Imported gcc-4.4.3

[msp430-gcc.git] / gmp / randmts.c

diff --git a/gmp/randmts.c b/gmp/randmts.c
new file mode 100644 (file)
index 0000000..e3b0338
--- /dev/null
+++ b/gmp/randmts.c
@@ -0,0 +1,157 @@
+/* Mersenne Twister pseudo-random number generator functions.
+
+Copyright 2002, 2003 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 "randmt.h"
+
+
+/* Calculate (b^e) mod (2^n-k) for e=1074888996, n=19937 and k=20023,
+   needed by the seeding function below.  */
+static void
+mangle_seed (mpz_ptr r, mpz_srcptr b_orig)
+{
+  mpz_t          t, b;
+  unsigned long  e = 0x40118124;
+  unsigned long  bit = 0x20000000;
+
+  mpz_init (t);
+  mpz_init_set (b, b_orig);  /* in case r==b_orig */
+
+  mpz_set (r, b);
+  do
+    {
+      mpz_mul (r, r, r);
+
+    reduce:
+      for (;;)
+        {
+          mpz_tdiv_q_2exp (t, r, 19937L);
+          if (mpz_sgn (t) == 0)
+            break;
+          mpz_tdiv_r_2exp (r, r, 19937L);
+          mpz_addmul_ui (r, t, 20023L);
+        }
+
+      if ((e & bit) != 0)
+        {
+          e &= ~bit;
+          mpz_mul (r, r, b);
+          goto reduce;
+        }
+
+      bit >>= 1;
+    }
+  while (bit != 0);
+
+  mpz_clear (t);
+  mpz_clear (b);
+}
+
+
+/* Seeding function.  Uses powering modulo a non-Mersenne prime to obtain
+   a permutation of the input seed space.  The modulus is 2^19937-20023,
+   which is probably prime.  The power is 1074888996.  In order to avoid
+   seeds 0 and 1 generating invalid or strange output, the input seed is
+   first manipulated as follows:
+
+     seed1 = seed mod (2^19937-20027) + 2
+
+   so that seed1 lies between 2 and 2^19937-20026 inclusive. Then the
+   powering is performed as follows:
+
+     seed2 = (seed1^1074888996) mod (2^19937-20023)
+
+   and then seed2 is used to bootstrap the buffer.
+
+   This method aims to give guarantees that:
+     a) seed2 will never be zero,
+     b) seed2 will very seldom have a very low population of ones in its
+       binary representation, and
+     c) every seed between 0 and 2^19937-20028 (inclusive) will yield a
+       different sequence.
+
+   CAVEATS:
+
+   The period of the seeding function is 2^19937-20027.  This means that
+   with seeds 2^19937-20027, 2^19937-20026, ... the exact same sequences
+   are obtained as with seeds 0, 1, etc.; it also means that seed -1
+   produces the same sequence as seed 2^19937-20028, etc.
+ */
+
+static void
+randseed_mt (gmp_randstate_t rstate, mpz_srcptr seed)
+{
+  int i;
+  size_t cnt;
+
+  gmp_rand_mt_struct *p;
+  mpz_t mod;    /* Modulus.  */
+  mpz_t seed1;  /* Intermediate result.  */
+
+  p = (gmp_rand_mt_struct *) RNG_STATE (rstate);
+
+  mpz_init (mod);
+  mpz_init (seed1);
+
+  mpz_set_ui (mod, 0L);
+  mpz_setbit (mod, 19937L);
+  mpz_sub_ui (mod, mod, 20027L);
+  mpz_mod (seed1, seed, mod);  /* Reduce `seed' modulo `mod'.  */
+  mpz_add_ui (seed1, seed1, 2L);       /* seed1 is now ready.  */
+  mangle_seed (seed1, seed1);  /* Perform the mangling by powering.  */
+
+  /* Copy the last bit into bit 31 of mt[0] and clear it.  */
+  p->mt[0] = (mpz_tstbit (seed1, 19936L) != 0) ? 0x80000000 : 0;
+  mpz_clrbit (seed1, 19936L);
+
+  /* Split seed1 into N-1 32-bit chunks.  */
+  mpz_export (&p->mt[1], &cnt, -1, sizeof (p->mt[1]), 0,
+              8 * sizeof (p->mt[1]) - 32, seed1);
+  cnt++;
+  ASSERT (cnt <= N);
+  while (cnt < N)
+    p->mt[cnt++] = 0;
+
+  mpz_clear (mod);
+  mpz_clear (seed1);
+
+  /* Warm the generator up if necessary.  */
+  if (WARM_UP != 0)
+    for (i = 0; i < WARM_UP / N; i++)
+      __gmp_mt_recalc_buffer (p->mt);
+
+  p->mti = WARM_UP % N;
+}
+
+
+static const gmp_randfnptr_t Mersenne_Twister_Generator = {
+  randseed_mt,
+  __gmp_randget_mt,
+  __gmp_randclear_mt,
+  __gmp_randiset_mt
+};
+
+/* Initialize MT-specific data.  */
+void
+gmp_randinit_mt (gmp_randstate_t rstate)
+{
+  __gmp_randinit_mt_noseed (rstate);
+  RNG_FNPTR (rstate) = (void *) &Mersenne_Twister_Generator;
+}