[project @ 1996-01-08 20:28:12 by partain]

[ghc-hetmet.git] / ghc / runtime / gmp / mpz_gcd.c

diff --git a/ghc/runtime/gmp/mpz_gcd.c b/ghc/runtime/gmp/mpz_gcd.c
new file mode 100644 (file)
index 0000000..090c8c5
--- /dev/null
+++ b/ghc/runtime/gmp/mpz_gcd.c
@@ -0,0 +1,169 @@
+/* mpz_gcd -- Calculate the greatest common divisior of two integers.
+
+Copyright (C) 1991 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 General Public License as published by
+the Free Software Foundation; either version 2, 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 General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with the GNU MP Library; see the file COPYING.  If not, write to
+the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "longlong.h"
+
+#ifndef BERKELEY_MP
+void
+#ifdef __STDC__
+mpz_gcd (MP_INT *w, const MP_INT *u, const MP_INT *v)
+#else
+mpz_gcd (w, u, v)
+     MP_INT *w;
+     const MP_INT *u;
+     const MP_INT *v;
+#endif
+#else /* BERKELEY_MP */
+void
+#ifdef __STDC__
+gcd (const MP_INT *u, const MP_INT *v, MP_INT *w)
+#else
+gcd (u, v, w)
+     const MP_INT *u;
+     const MP_INT *v;
+     MP_INT *w;
+#endif
+#endif /* BERKELEY_MP */
+{
+  mp_size usize, vsize, wsize;
+  mp_ptr up_in, vp_in;
+  mp_ptr up, vp;
+  mp_ptr wp;
+  mp_size i;
+  mp_limb d;
+  int bcnt;
+  mp_size w_bcnt;
+  mp_limb cy_digit;
+
+  usize = ABS (u->size);
+  vsize = ABS (v->size);
+
+  /* GCD(0,v) == v.  */
+  if (usize == 0)
+    {
+      if (w->alloc < vsize)
+       _mpz_realloc (w, vsize);
+
+      w->size = vsize;
+      MPN_COPY (w->d, v->d, vsize);
+      return;
+    }
+
+  /* GCD(0,u) == u.  */
+  if (vsize == 0)
+    {
+      if (w->alloc < usize)
+       _mpz_realloc (w, usize);
+
+      w->size = usize;
+      MPN_COPY (w->d, u->d, usize);
+      return;
+    }
+
+  /* Make U odd by shifting it down as many bit positions as there
+     are zero bits.  Put the result in temporary space.  */
+  up = (mp_ptr) alloca (usize * BYTES_PER_MP_LIMB);
+  up_in = u->d;
+  for (i = 0; (d = up_in[i]) == 0; i++)
+    ;
+  count_leading_zeros (bcnt, d & -d);
+  bcnt = BITS_PER_MP_LIMB - 1 - bcnt;
+  usize = mpn_rshift (up, up_in + i, usize - i, bcnt);
+
+  bcnt += i * BITS_PER_MP_LIMB;
+  w_bcnt = bcnt;
+
+  /* Make V odd by shifting it down as many bit positions as there
+     are zero bits.  Put the result in temporary space.  */
+  vp = (mp_ptr) alloca (vsize * BYTES_PER_MP_LIMB);
+  vp_in = v->d;
+  for (i = 0; (d = vp_in[i]) == 0; i++)
+    ;
+  count_leading_zeros (bcnt, d & -d);
+  bcnt = BITS_PER_MP_LIMB - 1 - bcnt;
+  vsize = mpn_rshift (vp, vp_in + i, vsize - i, bcnt);
+
+  /* W_BCNT is set to the minimum of the number of zero bits in U and V.
+     Thus it represents the number of common 2 factors.  */
+  bcnt += i * BITS_PER_MP_LIMB;
+  if (bcnt < w_bcnt)
+    w_bcnt = bcnt;
+
+  for (;;)
+    {
+      int cmp;
+
+      cmp = usize - vsize != 0 ? usize - vsize : mpn_cmp (up, vp, usize);
+
+      /* If U and V have become equal, we have found the GCD.  */
+      if (cmp == 0)
+       break;
+
+      if (cmp > 0)
+       {
+         /* Replace U by (U - V) >> cnt, with cnt being the least value
+            making U odd again.  */
+
+         usize += mpn_sub (up, up, usize, vp, vsize);
+         for (i = 0; (d = up[i]) == 0; i++)
+           ;
+         count_leading_zeros (bcnt, d & -d);
+         bcnt = BITS_PER_MP_LIMB - 1 - bcnt;
+         usize = mpn_rshift (up, up + i, usize - i, bcnt);
+       }
+      else
+       {
+         /* Replace V by (V - U) >> cnt, with cnt being the least value
+            making V odd again.  */
+
+         vsize += mpn_sub (vp, vp, vsize, up, usize);
+         for (i = 0; (d = vp[i]) == 0; i++)
+           ;
+         count_leading_zeros (bcnt, d & -d);
+         bcnt = BITS_PER_MP_LIMB - 1 - bcnt;
+         vsize = mpn_rshift (vp, vp + i, vsize - i, bcnt);
+       }
+    }
+
+  /* GCD(U_IN, V_IN) now is U * 2**W_BCNT.  */
+
+  wsize = usize + w_bcnt / BITS_PER_MP_LIMB + 1;
+  if (w->alloc < wsize)
+    _mpz_realloc (w, wsize);
+
+  wp = w->d;
+
+  MPN_ZERO (wp, w_bcnt / BITS_PER_MP_LIMB);
+
+  cy_digit = mpn_lshift (wp + w_bcnt / BITS_PER_MP_LIMB, up, usize,
+                         w_bcnt % BITS_PER_MP_LIMB);
+  wsize = usize + w_bcnt / BITS_PER_MP_LIMB;
+  if (cy_digit != 0)
+    {
+      wp[wsize] = cy_digit;
+      wsize++;
+    }
+
+  w->size = wsize;
+
+  alloca (0);
+}