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authorAndreas Rottmann <a.rottmann@gmx.at>2010-07-19 22:40:56 +0200
committerAndy Wingo <wingo@pobox.com>2010-07-19 22:40:56 +0200
commit442eaa681b0c2db4254d4903f8a0996b4ffc83d0 (patch)
treed28496035ffbc5e179218cad7a82f7783be00459 /libguile/random.c
parentd68a81e038597ba3d47f39b4cd8a5864953dc1d5 (diff)
downloadguile-442eaa681b0c2db4254d4903f8a0996b4ffc83d0.tar.gz
Fix random number generator on 64-bit platforms
* 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.
Diffstat (limited to 'libguile/random.c')
-rw-r--r--libguile/random.c28
1 files changed, 27 insertions, 1 deletions
diff --git a/libguile/random.c b/libguile/random.c
index 281d43aa8..1a9fd59ac 100644
--- a/libguile/random.c
+++ b/libguile/random.c
@@ -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;
}