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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.
This commit is contained in:
Andy Wingo
parent
db6e848d19
commit
3bac8ddf92
2 changed files with 21 additions and 43 deletions
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@ -178,11 +178,11 @@ scm_c_exp1 (scm_t_rstate *state)
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unsigned char scm_masktab[256];
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/* Returns 32 random bits. */
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unsigned long
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scm_c_random (scm_t_rstate *state, unsigned long m)
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{
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unsigned long r, mask;
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#if SCM_SIZEOF_UNSIGNED_LONG == 4
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scm_t_uint32 r, mask;
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mask = (m < 0x100
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? scm_masktab[m]
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: (m < 0x10000
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@ -191,31 +191,6 @@ scm_c_random (scm_t_rstate *state, unsigned long m)
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? scm_masktab[m >> 16] << 16 | 0xffff
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: scm_masktab[m >> 24] << 24 | 0xffffff)));
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while ((r = scm_the_rng.random_bits (state) & mask) >= m);
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#elif SCM_SIZEOF_UNSIGNED_LONG == 8
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mask = (m < 0x100
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? scm_masktab[m]
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: (m < 0x10000
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? scm_masktab[m >> 8] << 8 | 0xff
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: (m < 0x1000000
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? scm_masktab[m >> 16] << 16 | 0xffff
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: (m < (1UL << 32)
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? scm_masktab[m >> 24] << 24 | 0xffffff
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: (m < (1UL << 40)
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? ((unsigned long) scm_masktab[m >> 32] << 32
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| 0xffffffffUL)
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: (m < (1UL << 48)
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? ((unsigned long) scm_masktab[m >> 40] << 40
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| 0xffffffffffUL)
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: (m < (1UL << 56)
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? ((unsigned long) scm_masktab[m >> 48] << 48
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| 0xffffffffffffUL)
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: ((unsigned long) scm_masktab[m >> 56] << 56
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| 0xffffffffffffffUL))))))));
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while ((r = ((scm_the_rng.random_bits (state) << 32
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| scm_the_rng.random_bits (state))) & mask) >= m);
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#else
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#error "Cannot deal with this platform's unsigned long size"
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#endif
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return r;
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}
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@ -239,24 +214,24 @@ scm_c_random_bignum (scm_t_rstate *state, SCM m)
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{
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SCM result = scm_i_mkbig ();
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const size_t m_bits = mpz_sizeinbase (SCM_I_BIG_MPZ (m), 2);
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/* how many bits would only partially fill the last unsigned long? */
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const size_t end_bits = m_bits % (sizeof (unsigned long) * SCM_CHAR_BIT);
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unsigned long *random_chunks = NULL;
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const unsigned long num_full_chunks =
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m_bits / (sizeof (unsigned long) * SCM_CHAR_BIT);
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const unsigned long num_chunks = num_full_chunks + ((end_bits) ? 1 : 0);
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/* how many bits would only partially fill the last u32? */
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const size_t end_bits = m_bits % (sizeof (scm_t_uint32) * SCM_CHAR_BIT);
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scm_t_uint32 *random_chunks = NULL;
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const scm_t_uint32 num_full_chunks =
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m_bits / (sizeof (scm_t_uint32) * SCM_CHAR_BIT);
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const scm_t_uint32 num_chunks = num_full_chunks + ((end_bits) ? 1 : 0);
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/* we know the result will be this big */
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mpz_realloc2 (SCM_I_BIG_MPZ (result), m_bits);
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random_chunks =
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(unsigned long *) scm_gc_calloc (num_chunks * sizeof (unsigned long),
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(scm_t_uint32 *) scm_gc_calloc (num_chunks * sizeof (scm_t_uint32),
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"random bignum chunks");
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do
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{
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unsigned long *current_chunk = random_chunks + (num_chunks - 1);
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unsigned long chunks_left = num_chunks;
