mirror of
https://github.com/cryb-to/cryb-to.git
synced 2024-11-15 02:05:40 +00:00
115 lines
3.3 KiB
C
115 lines
3.3 KiB
C
/*
|
|
* Copyright (c) 2017 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 <errno.h>
|
|
#include <stddef.h>
|
|
#include <stdint.h>
|
|
#include <strings.h>
|
|
|
|
#include <cryb/bitwise.h>
|
|
#include <cryb/mpi.h>
|
|
|
|
#include "cryb_mpi_impl.h"
|
|
|
|
/*
|
|
* Store the quotient and remainder of A divided by B in Q and R.
|
|
*
|
|
* Assumes Q != R, but any combination of {Q,R} == {A,B} is fine. Either
|
|
* Q or R or both may be NULL, althought the latter is pointless.
|
|
*/
|
|
int
|
|
mpi_div_abs(cryb_mpi *Q, cryb_mpi *R, const cryb_mpi *A, const cryb_mpi *B)
|
|
{
|
|
cryb_mpi AA = CRYB_MPI_ZERO, QQ = CRYB_MPI_ZERO;
|
|
int cmp;
|
|
|
|
/* trivial cases */
|
|
if (B->msb == 0) {
|
|
/* divide something by zero */
|
|
errno = EINVAL;
|
|
return (-1);
|
|
} else if (A->msb == 0) {
|
|
/* divide zero by something */
|
|
if (Q != NULL)
|
|
mpi_zero(Q);
|
|
if (R != NULL)
|
|
mpi_zero(R);
|
|
return (0);
|
|
} else if (B->msb == 1) {
|
|
/* divide something by one */
|
|
if (Q != A && Q != NULL && mpi_copy(Q, A) != 0)
|
|
return (-1);
|
|
if (R != NULL)
|
|
mpi_zero(R);
|
|
return (0);
|
|
} else if ((cmp = mpi_cmp_abs(A, B)) == 0) {
|
|
/* divide something by itself */
|
|
if (Q != NULL)
|
|
mpi_set(Q, 1);
|
|
if (R != NULL)
|
|
mpi_zero(R);
|
|
return (0);
|
|
} else if (cmp < 0) {
|
|
/* divide something by something larger */
|
|
if (Q != NULL)
|
|
mpi_zero(Q);
|
|
if (R != A && R != NULL && mpi_copy(R, A) != 0)
|
|
return (-1);
|
|
return (0);
|
|
}
|
|
|
|
/* division is destructive, so we work on copies */
|
|
if (mpi_copy(&AA, A) != 0)
|
|
return (-1);
|
|
mpi_zero(&QQ);
|
|
|
|
/*
|
|
* Repeatedly subtract B from A until they are the same length,
|
|
* then one last time if A is still greater than B.
|
|
*/
|
|
while (AA.msb > B->msb) {
|
|
mpi_sub_abs(&AA, &AA, B);
|
|
mpi_inc_abs(&QQ);
|
|
}
|
|
if (mpi_cmp_abs(&AA, B) >= 0) {
|
|
mpi_sub_abs(&AA, &AA, B);
|
|
mpi_inc_abs(&QQ);
|
|
}
|
|
|
|
/* store result where requested and clean up */
|
|
if (Q != NULL)
|
|
mpi_swap(Q, &QQ);
|
|
if (R != NULL)
|
|
mpi_swap(R, &AA);
|
|
mpi_destroy(&AA);
|
|
mpi_destroy(&QQ);
|
|
return (0);
|
|
}
|