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/* mpn_add -- Add two low-level integers.
Copyright (C) 1991 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 General Public License as published by
the Free Software Foundation; either version 2, 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with the GNU MP Library; see the file COPYING. If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
#include "gmp.h"
#include "gmp-impl.h"
/* Add ADD1_PTR/ADD1_SIZE and ADD2_PTR/ADD2_SIZE and store the first
ADD1_SIZE words of the result at SUM_PTR.
Return 1 if carry out was generated, return 0 otherwise.
Argument constraint: ADD1_SIZE >= ADD2_SIZE.
The size of SUM can be calculated as ADD1_SIZE + the return value. */
mp_limb
#ifdef __STDC__
mpn_add (mp_ptr sum_ptr,
mp_srcptr add1_ptr, mp_size add1_size,
mp_srcptr add2_ptr, mp_size add2_size)
#else
mpn_add (sum_ptr, add1_ptr, add1_size, add2_ptr, add2_size)
mp_ptr sum_ptr;
mp_srcptr add1_ptr;
mp_size add1_size;
mp_srcptr add2_ptr;
mp_size add2_size;
#endif
{
mp_limb a1, a2, sum;
mp_size j;
/* The loop counter and index J goes from some negative value to zero.
This way the loops become faster. Need to offset the base pointers
to take care of the negative indices. */
j = -add2_size;
if (j == 0)
goto add2_finished;
add1_ptr -= j;
add2_ptr -= j;
sum_ptr -= j;
/* There are two do-loops, marked NON-CARRY LOOP and CARRY LOOP that
jump between each other. The first loop is for when the previous
addition didn't produce a carry-out; the second is for the
complementary case. */
/* NON-CARRY LOOP */
do
{
a1 = add1_ptr[j];
a2 = add2_ptr[j];
sum = a1 + a2;
sum_ptr[j] = sum;
if (sum < a2)
goto cy_loop;
ncy_loop:
j++;
}
while (j < 0);
/* We have exhausted ADD2. Just copy ADD1 to SUM, and return
0 as an indication of no carry-out. */
add2_finished:
/* Immediate return if the copy would be a no-op. */
if (sum_ptr == add1_ptr)
return 0;
j = add2_size - add1_size;
add1_ptr -= j;
sum_ptr -= j;
while (j < 0)
{
sum_ptr[j] = add1_ptr[j];
j++;
}
return 0;
/* CARRY LOOP */
do
{
a1 = add1_ptr[j];
a2 = add2_ptr[j];
sum = a1 + a2 + 1;
sum_ptr[j] = sum;
if (sum > a2)
goto ncy_loop;
cy_loop:
j++;
}
while (j < 0);
j = add2_size - add1_size;
add1_ptr -= j;
sum_ptr -= j;
while (j < 0)
{
a1 = add1_ptr[j];
sum = a1 + 1;
sum_ptr[j] = sum;
if (sum > 0)
goto copy_add1;
j++;
}
return 1;
copy_add1:
if (sum_ptr == add1_ptr)
return 0;
j++;
while (j < 0)
{
sum_ptr[j] = add1_ptr[j];
j++;
}
return 0;
}
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