403 lines
8.8 KiB
C
403 lines
8.8 KiB
C
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/* mpf_sub -- Subtract two floats.
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Copyright (C) 1993, 1994, 1995, 1996 Free Software Foundation, 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 Library General Public License as published by
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the Free Software Foundation; either version 2 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 Library General Public
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License for more details.
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You should have received a copy of the GNU Library 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., 59 Temple Place - Suite 330, Boston,
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MA 02111-1307, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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void
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#if __STDC__
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mpf_sub (mpf_ptr r, mpf_srcptr u, mpf_srcptr v)
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#else
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mpf_sub (r, u, v)
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mpf_ptr r;
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mpf_srcptr u;
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mpf_srcptr v;
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#endif
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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 exp;
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mp_size_t ediff;
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int negate;
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TMP_DECL (marker);
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usize = u->_mp_size;
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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 (usize == 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 (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 ((usize ^ 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 (r, u, &v_negated);
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return;
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}
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TMP_MARK (marker);
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/* Signs are now known to be the same. */
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negate = usize < 0;
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/* Make U be the operand with the largest exponent. */
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if (u->_mp_exp < v->_mp_exp)
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{
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mpf_srcptr t;
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t = u; u = v; v = t;
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negate ^= 1;
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usize = u->_mp_size;
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vsize = v->_mp_size;
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}
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usize = ABS (usize);
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vsize = ABS (vsize);
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up = u->_mp_d;
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vp = v->_mp_d;
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rp = r->_mp_d;
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prec = r->_mp_prec + 1;
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exp = u->_mp_exp;
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ediff = u->_mp_exp - v->_mp_exp;
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/* If ediff is 0 or 1, we might have a situation where the operands are
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extremely close. We need to scan the operands from the most significant
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end ignore the initial parts that are equal. */
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if (ediff <= 1)
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{
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if (ediff == 0)
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{
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/* Skip leading limbs in U and V that are equal. */
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if (up[usize - 1] == vp[vsize - 1])
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{
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/* This loop normally exits immediately. Optimize for that. */
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do
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{
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usize--;
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vsize--;
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exp--;
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if (usize == 0)
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{
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rsize = vsize;
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tp = (mp_ptr) vp;
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negate ^= 1;
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goto normalize;
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}
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if (vsize == 0)
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{
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rsize = usize;
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tp = (mp_ptr) up;
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goto normalize;
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}
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}
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while (up[usize - 1] == vp[vsize - 1]);
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}
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if (up[usize - 1] < vp[vsize - 1])
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{
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/* For simplicity, swap U and V. Note that since the loop above
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wouldn't have exited unless up[usize - 1] and vp[vsize - 1]
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were non-equal, this if-statement catches all cases where U
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is smaller than V. */
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{ mp_srcptr tp = up; up = vp; vp = tp; }
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{ mp_size_t tsize = usize; usize = vsize; vsize = tsize; }
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negate ^= 1;
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/* negating ediff not necessary since it is 0. */
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}
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/* Check for
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x+1 00000000 ...
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x ffffffff ... */
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if (up[usize - 1] != vp[vsize - 1] + 1)
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goto general_case;
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usize--;
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vsize--;
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exp--;
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}
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else /* ediff == 1 */
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{
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/* Check for
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1 00000000 ...
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0 ffffffff ... */
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if (up[usize - 1] != 1 || vp[vsize - 1] != ~(mp_limb_t) 0
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|| (usize >= 2 && up[usize - 2] != 0))
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goto general_case;
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usize--;
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exp--;
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}
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/* Skip sequences of 00000000/ffffffff */
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while (vsize != 0 && usize != 0 && up[usize - 1] == 0
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&& vp[vsize - 1] == ~(mp_limb_t) 0)
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{
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usize--;
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vsize--;
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exp--;
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}
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if (usize == 0)
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{
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while (vsize != 0 && vp[vsize - 1] == ~(mp_limb_t) 0)
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{
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vsize--;
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exp--;
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}
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}
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if (usize > prec - 1)
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{
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up += usize - (prec - 1);
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usize = prec - 1;
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}
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if (vsize > prec - 1)
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{
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vp += vsize - (prec - 1);
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vsize = prec - 1;
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}
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tp = (mp_ptr) TMP_ALLOC (prec * BYTES_PER_MP_LIMB);
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{
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mp_limb_t cy_limb;
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if (vsize == 0)
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{
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mp_size_t size, i;
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size = usize;
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for (i = 0; i < size; i++)
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tp[i] = up[i];
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tp[size] = 1;
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rsize = size + 1;
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exp++;
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goto normalize;
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}
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if (usize == 0)
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{
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mp_size_t size, i;
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size = vsize;
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for (i = 0; i < size; i++)
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tp[i] = ~vp[i];
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cy_limb = 1 - mpn_add_1 (tp, tp, vsize, (mp_limb_t) 1);
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rsize = vsize;
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if (cy_limb == 0)
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{
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tp[rsize] = 1;
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rsize++;
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exp++;
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}
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goto normalize;
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}
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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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mp_size_t size;
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size = usize - vsize;
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MPN_COPY (tp, up, size);
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cy_limb = mpn_sub_n (tp + size, up + size, vp, vsize);
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rsize = usize;
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}
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else /* (usize < vsize) */
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{
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/* uuuu */
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/* vvvvvvv */
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mp_size_t size, i;
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size = vsize - usize;
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for (i = 0; i < size; i++)
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tp[i] = ~vp[i];
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cy_limb = mpn_sub_n (tp + size, up, vp + size, usize);
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cy_limb+= mpn_sub_1 (tp + size, tp + size, usize, (mp_limb_t) 1);
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cy_limb-= mpn_add_1 (tp, tp, vsize, (mp_limb_t) 1);
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rsize = vsize;
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}
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if (cy_limb == 0)
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{
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tp[rsize] = 1;
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rsize++;
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exp++;
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}
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goto normalize;
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}
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}
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general_case:
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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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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 /* (usize < vsize) */
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{
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/* uuuu */
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/* vvvvvvv */
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mp_size_t size, i;
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size = vsize - usize;
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tp[0] = -vp[0];
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for (i = 1; i < size; i++)
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tp[i] = ~vp[i];
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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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}
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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];
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for (i = 1; i < size; i++)
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tp[i] = ~vp[i];
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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];
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for (i = 1; i < vsize; i++)
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tp[i] = ~vp[i];
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for (i = vsize; i < size; i++)
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tp[i] = ~(mp_limb_t) 0;
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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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normalize:
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/* Full normalize. Optimize later. */
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while (rsize != 0 && tp[rsize - 1] == 0)
|
||
|
|
{
|
||
|
|
rsize--;
|
||
|
|
exp--;
|
||
|
|
}
|
||
|
|
MPN_COPY (rp, tp, rsize);
|
||
|
|
}
|
||
|
|
|
||
|
|
done:
|
||
|
|
r->_mp_size = negate ? -rsize : rsize;
|
||
|
|
r->_mp_exp = exp;
|
||
|
|
TMP_FREE (marker);
|
||
|
|
}
|