mirror of
https://github.com/cryb-to/cryb-to.git
synced 2024-11-23 22:25:46 +00:00
a09cdc6318
The count we passed to memcmp() in mpi_eq() and mpi_eq_abs() was actually the number of significant words in the MPI, rather than the number of bytes we wanted to compare. Multiply by 4 to get the correct value.
To make the intent of the code more apparent, introduce a private MPI_MSW() macro which evaluates to the number of significant words (or 1-based index of the most significant word). This also comes in handy in mpi_{add,sub,mul}_abs().
Add a couple of test cases which not only demonstrate the bug we fixed here but also demonstrate why we must compare whole words: on a big-endian machine, we would be comparing the unused upper bytes of the first and only word instead of the lower bytes which actually hold a value...
104 lines
3.2 KiB
C
104 lines
3.2 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 <stddef.h>
|
|
#include <stdint.h>
|
|
#include <strings.h>
|
|
|
|
#include <cryb/bitwise.h>
|
|
#include <cryb/mpi.h>
|
|
|
|
#include "cryb_mpi_impl.h"
|
|
|
|
/*
|
|
* Store the product of the absolutes values of A and B in X.
|
|
*
|
|
* Note: this is loosely based on HAC 14.2.3. However, the first
|
|
* paragraph speaks of x and y having n and t digits respectively, with
|
|
* the most significant digits being x[n - 1] and y[t - 1], but the rest
|
|
* of the section refers to x and y having n + 1 and t + 1 digits. We
|
|
* follow the former convention, but use a and b instead of n and t to
|
|
* distance ourselves from this confusing text.
|
|
*/
|
|
int
|
|
mpi_mul_abs(cryb_mpi *X, const cryb_mpi *A, const cryb_mpi *B)
|
|
{
|
|
cryb_mpi *P, T = CRYB_MPI_ZERO;
|
|
uint64_t p;
|
|
unsigned int a, b, i, j;
|
|
uint32_t c;
|
|
|
|
/*
|
|
* Trivial cases: A and / or B is zero.
|
|
*/
|
|
if (A->msb == 0 || B->msb == 0) {
|
|
mpi_zero(X);
|
|
return (0);
|
|
}
|
|
|
|
/*
|
|
* Unlike addition or subtraction, we can't multiply in place, so
|
|
* if the destination is identical with one of the operands, we
|
|
* will have to use temporary storage. Either way, make sure we
|
|
* have enough room for the product.
|
|
*/
|
|
P = (X == A || X == B) ? &T : X;
|
|
mpi_zero(P);
|
|
a = MPI_MSW(A);
|
|
b = MPI_MSW(B);
|
|
if (mpi_grow(P, (a + b) * 32) != 0)
|
|
return (-1);
|
|
|
|
/*
|
|
* Multiply...
|
|
*/
|
|
for (i = 0; i < b; ++i) {
|
|
for (c = j = 0; j < a; ++j) {
|
|
p = 1ULL * A->words[j] * B->words[i] + c;
|
|
P->words[i + j] += p & 0xffffffffUL;
|
|
c = p >> 32;
|
|
}
|
|
P->words[i + j] = c;
|
|
}
|
|
if (P->words[i = a + b - 1] == 0)
|
|
--i;
|
|
P->msb = i * 32 + flsl(P->words[i]);
|
|
|
|
/*
|
|
* If we used temporary storage, copy back and clean up.
|
|
*/
|
|
if (P == &T) {
|
|
cryb_mpi_swap(X, P);
|
|
cryb_mpi_destroy(P);
|
|
}
|
|
|
|
return (0);
|
|
}
|