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Fix random number generator on 64-bit platforms

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* libguile/random.c (scm_c_random): On platforms where `unsigned long' has 64
  bit, generate up to 64 bit of randomness. This is expected by
  scm_c_random_bignum(), and hence was a serious distortion of the random value
  distribution for values exceeding 2^32. This change also fixes a crash when
  the `m' argument is a value above 2^32.
This commit is contained in:
Andreas Rottmann 2010-07-19 22:40:56 +02:00 • committed by Andy Wingo
parent d68a81e038
commit 442eaa681b
1 changed files with 27 additions and 1 deletions
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28
libguile/random.c
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@ -223,7 +223,8 @@ unsigned char scm_masktab[256];
unsigned long
scm_c_random (scm_t_rstate *state, unsigned long m)
{
unsigned int r, mask;
unsigned long r, mask;
#if SCM_SIZEOF_UNSIGNED_LONG == 4
mask = (m < 0x100
? scm_masktab[m]
: (m < 0x10000
@ -232,6 +233,31 @@ scm_c_random (scm_t_rstate *state, unsigned long m)
? scm_masktab[m >> 16] << 16 | 0xffff
: scm_masktab[m >> 24] << 24 | 0xffffff)));
while ((r = scm_the_rng.random_bits (state) & mask) >= m);
#elif SCM_SIZEOF_UNSIGNED_LONG == 8
mask = (m < 0x100
? scm_masktab[m]
: (m < 0x10000
? scm_masktab[m >> 8] << 8 | 0xff
: (m < 0x1000000
? scm_masktab[m >> 16] << 16 | 0xffff
: (m < (1UL << 32)
? scm_masktab[m >> 24] << 24 | 0xffffff
: (m < (1UL << 40)
? ((unsigned long) scm_masktab[m >> 32] << 32
| 0xffffffffUL)
: (m < (1UL << 48)
? ((unsigned long) scm_masktab[m >> 40] << 40
| 0xffffffffffUL)
: (m < (1UL << 56)
? ((unsigned long) scm_masktab[m >> 48] << 48
| 0xffffffffffffUL)
: ((unsigned long) scm_masktab[m >> 56] << 56
| 0xffffffffffffffUL))))))));
while ((r = ((scm_the_rng.random_bits (state) << 32
| scm_the_rng.random_bits (state))) & mask) >= m);
#else
#error "Cannot deal with this platform's unsigned long size"
#endif
return r;
}