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authorAndy Wingo <wingo@pobox.com>2010-07-26 14:34:27 +0200
committerAndy Wingo <wingo@pobox.com>2010-07-26 14:38:20 +0200
commit3bac8ddf92edc1f954b8f3cd3a8f0f89623cfcda (patch)
treeca78ecf14b93d8cd9801b6a621b121bf4d0b8da8
parentdb6e848d195cb2e887f119dd2831483a83b2572b (diff)
downloadguile-3bac8ddf92edc1f954b8f3cd3a8f0f89623cfcda.tar.gz
though scm_c_random returns a ulong, it's only 32 random bits
* libguile/random.c (scm_c_random): Revert previous patch adapting to assume ulong-sized bits, as the RNGs really only give us 32 bits at a time. (scm_c_random_bignum): Adjust to expect random_bits giving us 32 bits at a time. * libguile/random.h: Add comments.
-rw-r--r--libguile/random.c59
-rw-r--r--libguile/random.h5
2 files changed, 21 insertions, 43 deletions
diff --git a/libguile/random.c b/libguile/random.c
index 8785eac2e..e150fb4dc 100644
--- a/libguile/random.c
+++ b/libguile/random.c
@@ -178,11 +178,11 @@ scm_c_exp1 (scm_t_rstate *state)
unsigned char scm_masktab[256];
+/* Returns 32 random bits. */
unsigned long
scm_c_random (scm_t_rstate *state, unsigned long m)
{
- unsigned long r, mask;
-#if SCM_SIZEOF_UNSIGNED_LONG == 4
+ scm_t_uint32 r, mask;
mask = (m < 0x100
? scm_masktab[m]
: (m < 0x10000
@@ -191,31 +191,6 @@ 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;
}
@@ -239,24 +214,24 @@ scm_c_random_bignum (scm_t_rstate *state, SCM m)
{
SCM result = scm_i_mkbig ();
const size_t m_bits = mpz_sizeinbase (SCM_I_BIG_MPZ (m), 2);
- /* how many bits would only partially fill the last unsigned long? */
- const size_t end_bits = m_bits % (sizeof (unsigned long) * SCM_CHAR_BIT);
- unsigned long *random_chunks = NULL;
- const unsigned long num_full_chunks =
- m_bits / (sizeof (unsigned long) * SCM_CHAR_BIT);
- const unsigned long num_chunks = num_full_chunks + ((end_bits) ? 1 : 0);
+ /* how many bits would only partially fill the last u32? */
+ const size_t end_bits = m_bits % (sizeof (scm_t_uint32) * SCM_CHAR_BIT);
+ scm_t_uint32 *random_chunks = NULL;
+ const scm_t_uint32 num_full_chunks =
+ m_bits / (sizeof (scm_t_uint32) * SCM_CHAR_BIT);
+ const scm_t_uint32 num_chunks = num_full_chunks + ((end_bits) ? 1 : 0);
/* we know the result will be this big */
mpz_realloc2 (SCM_I_BIG_MPZ (result), m_bits);
random_chunks =
- (unsigned long *) scm_gc_calloc (num_chunks * sizeof (unsigned long),
+ (scm_t_uint32 *) scm_gc_calloc (num_chunks * sizeof (scm_t_uint32),
"random bignum chunks");
do
{
- unsigned long *current_chunk = random_chunks + (num_chunks - 1);
- unsigned long chunks_left = num_chunks;
+ scm_t_uint32 *current_chunk = random_chunks + (num_chunks - 1);
+ scm_t_uint32 chunks_left = num_chunks;
mpz_set_ui (SCM_I_BIG_MPZ (result), 0);
@@ -265,23 +240,23 @@ scm_c_random_bignum (scm_t_rstate *state, SCM m)
/* generate a mask with ones in the end_bits position, i.e. if
end_bits is 3, then we'd have a mask of ...0000000111 */
const unsigned long rndbits = scm_the_rng.random_bits (state);
- int rshift = (sizeof (unsigned long) * SCM_CHAR_BIT) - end_bits;
- unsigned long mask = ((unsigned long) ULONG_MAX) >> rshift;
- unsigned long highest_bits = rndbits & mask;
+ int rshift = (sizeof (scm_t_uint32) * SCM_CHAR_BIT) - end_bits;
+ scm_t_uint32 mask = 0xffffffff >> rshift;
+ scm_t_uint32 highest_bits = ((scm_t_uint32) rndbits) & mask;
*current_chunk-- = highest_bits;
chunks_left--;
}
while (chunks_left)
{
- /* now fill in the remaining unsigned long sized chunks */
+ /* now fill in the remaining scm_t_uint32 sized chunks */
*current_chunk-- = scm_the_rng.random_bits (state);
chunks_left--;
}
mpz_import (SCM_I_BIG_MPZ (result),
num_chunks,
-1,
- sizeof (unsigned long),
+ sizeof (scm_t_uint32),
0,
0,
random_chunks);
@@ -289,7 +264,7 @@ scm_c_random_bignum (scm_t_rstate *state, SCM m)
all bits in order not to get a distorted distribution) */
} while (mpz_cmp (SCM_I_BIG_MPZ (result), SCM_I_BIG_MPZ (m)) >= 0);
scm_gc_free (random_chunks,
- num_chunks * sizeof (unsigned long),
+ num_chunks * sizeof (scm_t_uint32),
"random bignum chunks");
return scm_i_normbig (result);
}
diff --git a/libguile/random.h b/libguile/random.h
index 6ec43ff53..c16fa0efb 100644
--- a/libguile/random.h
+++ b/libguile/random.h
@@ -3,7 +3,7 @@
#ifndef SCM_RANDOM_H
#define SCM_RANDOM_H
-/* Copyright (C) 1999,2000,2001, 2006 Free Software Foundation, Inc.
+/* Copyright (C) 1999,2000,2001, 2006, 2010 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
@@ -45,6 +45,7 @@ typedef struct scm_t_rstate {
typedef struct scm_t_rng {
size_t rstate_size; /* size of random state */
+ /* Though this returns an unsigned long, it's only 32 bits of randomness. */
unsigned long (*random_bits) (scm_t_rstate *state); /* gives 32 random bits */
void (*init_rstate) (scm_t_rstate *state, const char *seed, int n);
scm_t_rstate *(*copy_rstate) (scm_t_rstate *state);
@@ -62,6 +63,7 @@ typedef struct scm_t_i_rstate {
unsigned long c;
} scm_t_i_rstate;
+/* Though this returns an unsigned long, it's only 32 bits of randomness. */
SCM_API unsigned long scm_i_uniform32 (scm_t_i_rstate *);
SCM_API void scm_i_init_rstate (scm_t_i_rstate *, const char *seed, int n);
SCM_API scm_t_i_rstate *scm_i_copy_rstate (scm_t_i_rstate *);
@@ -76,6 +78,7 @@ SCM_API scm_t_rstate *scm_c_default_rstate (void);
SCM_API double scm_c_uniform01 (scm_t_rstate *);
SCM_API double scm_c_normal01 (scm_t_rstate *);
SCM_API double scm_c_exp1 (scm_t_rstate *);
+/* Though this returns an unsigned long, it's only 32 bits of randomness. */
SCM_API unsigned long scm_c_random (scm_t_rstate *, unsigned long m);
SCM_API SCM scm_c_random_bignum (scm_t_rstate *, SCM m);