mirror of
https://github.com/cryb-to/cryb-to.git
synced 2024-12-27 15:01:07 +00:00
83 lines
2.8 KiB
C
83 lines
2.8 KiB
C
/*
|
|
* Copyright (c) 2014 Dag-Erling Smørgrav
|
|
* All rights reserved.
|
|
*
|
|
* Redistribution and use in source and binary forms, with or without
|
|
* modification, are permitted provided that the following conditions
|
|
* are met:
|
|
* 1. Redistributions of source code must retain the above copyright
|
|
* notice, this list of conditions and the following disclaimer.
|
|
* 2. Redistributions in binary form must reproduce the above copyright
|
|
* notice, this list of conditions and the following disclaimer in the
|
|
* documentation and/or other materials provided with the distribution.
|
|
* 3. The name of the author may not be used to endorse or promote
|
|
* products derived from this software without specific prior written
|
|
* permission.
|
|
*
|
|
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
|
|
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
|
|
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
* SUCH DAMAGE.
|
|
*/
|
|
|
|
#include "cryb/impl.h"
|
|
|
|
#include <stdint.h>
|
|
#include <stdlib.h>
|
|
|
|
#include <cryb/mpi.h>
|
|
|
|
/*
|
|
* Store the difference between the absolute values of A and B in X.
|
|
* XXX safe for either A or B to be the same object as X but not both
|
|
*/
|
|
int
|
|
mpi_sub_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B)
|
|
{
|
|
unsigned int i;
|
|
uint32_t c;
|
|
|
|
if (X == B)
|
|
B = A, A = X;
|
|
if (X != A)
|
|
mpi_copy(X, A);
|
|
/* 0 - 0 = 0 */
|
|
if (X->msb == 0 && B->msb == 0)
|
|
return (0);
|
|
/* make room */
|
|
if (mpi_grow(X, X->msb) != 0 || mpi_grow(X, B->msb) != 0)
|
|
return (-1);
|
|
/* subtract B from X word by word until we run out of B */
|
|
for (c = i = 0; i < (B->msb + 31) / 32; ++i) {
|
|
// fprintf(stderr, "0x%08x + 0x%08x (%u)", X->words[i], B->words[i], c);
|
|
X->words[i] -= c;
|
|
c = (X->words[i] > c);
|
|
X->words[i] -= B->words[i];
|
|
c += (X->words[i] > B->words[i]);
|
|
// fprintf(stderr, " = 0x%08x (%u)\n", X->words[i], c);
|
|
}
|
|
/* keep propagating carry */
|
|
while (c) {
|
|
// fprintf(stderr, "0x%08x + 0x%08x (%u)", X->words[i], 0, c);
|
|
X->words[i] -= c;
|
|
c = (X->words[i] > c);
|
|
// fprintf(stderr, " = 0x%08x (%u)\n", X->words[i], c);
|
|
++i;
|
|
}
|
|
if (X->words[i] == 0)
|
|
--i;
|
|
/* compute msb of msw */
|
|
for (X->msb = 31; X->msb > 0; --X->msb)
|
|
if (X->words[i] & (1 << X->msb))
|
|
break;
|
|
/* add msw offset */
|
|
X->msb += i * 32 + 1;
|
|
return (0);
|
|
}
|