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

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

diff --git a/ghc/runtime/gmp/mpq_sub.c b/ghc/runtime/gmp/mpq_sub.c
new file mode 100644 (file)
index 0000000..a512705
--- /dev/null
+++ b/ghc/runtime/gmp/mpq_sub.c
@@ -0,0 +1,85 @@
+/* mpq_sub -- subtract two rational numbers.
+
+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"
+
+void
+#ifdef __STDC__
+mpq_sub (MP_RAT *dif, const MP_RAT *min, const MP_RAT *sub)
+#else
+mpq_sub (dif, min, sub)
+     MP_RAT *dif;
+     const MP_RAT *min;
+     const MP_RAT *sub;
+#endif
+{
+  MP_INT gcd1, gcd2;
+  MP_INT tmp1, tmp2;
+
+  mpz_init (&gcd1);
+  mpz_init (&gcd2);
+  mpz_init (&tmp1);
+  mpz_init (&tmp2);
+
+  /* DIF might be identical to either operand, so don't store the
+     result there until we are finished with the input operands.  We
+     dare to overwrite the numerator of DIF when we are finished
+     with the numerators of MIN and SUB.  */
+
+  mpz_gcd (&gcd1, &(min->den), &(sub->den));
+  if (gcd1.size > 1 || gcd1.d[0] != 1)
+    {
+      MP_INT t;
+
+      mpz_init (&t);
+
+      mpz_div (&tmp1, &(sub->den), &gcd1);
+      mpz_mul (&tmp1, &(min->num), &tmp1);
+
+      mpz_div (&tmp2, &(min->den), &gcd1);
+      mpz_mul (&tmp2, &(sub->num), &tmp2);
+
+      mpz_sub (&t, &tmp1, &tmp2);
+      mpz_gcd (&gcd2, &t, &gcd1);
+
+      mpz_div (&(dif->num), &t, &gcd2);
+
+      mpz_div (&tmp1, &(min->den), &gcd1);
+      mpz_div (&tmp2, &(sub->den), &gcd2);
+      mpz_mul (&(dif->den), &tmp1, &tmp2);
+
+      mpz_clear (&t);
+    }
+  else
+    {
+      /* The common divisior is 1.  This is the case (for random input) with
+        probability 6/(pi**2).  */
+      mpz_mul (&tmp1, &(min->num), &(sub->den));
+      mpz_mul (&tmp2, &(sub->num), &(min->den));
+      mpz_sub (&(dif->num), &tmp1, &tmp2);
+      mpz_mul (&(dif->den), &(min->den), &(sub->den));
+    }
+
+  mpz_clear (&tmp2);
+  mpz_clear (&tmp1);
+  mpz_clear (&gcd2);
+  mpz_clear (&gcd1);
+}