1 files changed, 77 insertions, 0 deletions
diff --git a/rts/gmp/mpn/generic/diveby3.c b/rts/gmp/mpn/generic/diveby3.c
new file mode 100644
index 0000000000..a2fb552bfa
--- /dev/null
+++ b/rts/gmp/mpn/generic/diveby3.c
@@ -0,0 +1,77 @@
+/* mpn_divexact_by3 -- mpn division by 3, expecting no remainder. */
+
+/*
+Copyright (C) 2000 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 2.1 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; see the file COPYING.LIB.  If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA.
+*/
+
+
+#include "gmp.h"
+#include "gmp-impl.h"
+
+
+/* Multiplicative inverse of 3, modulo 2^BITS_PER_MP_LIMB.
+   0xAAAAAAAB for 32 bits, 0xAAAAAAAAAAAAAAAB for 64 bits. */
+#define INVERSE_3      ((MP_LIMB_T_MAX / 3) * 2 + 1)
+
+
+/* The "c += ..."s are adding the high limb of 3*l to c.  That high limb
+   will be 0, 1 or 2.  Doing two separate "+="s seems to turn out better
+   code on gcc (as of 2.95.2 at least).
+
+   When a subtraction of a 0,1,2 carry value causes a borrow, that leaves a
+   limb value of either 0xFF...FF or 0xFF...FE and the multiply by INVERSE_3
+   gives 0x55...55 or 0xAA...AA respectively, producing a further borrow of
+   only 0 or 1 respectively.  Hence the carry out of each stage and for the
+   return value is always only 0, 1 or 2.  */
+
+mp_limb_t
+#if __STDC__
+mpn_divexact_by3c (mp_ptr dst, mp_srcptr src, mp_size_t size, mp_limb_t c)
+#else
+mpn_divexact_by3c (dst, src, size, c)
+     mp_ptr    dst;
+     mp_srcptr src;
+     mp_size_t size;
+     mp_limb_t c;
+#endif
+{
+  mp_size_t  i;
+
+  ASSERT (size >= 1);
+
+  i = 0;
+  do
+    {
+      mp_limb_t  l, s;
+
+      s = src[i];
+      l = s - c;
+      c = (l > s);
+
+      l *= INVERSE_3;
+      dst[i] = l;
+
+      c += (l > MP_LIMB_T_MAX/3);
+      c += (l > (MP_LIMB_T_MAX/3)*2);
+    }
+  while (++i < size);
+
+  return c;
+}