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scm_t_uint32 *current_chunk = random_chunks + (num_chunks - 1);
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scm_t_uint32 chunks_left = num_chunks;
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mpz_set_ui (SCM_I_BIG_MPZ (result), 0);
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@ -265,23 +240,23 @@ scm_c_random_bignum (scm_t_rstate *state, SCM m)
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/* generate a mask with ones in the end_bits position, i.e. if
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end_bits is 3, then we'd have a mask of ...0000000111 */
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const unsigned long rndbits = scm_the_rng.random_bits (state);
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int rshift = (sizeof (unsigned long) * SCM_CHAR_BIT) - end_bits;
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unsigned long mask = ((unsigned long) ULONG_MAX) >> rshift;
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unsigned long highest_bits = rndbits & mask;
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int rshift = (sizeof (scm_t_uint32) * SCM_CHAR_BIT) - end_bits;
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scm_t_uint32 mask = 0xffffffff >> rshift;
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scm_t_uint32 highest_bits = ((scm_t_uint32) rndbits) & mask;
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*current_chunk-- = highest_bits;
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chunks_left--;
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}
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while (chunks_left)
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{
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/* now fill in the remaining unsigned long sized chunks */
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/* now fill in the remaining scm_t_uint32 sized chunks */
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*current_chunk-- = scm_the_rng.random_bits (state);
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chunks_left--;
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}
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mpz_import (SCM_I_BIG_MPZ (result),
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num_chunks,
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-1,
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sizeof (unsigned long),
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sizeof (scm_t_uint32),
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0,
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0,
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random_chunks);
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@ -289,7 +264,7 @@ scm_c_random_bignum (scm_t_rstate *state, SCM m)
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all bits in order not to get a distorted distribution) */
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} while (mpz_cmp (SCM_I_BIG_MPZ (result), SCM_I_BIG_MPZ (m)) >= 0);
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scm_gc_free (random_chunks,
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num_chunks * sizeof (unsigned long),
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num_chunks * sizeof (scm_t_uint32),
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"random bignum chunks");
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return scm_i_normbig (result);
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}
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@ -3,7 +3,7 @@
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#ifndef SCM_RANDOM_H
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#define SCM_RANDOM_H
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/* Copyright (C) 1999,2000,2001, 2006 Free Software Foundation, Inc.
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/* Copyright (C) 1999,2000,2001, 2006, 2010 Free Software Foundation, Inc.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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@ -45,6 +45,7 @@ typedef struct scm_t_rstate {
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typedef struct scm_t_rng {
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size_t rstate_size; /* size of random state */
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/* Though this returns an unsigned long, it's only 32 bits of randomness. */
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unsigned long (*random_bits) (scm_t_rstate *state); /* gives 32 random bits */
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void (*init_rstate) (scm_t_rstate *state, const char *seed, int n);
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scm_t_rstate *(*copy_rstate) (scm_t_rstate *state);
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@ -62,6 +63,7 @@ typedef struct scm_t_i_rstate {
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unsigned long c;
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} scm_t_i_rstate;
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/* Though this returns an unsigned long, it's only 32 bits of randomness. */
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SCM_API unsigned long scm_i_uniform32 (scm_t_i_rstate *);
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SCM_API void scm_i_init_rstate (scm_t_i_rstate *, const char *seed, int n);
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SCM_API scm_t_i_rstate *scm_i_copy_rstate (scm_t_i_rstate *);
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@ -76,6 +78,7 @@ SCM_API scm_t_rstate *scm_c_default_rstate (void);
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SCM_API double scm_c_uniform01 (scm_t_rstate *);
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SCM_API double scm_c_normal01 (scm_t_rstate *);
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SCM_API double scm_c_exp1 (scm_t_rstate *);
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/* Though this returns an unsigned long, it's only 32 bits of randomness. */
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SCM_API unsigned long scm_c_random (scm_t_rstate *, unsigned long m);
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SCM_API SCM scm_c_random_bignum (scm_t_rstate *, SCM m);
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