142 lines
3.1 KiB
C
142 lines
3.1 KiB
C
/* mpn_add -- Add two low-level integers.
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Copyright (C) 1991 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 General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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The GNU MP Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with the GNU MP Library; see the file COPYING. If not, write to
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the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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/* Add ADD1_PTR/ADD1_SIZE and ADD2_PTR/ADD2_SIZE and store the first
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ADD1_SIZE words of the result at SUM_PTR.
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Return 1 if carry out was generated, return 0 otherwise.
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Argument constraint: ADD1_SIZE >= ADD2_SIZE.
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The size of SUM can be calculated as ADD1_SIZE + the return value. */
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mp_limb
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#ifdef __STDC__
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mpn_add (mp_ptr sum_ptr,
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mp_srcptr add1_ptr, mp_size add1_size,
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mp_srcptr add2_ptr, mp_size add2_size)
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#else
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mpn_add (sum_ptr, add1_ptr, add1_size, add2_ptr, add2_size)
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mp_ptr sum_ptr;
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mp_srcptr add1_ptr;
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mp_size add1_size;
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mp_srcptr add2_ptr;
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mp_size add2_size;
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#endif
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{
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mp_limb a1, a2, sum;
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mp_size j;
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/* The loop counter and index J goes from some negative value to zero.
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This way the loops become faster. Need to offset the base pointers
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to take care of the negative indices. */
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j = -add2_size;
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if (j == 0)
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goto add2_finished;
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add1_ptr -= j;
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add2_ptr -= j;
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sum_ptr -= j;
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/* There are two do-loops, marked NON-CARRY LOOP and CARRY LOOP that
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jump between each other. The first loop is for when the previous
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addition didn't produce a carry-out; the second is for the
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complementary case. */
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/* NON-CARRY LOOP */
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do
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{
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a1 = add1_ptr[j];
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a2 = add2_ptr[j];
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sum = a1 + a2;
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sum_ptr[j] = sum;
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if (sum < a2)
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goto cy_loop;
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ncy_loop:
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j++;
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}
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while (j < 0);
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/* We have exhausted ADD2. Just copy ADD1 to SUM, and return
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0 as an indication of no carry-out. */
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add2_finished:
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/* Immediate return if the copy would be a no-op. */
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if (sum_ptr == add1_ptr)
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return 0;
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j = add2_size - add1_size;
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add1_ptr -= j;
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sum_ptr -= j;
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while (j < 0)
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{
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sum_ptr[j] = add1_ptr[j];
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j++;
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}
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return 0;
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/* CARRY LOOP */
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do
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{
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a1 = add1_ptr[j];
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a2 = add2_ptr[j];
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sum = a1 + a2 + 1;
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sum_ptr[j] = sum;
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if (sum > a2)
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goto ncy_loop;
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cy_loop:
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j++;
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}
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while (j < 0);
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j = add2_size - add1_size;
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add1_ptr -= j;
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sum_ptr -= j;
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while (j < 0)
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{
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a1 = add1_ptr[j];
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sum = a1 + 1;
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sum_ptr[j] = sum;
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if (sum > 0)
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goto copy_add1;
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j++;
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}
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return 1;
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copy_add1:
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if (sum_ptr == add1_ptr)
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return 0;
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j++;
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while (j < 0)
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{
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sum_ptr[j] = add1_ptr[j];
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j++;
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}
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return 0;
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}
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