[Guile-commits] GNU Guile branch, branch_release-1-8, updated. release_1-8-7-23-g33290f5

[Andy Wingo]

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http://git.savannah.gnu.org/cgit/guile.git/commit/?id=33290f52ef171050b0d692ba3caf7ab15b30b84f

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- Log -----------------------------------------------------------------
commit 33290f52ef171050b0d692ba3caf7ab15b30b84f
Author: Andreas Rottmann <address@hidden>
Date:   Mon Jul 19 22:55:16 2010 +0200

    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.

-----------------------------------------------------------------------

Summary of changes:
 libguile/random.c |   28 +++++++++++++++++++++++++++-
 1 files changed, 27 insertions(+), 1 deletions(-)

diff --git a/libguile/random.c b/libguile/random.c
index 8d2ff03..3c2d2aa 100644
--- a/libguile/random.c
+++ b/libguile/random.c
@@ -215,7 +215,8 @@ 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
@@ -224,6 +225,31 @@ 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;
 }
 


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