--- /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 1993, 1994, 1995, 1996, 2000, 2001, 2002 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"
+
+
+/* The size where udiv_qrnnd_preinv should be used rather than udiv_qrnnd,
+ meaning the quotient size where that should happen, the quotient size
+ being how many udiv divisions will be done.
+
+ The default is to use preinv always, CPUs where this doesn't suit have
+ tuned thresholds. Note in particular that preinv should certainly be
+ used if that's the only division available (USE_PREINV_ALWAYS). */
+
+#ifndef DIV_SB_PREINV_THRESHOLD
+#define DIV_SB_PREINV_THRESHOLD 0
+#endif
+
+
+/* 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.
+ 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.
+ 4. DSIZE > 2. */
+
+
+mp_limb_t
+mpn_sb_divrem_mn (mp_ptr qp,
+ mp_ptr np, mp_size_t nn,
+ mp_srcptr dp, mp_size_t dn)
+{
+ mp_limb_t most_significant_q_limb = 0;
+ mp_size_t qn = nn - dn;
+ mp_size_t i;
+ mp_limb_t dx, d1, n0;
+ mp_limb_t dxinv;
+ int use_preinv;
+
+ ASSERT (dn > 2);
+ ASSERT (nn >= dn);
+ ASSERT (dp[dn-1] & GMP_NUMB_HIGHBIT);
+ ASSERT (! MPN_OVERLAP_P (np, nn, dp, dn));
+ ASSERT (! MPN_OVERLAP_P (qp, nn-dn, dp, dn));
+ ASSERT (! MPN_OVERLAP_P (qp, nn-dn, np, nn) || qp+dn >= np);
+ ASSERT_MPN (np, nn);
+ ASSERT_MPN (dp, dn);
+
+ np += qn;
+ dx = dp[dn - 1];
+ d1 = dp[dn - 2];
+ n0 = np[dn - 1];
+
+ if (n0 >= dx)
+ {
+ if (n0 > dx || mpn_cmp (np, dp, dn - 1) >= 0)
+ {
+ mpn_sub_n (np, np, dp, dn);
+ most_significant_q_limb = 1;
+ }
+ }
+
+ use_preinv = ABOVE_THRESHOLD (qn, DIV_SB_PREINV_THRESHOLD);
+ if (use_preinv)
+ invert_limb (dxinv, dx);
+
+ for (i = qn - 1; i >= 0; i--)
+ {
+ mp_limb_t q;
+ mp_limb_t nx;
+ mp_limb_t cy_limb;
+
+ nx = np[dn - 1]; /* FIXME: could get value from r1 */
+ np--;
+
+ if (nx == dx)
+ {
+ /* This might over-estimate q, but it's probably not worth
+ the extra code here to find out. */
+ q = GMP_NUMB_MASK;
+
+#if 1
+ cy_limb = mpn_submul_1 (np, dp, dn, q);
+#else
+ /* This should be faster on many machines */
+ cy_limb = mpn_sub_n (np + 1, np + 1, dp, dn);
+ cy = mpn_add_n (np, np, dp, dn);
+ np[dn] += cy;
+#endif
+
+ if (nx != cy_limb)
+ {
+ mpn_add_n (np, np, dp, dn);
+ 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[dn-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[dn - 1];
+ if (CACHED_ABOVE_THRESHOLD (use_preinv, DIV_SB_PREINV_THRESHOLD))
+ udiv_qrnnd_preinv (q, r1, nx, workaround, dx, dxinv);
+ else
+ {
+ udiv_qrnnd (q, r1, nx, workaround << GMP_NAIL_BITS,
+ dx << GMP_NAIL_BITS);
+ r1 >>= GMP_NAIL_BITS;
+ }
+ }
+ umul_ppmm (p1, p0, d1, q << GMP_NAIL_BITS);
+ p0 >>= GMP_NAIL_BITS;
+
+ r0 = np[dn - 2];
+ rx = 0;
+ if (r1 < p1 || (r1 == p1 && r0 < p0))
+ {
+ p1 -= p0 < d1;
+ p0 = (p0 - d1) & GMP_NUMB_MASK;
+ q--;
+ r1 = (r1 + dx) & GMP_NUMB_MASK;
+ rx = r1 < dx;
+ }
+
+ p1 += r0 < p0; /* cannot carry! */
+ rx -= r1 < p1; /* may become 11..1 if q is still too large */
+ r1 = (r1 - p1) & GMP_NUMB_MASK;
+ r0 = (r0 - p0) & GMP_NUMB_MASK;
+
+ cy_limb = mpn_submul_1 (np, dp, dn - 2, q);
+
+ /* Check if we've over-estimated q, and adjust as needed. */
+ {
+ mp_limb_t cy1, cy2;
+ cy1 = r0 < cy_limb;
+ r0 = (r0 - cy_limb) & GMP_NUMB_MASK;
+ cy2 = r1 < cy1;
+ r1 -= cy1;
+ np[dn - 1] = r1;
+ np[dn - 2] = r0;
+ if (cy2 != rx)
+ {
+ mpn_add_n (np, np, dp, dn);
+ 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 / msp430-gcc.git / blobdiff