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Fix the range of `random' on 64-bit platforms

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For > 32 bit integers still in the fixnum range, scm_random() would
return random numbers with a lower range than specified.

* libguile/random.c (scm_i_mask32): New static inline function.
  (scm_c_random): Use `scm_i_mask32'.
  (scm_c_random64): New function, 64-bit variant of scm_c_random.
  (scm_random): Use `scm_c_random64' instead of forming the 64-bit random
  number in a bogus way.
* libguile/random.h: Added `scm_c_random64'.
This commit is contained in:
Andreas Rottmann 2010-08-01 21:53:29 +02:00 • committed by Andy Wingo
parent 7387c231ee
commit 2af6e1351d
2 changed files with 28 additions and 15 deletions
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42
libguile/random.c
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@ -241,21 +241,42 @@ scm_c_exp1 (scm_t_rstate *state)
unsigned char scm_masktab[256];
scm_t_uint32
scm_c_random (scm_t_rstate *state, scm_t_uint32 m)
static inline scm_t_uint32
scm_i_mask32 (scm_t_uint32 m)
{
scm_t_uint32 r, mask;
mask = (m < 0x100
return (m < 0x100
? scm_masktab[m]
: (m < 0x10000
? scm_masktab[m >> 8] << 8 | 0xff
: (m < 0x1000000
? scm_masktab[m >> 16] << 16 | 0xffff
: scm_masktab[m >> 24] << 24 | 0xffffff)));
}
scm_t_uint32
scm_c_random (scm_t_rstate *state, scm_t_uint32 m)
{
scm_t_uint32 r, mask = scm_i_mask32 (m);
while ((r = state->rng->random_bits (state) & mask) >= m);
return r;
}
scm_t_uint64
scm_c_random64 (scm_t_rstate *state, scm_t_uint64 m)
{
scm_t_uint64 r;
scm_t_uint32 mask;
if (m <= SCM_T_UINT32_MAX)
return scm_c_random (state, (scm_t_uint32) m);
mask = scm_i_mask32 (m >> 32);
while ((r = ((scm_t_uint64) (state->rng->random_bits (state) & mask) << 32)
| state->rng->random_bits (state)) >= m)
;
return r;
}
/*
SCM scm_c_random_bignum (scm_t_rstate *state, SCM m)
@ -377,17 +398,8 @@ SCM_DEFINE (scm_random, "random", 1, 1, 0,
return scm_from_uint32 (scm_c_random (SCM_RSTATE (state),
(scm_t_uint32) m));
#elif SCM_SIZEOF_UNSIGNED_LONG <= 8
if (m <= SCM_T_UINT32_MAX)
return scm_from_uint32 (scm_c_random (SCM_RSTATE (state),
(scm_t_uint32) m));
else
{
scm_t_uint64 upper, lower;
upper = scm_c_random (SCM_RSTATE (state), (scm_t_uint32) (m >> 32));
lower = scm_c_random (SCM_RSTATE (state), SCM_T_UINT32_MAX);
return scm_from_uint64 ((upper << 32) | lower);
}
return scm_from_uint64 (scm_c_random64 (SCM_RSTATE (state),
(scm_t_uint64) m));
#else
#error "Cannot deal with this platform's unsigned long size"
#endif