329 lines
7.6 KiB
C
329 lines
7.6 KiB
C
/* mpf_ui_sub -- Subtract a float from an unsigned long int.
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Copyright 1993, 1994, 1995, 1996, 2001, 2002, 2005 Free Software Foundation,
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Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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#include "mpir.h"
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#include "gmp-impl.h"
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void
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mpf_ui_sub (mpf_ptr r, gmp_ui u, mpf_srcptr v)
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{
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mp_srcptr up, vp;
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mp_ptr rp, tp;
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mp_size_t usize, vsize, rsize;
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mp_size_t prec;
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mp_exp_t uexp;
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mp_size_t ediff;
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int negate;
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mp_limb_t ulimb;
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TMP_DECL;
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vsize = v->_mp_size;
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/* Handle special cases that don't work in generic code below. */
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if (u == 0)
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{
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mpf_neg (r, v);
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return;
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}
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if (vsize == 0)
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{
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mpf_set_ui (r, u);
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return;
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}
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/* If signs of U and V are different, perform addition. */
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if (vsize < 0)
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{
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__mpf_struct v_negated;
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v_negated._mp_size = -vsize;
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v_negated._mp_exp = v->_mp_exp;
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v_negated._mp_d = v->_mp_d;
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mpf_add_ui (r, &v_negated, u);
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return;
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}
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TMP_MARK;
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/* Signs are now known to be the same. */
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ulimb = u;
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/* Make U be the operand with the largest exponent. */
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if (1 < v->_mp_exp)
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{
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negate = 1;
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usize = ABS (vsize);
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vsize = 1;
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up = v->_mp_d;
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vp = &ulimb;
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rp = r->_mp_d;
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prec = r->_mp_prec + 1;
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uexp = v->_mp_exp;
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ediff = uexp - 1;
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}
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else
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{
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negate = 0;
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usize = 1;
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vsize = ABS (vsize);
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up = &ulimb;
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vp = v->_mp_d;
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rp = r->_mp_d;
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prec = r->_mp_prec;
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uexp = 1;
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ediff = 1 - v->_mp_exp;
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}
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/* Ignore leading limbs in U and V that are equal. Doing
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this helps increase the precision of the result. */
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if (ediff == 0)
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{
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/* This loop normally exits immediately. Optimize for that. */
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for (;;)
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{
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usize--;
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vsize--;
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if (up[usize] != vp[vsize])
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break;
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uexp--;
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if (usize == 0)
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goto Lu0;
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if (vsize == 0)
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goto Lv0;
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}
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usize++;
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vsize++;
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/* Note that either operand (but not both operands) might now have
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leading zero limbs. It matters only that U is unnormalized if
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vsize is now zero, and vice versa. And it is only in that case
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that we have to adjust uexp. */
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if (vsize == 0)
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Lv0:
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while (usize != 0 && up[usize - 1] == 0)
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usize--, uexp--;
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if (usize == 0)
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Lu0:
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while (vsize != 0 && vp[vsize - 1] == 0)
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vsize--, uexp--;
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}
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/* If U extends beyond PREC, ignore the part that does. */
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if (usize > prec)
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{
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up += usize - prec;
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usize = prec;
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}
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/* If V extends beyond PREC, ignore the part that does.
