, 2012 Free Software Foundation, Inc.
* 2009, 2010, 2011, 2012, 2014 Free Software Foundation, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
@ -45,6 +45,7 @@
extern double floor();
#endif
#define SCM_MIN(A, B) ((A) < (B) ? (A) : (B))
unsigned long
scm_string_hash (const unsigned char *str, size_t len)
@ -228,31 +229,34 @@ scm_hasher(SCM obj, unsigned long n, size_t d)
return scm_i_struct_hash (obj, n, d);
case scm_tc7_wvect:
case scm_tc7_vector:
{
size_t len = SCM_SIMPLE_VECTOR_LENGTH (obj);
if (len > 5)
{
size_t i = d/2;
unsigned long h = 1;
while (i--)
{
SCM elt = SCM_SIMPLE_VECTOR_REF (obj, h % len);
h = ((h << 8) + (scm_hasher (elt, n, 2))) % n;
}
return h;
}
else
{
size_t i = len;
unsigned long h = (n)-1;
while (i--)
{
SCM elt = SCM_SIMPLE_VECTOR_REF (obj, h % len);
h = ((h << 8) + (scm_hasher (elt, n, d/len))) % n;
}
return h;
}
}
if (d > 0)
{
size_t len, i, d2;
unsigned long h;
len = SCM_SIMPLE_VECTOR_LENGTH (obj);
if (len > 5)
{
i = d / 2;
h = 1;
d2 = SCM_MIN (2, d - 1);
}
else
{
i = len;
h = n - 1;
d2 = (d - 1) / len;
}
while (i--)
{
SCM elt = SCM_SIMPLE_VECTOR_REF (obj, h % len);
h = ((h << 8) + (scm_hasher (elt, n, d2))) % n;
}
return h;
}
else
return 1;
case scm_tcs_cons_imcar:
case scm_tcs_cons_nimcar:
if (d) return (scm_hasher (SCM_CAR (obj), n, d/2)