--- /dev/null
+/* mpn_divexact_1 -- mpn by limb exact division.
+
+ THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE ONLY. THEY'RE ALMOST
+ CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR COMPLETELY IN
+ FUTURE GNU MP RELEASES.
+
+Copyright 2000, 2001, 2002, 2003, 2005 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"
+
+
+
+/* Divide a={src,size} by d=divisor and store the quotient in q={dst,size}.
+ q will only be correct if d divides a exactly.
+
+ A separate loop is used for shift==0 because n<<BITS_PER_MP_LIMB doesn't
+ give zero on all CPUs (for instance it doesn't on the x86s). This
+ separate loop might run faster too, helping odd divisors.
+
+ Possibilities:
+
+ mpn_divexact_1c could be created, accepting and returning c. This would
+ let a long calculation be done piece by piece. Currently there's no
+ particular need for that, and not returning c means that a final umul can
+ be skipped.
+
+ Another use for returning c would be letting the caller know whether the
+ division was in fact exact. It would work just to return the carry bit
+ "c=(l>s)" and let the caller do a final umul if interested.
+
+ When the divisor is even, the factors of two could be handled with a
+ separate mpn_rshift, instead of shifting on the fly. That might be
+ faster on some CPUs and would mean just the shift==0 style loop would be
+ needed.
+
+ If n<<BITS_PER_MP_LIMB gives zero on a particular CPU then the separate
+ shift==0 loop is unnecessary, and could be eliminated if there's no great
+ speed difference.
+
+ It's not clear whether "/" is the best way to handle size==1. Alpha gcc
+ 2.95 for instance has a poor "/" and might prefer the modular method.
+ Perhaps a tuned parameter should control this.
+
+ If src[size-1] < divisor then dst[size-1] will be zero, and one divide
+ step could be skipped. A test at last step for s<divisor (or ls in the
+ even case) might be a good way to do that. But if this code is often
+ used with small divisors then it might not be worth bothering */
+
+void
+mpn_divexact_1 (mp_ptr dst, mp_srcptr src, mp_size_t size, mp_limb_t divisor)
+{
+ mp_size_t i;
+ mp_limb_t c, h, l, ls, s, s_next, inverse, dummy;
+ unsigned shift;
+
+ ASSERT (size >= 1);
+ ASSERT (divisor != 0);
+ ASSERT (MPN_SAME_OR_SEPARATE_P (dst, src, size));
+ ASSERT_MPN (src, size);
+ ASSERT_LIMB (divisor);
+
+ s = src[0];
+
+ if (size == 1)
+ {
+ dst[0] = s / divisor;
+ return;
+ }
+
+ if ((divisor & 1) == 0)
+ {
+ count_trailing_zeros (shift, divisor);
+ divisor >>= shift;
+ }
+ else
+ shift = 0;
+
+ binvert_limb (inverse, divisor);
+ divisor <<= GMP_NAIL_BITS;
+
+ if (shift != 0)
+ {
+ c = 0;
+ i = 0;
+ size--;
+
+ do
+ {
+ s_next = src[i+1];
+ ls = ((s >> shift) | (s_next << (GMP_NUMB_BITS-shift))) & GMP_NUMB_MASK;
+ s = s_next;
+
+ SUBC_LIMB (c, l, ls, c);
+
+ l = (l * inverse) & GMP_NUMB_MASK;
+ dst[i] = l;
+
+ umul_ppmm (h, dummy, l, divisor);
+ c += h;
+
+ i++;
+ }
+ while (i < size);
+
+ ls = s >> shift;
+ l = ls - c;
+ l = (l * inverse) & GMP_NUMB_MASK;
+ dst[i] = l;
+ }
+ else
+ {
+ l = (s * inverse) & GMP_NUMB_MASK;
+ dst[0] = l;
+ i = 1;
+ c = 0;
+
+ do
+ {
+ umul_ppmm (h, dummy, l, divisor);
+ c += h;
+
+ s = src[i];
+ SUBC_LIMB (c, l, s, c);
+
+ l = (l * inverse) & GMP_NUMB_MASK;
+ dst[i] = l;
+ i++;
+ }
+ while (i < size);
+ }
+}
projects / msp430-gcc.git / blobdiff