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Note that this may make vsize negative. */
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if (vsize + ediff > prec)
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{
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vp += vsize + ediff - prec;
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vsize = prec - ediff;
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}
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/* Allocate temp space for the result. Allocate
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just vsize + ediff later??? */
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tp = (mp_ptr) TMP_ALLOC (prec * BYTES_PER_MP_LIMB);
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if (ediff >= prec)
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{
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/* V completely cancelled. */
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if (tp != up)
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MPN_COPY (rp, up, usize);
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rsize = usize;
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}
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else
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{
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/* Locate the least significant non-zero limb in (the needed
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parts of) U and V, to simplify the code below. */
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for (;;)
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{
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if (vsize == 0)
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{
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MPN_COPY (rp, up, usize);
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rsize = usize;
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goto done;
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}
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if (vp[0] != 0)
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break;
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vp++, vsize--;
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}
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for (;;)
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{
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if (usize == 0)
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{
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MPN_COPY (rp, vp, vsize);
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rsize = vsize;
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negate ^= 1;
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goto done;
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}
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if (up[0] != 0)
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break;
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up++, usize--;
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}
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/* uuuu | uuuu | uuuu | uuuu | uuuu */
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/* vvvvvvv | vv | vvvvv | v | vv */
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if (usize > ediff)
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{
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/* U and V partially overlaps. */
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if (ediff == 0)
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{
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/* Have to compare the leading limbs of u and v
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to determine whether to compute u - v or v - u. */
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if (usize > vsize)
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{
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/* uuuu */
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/* vv */
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int cmp;
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cmp = mpn_cmp (up + usize - vsize, vp, vsize);
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if (cmp >= 0)
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{
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mp_size_t size;
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size = usize - vsize;
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MPN_COPY (tp, up, size);
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mpn_sub_n (tp + size, up + size, vp, vsize);
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rsize = usize;
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}
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else
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{
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/* vv */ /* Swap U and V. */
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/* uuuu */
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mp_size_t size, i;
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size = usize - vsize;
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tp[0] = -up[0] & GMP_NUMB_MASK;
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for (i = 1; i < size; i++)
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tp[i] = ~up[i] & GMP_NUMB_MASK;
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mpn_sub_n (tp + size, vp, up + size, vsize);
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mpn_sub_1 (tp + size, tp + size, vsize, (mp_limb_t) 1);
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negate ^= 1;
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rsize = usize;
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}
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}
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else if (usize < vsize)
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{
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/* uuuu */
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/* vvvvvvv */
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int cmp;
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cmp = mpn_cmp (up, vp + vsize - usize, usize);
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if (cmp > 0)
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{
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mp_size_t size, i;
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size = vsize - usize;
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tp[0] = -vp[0] & GMP_NUMB_MASK;
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for (i = 1; i < size; i++)
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tp[i] = ~vp[i] & GMP_NUMB_MASK;
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mpn_sub_n (tp + size, up, vp + size, usize);
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mpn_sub_1 (tp + size, tp + size, usize, (mp_limb_t) 1);
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rsize = vsize;
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}
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else
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{
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/* vvvvvvv */ /* Swap U and V. */
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/* uuuu */
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/* This is the only place we can get 0.0. */
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mp_size_t size;
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size = vsize - usize;
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MPN_COPY (tp, vp, size);
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mpn_sub_n (tp + size, vp + size, up, usize);
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negate ^= 1;
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rsize = vsize;
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}
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}
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else
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{
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/* uuuu */
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/* vvvv */
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int cmp;
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cmp = mpn_cmp (up, vp + vsize - usize, usize);
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if (cmp > 0)
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{
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mpn_sub_n (tp, up, vp, usize);
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rsize = usize;
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}
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else
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{
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mpn_sub_n (tp, vp, up, usize);
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negate ^= 1;
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rsize = usize;
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/* can give zero */
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}
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}
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}
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else
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{
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if (vsize + ediff <= usize)
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{
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/* uuuu */
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/* v */
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mp_size_t size;
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size = usize - ediff - vsize;
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MPN_COPY (tp, up, size);
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mpn_sub (tp + size, up + size, usize - size, vp, vsize);
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rsize = usize;
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}
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else
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{
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/* uuuu */
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/* vvvvv */
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mp_size_t size, i;
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size = vsize + ediff - usize;
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tp[0] = -vp[0] & GMP_NUMB_MASK;
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for (i = 1; i < size; i++)
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tp[i] = ~vp[i] & GMP_NUMB_MASK;
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mpn_sub (tp + size, up, usize, vp + size, usize - ediff);
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mpn_sub_1 (tp + size, tp + size, usize, (mp_limb_t) 1);
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rsize = vsize + ediff;
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}
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}
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}
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else
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{
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/* uuuu */
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/* vv */
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mp_size_t size, i;
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size = vsize + ediff - usize;
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tp[0] = -vp[0] & GMP_NUMB_MASK;
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for (i = 1; i < vsize; i++)
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tp[i] = ~vp[i] & GMP_NUMB_MASK;
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for (i = vsize; i < size; i++)
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tp[i] = GMP_NUMB_MAX;
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mpn_sub_1 (tp + size, up, usize, (mp_limb_t) 1);
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rsize = size + usize;
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}
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/* Full normalize. Optimize later. */
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while (rsize != 0 && tp[rsize - 1] == 0)
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{
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rsize--;
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uexp--;
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}
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MPN_COPY (rp, tp, rsize);
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}
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done:
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r->_mp_size = negate ? -rsize : rsize;
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r->_mp_exp = uexp;
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TMP_FREE;
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}
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