--- /dev/null
+/* mpn_sb_divrem_mn -- Divide natural numbers, producing both remainder and
+ quotient.
+
+ THE FUNCTIONS IN THIS FILE ARE INTERNAL FUNCTIONS WITH MUTABLE
+ INTERFACES. IT IS ONLY SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES.
+ IN FACT, IT IS ALMOST GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A
+ FUTURE GNU MP RELEASE.
+
+
+Copyright (C) 1993, 1994, 1995, 1996, 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"
+#include "longlong.h"
+
+/* Divide num (NP/NSIZE) by den (DP/DSIZE) and write
+ the NSIZE-DSIZE least significant quotient limbs at QP
+ and the DSIZE long remainder at NP. If QEXTRA_LIMBS is
+ non-zero, generate that many fraction bits and append them after the
+ other quotient limbs.
+ Return the most significant limb of the quotient, this is always 0 or 1.
+
+ Preconditions:
+ 0. NSIZE >= DSIZE.
+ 1. The most significant bit of the divisor must be set.
+ 2. QP must either not overlap with the input operands at all, or
+ QP + DSIZE >= NP must hold true. (This means that it's
+ possible to put the quotient in the high part of NUM, right after the
+ remainder in NUM.
+ 3. NSIZE >= DSIZE, even if QEXTRA_LIMBS is non-zero.
+ 4. DSIZE >= 2. */
+
+
+#define PREINVERT_VIABLE \
+ (UDIV_TIME > 2 * UMUL_TIME + 6 /* && ! TARGET_REGISTER_STARVED */)
+
+mp_limb_t
+#if __STDC__
+mpn_sb_divrem_mn (mp_ptr qp,
+ mp_ptr np, mp_size_t nsize,
+ mp_srcptr dp, mp_size_t dsize)
+#else
+mpn_sb_divrem_mn (qp, np, nsize, dp, dsize)
+ mp_ptr qp;
+ mp_ptr np;
+ mp_size_t nsize;
+ mp_srcptr dp;
+ mp_size_t dsize;
+#endif
+{
+ mp_limb_t most_significant_q_limb = 0;
+ mp_size_t i;
+ mp_limb_t dx, d1, n0;
+ mp_limb_t dxinv;
+ int have_preinv;
+
+ ASSERT_ALWAYS (dsize > 2);
+
+ np += nsize - dsize;
+ dx = dp[dsize - 1];
+ d1 = dp[dsize - 2];
+ n0 = np[dsize - 1];
+
+ if (n0 >= dx)
+ {
+ if (n0 > dx || mpn_cmp (np, dp, dsize - 1) >= 0)
+ {
+ mpn_sub_n (np, np, dp, dsize);
+ most_significant_q_limb = 1;
+ }
+ }
+
+ /* If multiplication is much faster than division, preinvert the
+ most significant divisor limb before entering the loop. */
+ if (PREINVERT_VIABLE)
+ {
+ have_preinv = 0;
+ if ((UDIV_TIME - (2 * UMUL_TIME + 6)) * (nsize - dsize) > UDIV_TIME)
+ {
+ invert_limb (dxinv, dx);
+ have_preinv = 1;
+ }
+ }
+
+ for (i = nsize - dsize - 1; i >= 0; i--)
+ {
+ mp_limb_t q;
+ mp_limb_t nx;
+ mp_limb_t cy_limb;
+
+ nx = np[dsize - 1];
+ np--;
+
+ if (nx == dx)
+ {
+ /* This might over-estimate q, but it's probably not worth
+ the extra code here to find out. */
+ q = ~(mp_limb_t) 0;
+
+#if 1
+ cy_limb = mpn_submul_1 (np, dp, dsize, q);
+#else
+ /* This should be faster on many machines */
+ cy_limb = mpn_sub_n (np + 1, np + 1, dp, dsize);
+ cy = mpn_add_n (np, np, dp, dsize);
+ np[dsize] += cy;
+#endif
+
+ if (nx != cy_limb)
+ {
+ mpn_add_n (np, np, dp, dsize);
+ q--;
+ }
+
+ qp[i] = q;
+ }
+ else
+ {
+ mp_limb_t rx, r1, r0, p1, p0;
+
+ /* "workaround" avoids a problem with gcc 2.7.2.3 i386 register
+ usage when np[dsize-1] is used in an asm statement like
+ umul_ppmm in udiv_qrnnd_preinv. The symptom is seg faults due
+ to registers being clobbered. gcc 2.95 i386 doesn't have the
+ problem. */
+ {
+ mp_limb_t workaround = np[dsize - 1];
+ if (PREINVERT_VIABLE && have_preinv)
+ udiv_qrnnd_preinv (q, r1, nx, workaround, dx, dxinv);
+ else
+ udiv_qrnnd (q, r1, nx, workaround, dx);
+ }
+ umul_ppmm (p1, p0, d1, q);
+
+ r0 = np[dsize - 2];
+ rx = 0;
+ if (r1 < p1 || (r1 == p1 && r0 < p0))
+ {
+ p1 -= p0 < d1;
+ p0 -= d1;
+ q--;
+ r1 += dx;
+ rx = r1 < dx;
+ }
+
+ p1 += r0 < p0; /* cannot carry! */
+ rx -= r1 < p1; /* may become 11..1 if q is still too large */
+ r1 -= p1;
+ r0 -= p0;
+
+ cy_limb = mpn_submul_1 (np, dp, dsize - 2, q);
+
+ {
+ mp_limb_t cy1, cy2;
+ cy1 = r0 < cy_limb;
+ r0 -= cy_limb;
+ cy2 = r1 < cy1;
+ r1 -= cy1;
+ np[dsize - 1] = r1;
+ np[dsize - 2] = r0;
+ if (cy2 != rx)
+ {
+ mpn_add_n (np, np, dp, dsize);
+ q--;
+ }
+ }
+ qp[i] = q;
+ }
+ }
+
+ /* ______ ______ ______
+ |__rx__|__r1__|__r0__| partial remainder
+ ______ ______
+ - |__p1__|__p0__| partial product to subtract
+ ______ ______
+ - |______|cylimb|
+
+ rx is -1, 0 or 1. If rx=1, then q is correct (it should match
+ carry out). If rx=-1 then q is too large. If rx=0, then q might
+ be too large, but it is most likely correct.
+ */
+
+ return most_significant_q_limb;
+}
projects / ghc-hetmet.git / blobdiff