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author | Torbjorn Granlund <tege@gmplib.org> | 2010-11-11 09:56:42 +0100 |
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committer | Torbjorn Granlund <tege@gmplib.org> | 2010-11-11 09:56:42 +0100 |
commit | fb80223734ba92b2a182f29b00751e509dbece06 (patch) | |
tree | 014931d1dc5a4f1024644986a489c3859f1df727 /rand/randmui.c | |
parent | 5b824f09ff34399acf7458217a903c928f7eb83b (diff) | |
download | gmp-fb80223734ba92b2a182f29b00751e509dbece06.tar.gz |
Move global random file to new 'rand' subdirectory.
Diffstat (limited to 'rand/randmui.c')
-rw-r--r-- | rand/randmui.c | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/rand/randmui.c b/rand/randmui.c new file mode 100644 index 000000000..f349d3593 --- /dev/null +++ b/rand/randmui.c @@ -0,0 +1,75 @@ +/* gmp_urandomm_ui -- uniform random number 0 to N-1 for ulong N. + +Copyright 2003, 2004 Free Software Foundation, Inc. + +This file is part of the GNU MP Library. + +The GNU MP Library is free software; you can redistribute it and/or modify +it under the terms of the GNU Lesser General Public License as published by +the Free Software Foundation; either version 3 of the License, or (at your +option) any later version. + +The GNU MP Library is distributed in the hope that it will be useful, but +WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY +or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public +License for more details. + +You should have received a copy of the GNU Lesser General Public License +along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ + +#include "gmp.h" +#include "gmp-impl.h" +#include "longlong.h" + + +/* If n is a power of 2 then the test ret<n is always true and the loop is + unnecessary, but there's no need to add special code for this. Just get + the "bits" calculation correct and let it go through normally. + + If n is 1 then will have bits==0 and _gmp_rand will produce no output and + we always return 0. Again there seems no need for a special case, just + initialize a[0]=0 and let it go through normally. */ + +#define MAX_URANDOMM_ITER 80 + +unsigned long +gmp_urandomm_ui (gmp_randstate_ptr rstate, unsigned long n) +{ + mp_limb_t a[LIMBS_PER_ULONG]; + unsigned long ret, bits, leading; + int i; + + if (UNLIKELY (n == 0)) + DIVIDE_BY_ZERO; + + /* start with zeros, since if bits==0 then _gmp_rand will store nothing at + all (bits==0 arises when n==1), or if bits <= GMP_NUMB_BITS then it + will store only a[0]. */ + a[0] = 0; +#if LIMBS_PER_ULONG > 1 + a[1] = 0; +#endif + + count_leading_zeros (leading, (mp_limb_t) n); + bits = GMP_LIMB_BITS - leading - (POW2_P(n) != 0); + + for (i = 0; i < MAX_URANDOMM_ITER; i++) + { + _gmp_rand (a, rstate, bits); +#if LIMBS_PER_ULONG == 1 + ret = a[0]; +#else + ret = a[0] | (a[1] << GMP_NUMB_BITS); +#endif + if (LIKELY (ret < n)) /* usually one iteration suffices */ + goto done; + } + + /* Too many iterations, there must be something degenerate about the + rstate algorithm. Return r%n. */ + ret -= n; + ASSERT (ret < n); + + done: + return ret; +} |