/* mpi-div.c - MPI functions
* Copyright (C) 1994, 1996, 1998, 2001, 2002,
* 2003 Free Software Foundation, Inc.
*
* This file is part of Libgcrypt.
*
* Libgcrypt is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* Libgcrypt 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*
* Note: This code is heavily based on the GNU MP Library.
* Actually it's the same code with only minor changes in the
* way the data is stored; this is to support the abstraction
* of an optional secure memory allocation which may be used
* to avoid revealing of sensitive data due to paging etc.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include "mpi-internal.h"
#include "longlong.h"
#include "g10lib.h"
void
_gcry_mpi_fdiv_r( gcry_mpi_t rem, gcry_mpi_t dividend, gcry_mpi_t divisor )
{
int divisor_sign = divisor->sign;
gcry_mpi_t temp_divisor = NULL;
/* We need the original value of the divisor after the remainder has been
* preliminary calculated. We have to copy it to temporary space if it's
* the same variable as REM. */
if( rem == divisor ) {
temp_divisor = mpi_copy( divisor );
divisor = temp_divisor;
}
_gcry_mpi_tdiv_r( rem, dividend, divisor );
if( ((divisor_sign?1:0) ^ (dividend->sign?1:0)) && rem->nlimbs )
mpi_add (rem, rem, divisor);
if( temp_divisor )
mpi_free(temp_divisor);
}
/****************
* Division rounding the quotient towards -infinity.
* The remainder gets the same sign as the denominator.
* rem is optional
*/
ulong
_gcry_mpi_fdiv_r_ui( gcry_mpi_t rem, gcry_mpi_t dividend, ulong divisor )
{
mpi_limb_t rlimb;
rlimb = _gcry_mpih_mod_1( dividend->d, dividend->nlimbs, divisor );
if( rlimb && dividend->sign )
rlimb = divisor - rlimb;
if( rem ) {
rem->d[0] = rlimb;
rem->nlimbs = rlimb? 1:0;
}
return rlimb;
}
void
_gcry_mpi_fdiv_q( gcry_mpi_t quot, gcry_mpi_t dividend, gcry_mpi_t divisor )
{
gcry_mpi_t tmp = mpi_alloc( mpi_get_nlimbs(quot) );
_gcry_mpi_fdiv_qr( quot, tmp, dividend, divisor);
mpi_free(tmp);
}
void
_gcry_mpi_fdiv_qr( gcry_mpi_t quot, gcry_mpi_t rem, gcry_mpi_t dividend, gcry_mpi_t divisor )
{
int divisor_sign = divisor->sign;
gcry_mpi_t temp_divisor = NULL;
if( quot == divisor || rem == divisor ) {
temp_divisor = mpi_copy( divisor );
divisor = temp_divisor;
}
_gcry_mpi_tdiv_qr( quot, rem, dividend, divisor );
if( (divisor_sign ^ dividend->sign) && rem->nlimbs ) {
mpi_sub_ui( quot, quot, 1 );
mpi_add( rem, rem, divisor);
}
if( temp_divisor )
mpi_free(temp_divisor);
}
/* If den == quot, den needs temporary storage.
* If den == rem, den needs temporary storage.
* If num == quot, num needs temporary storage.
* If den has temporary storage, it can be normalized while being copied,
* i.e no extra storage should be allocated.
*/
void
_gcry_mpi_tdiv_r( gcry_mpi_t rem, gcry_mpi_t num, gcry_mpi_t den)
{
_gcry_mpi_tdiv_qr(NULL, rem, num, den );
}
void
_gcry_mpi_tdiv_qr( gcry_mpi_t quot, gcry_mpi_t rem, gcry_mpi_t num, gcry_mpi_t den)
{
mpi_ptr_t np, dp;
mpi_ptr_t qp, rp;
mpi_size_t nsize = num->nlimbs;
mpi_size_t dsize = den->nlimbs;
mpi_size_t qsize, rsize;
mpi_size_t sign_remainder = num->sign;
mpi_size_t sign_quotient = num->sign ^ den->sign;
unsigned normalization_steps;
mpi_limb_t q_limb;
mpi_ptr_t marker[5];
unsigned int marker_nlimbs[5];
int markidx=0;
/* Ensure space is enough for quotient and remainder.
* We need space for an extra limb in the remainder, because it's
* up-shifted (normalized) below. */
rsize = nsize + 1;
mpi_resize( rem, rsize);
qsize = rsize - dsize; /* qsize cannot be bigger than this. */
if( qsize <= 0 ) {
if( num != rem ) {
rem->nlimbs = num->nlimbs;
rem->sign = num->sign;
MPN_COPY(rem->d, num->d, nsize);
}
if( quot ) {
/* This needs to follow the assignment to rem, in case the
* numerator and quotient are the same. */
quot->nlimbs = 0;
quot->sign = 0;
}
return;
}
if( quot )
mpi_resize( quot, qsize);
if (!dsize)
_gcry_divide_by_zero();
/* Read pointers here, when reallocation is finished. */
np = num->d;
dp = den->d;
rp = rem->d;
/* Optimize division by a single-limb divisor. */
if( dsize == 1 ) {
mpi_limb_t rlimb;
if( quot ) {
qp = quot->d;
rlimb = _gcry_mpih_divmod_1( qp, np, nsize, dp[0] );
qsize -= qp[qsize - 1] == 0;
quot->nlimbs = qsize;
quot->sign = sign_quotient;
}
else
rlimb = _gcry_mpih_mod_1( np, nsize, dp[0] );
rp[0] = rlimb;
rsize = rlimb != 0?1:0;
rem->nlimbs = rsize;
rem->sign = sign_remainder;
return;
}
if( quot ) {
qp = quot->d;
/* Make sure QP and NP point to different objects. Otherwise the
* numerator would be gradually overwritten by the quotient limbs. */
if(qp == np) { /* Copy NP object to temporary space. */
marker_nlimbs[markidx] = nsize;
np = marker[markidx++] = mpi_alloc_limb_space(nsize,
mpi_is_secure(quot));
MPN_COPY(np, qp, nsize);
}
}
else /* Put quotient at top of remainder. */
qp = rp + dsize;
count_leading_zeros( normalization_steps, dp[dsize - 1] );
/* Normalize the denominator, i.e. make its most significant bit set by
* shifting it NORMALIZATION_STEPS bits to the left. Also shift the
* numerator the same number of steps (to keep the quotient the same!).
*/
if( normalization_steps ) {
mpi_ptr_t tp;
mpi_limb_t nlimb;
/* Shift up the denominator setting the most significant bit of
* the most significant word. Use temporary storage not to clobber
* the original contents of the denominator. */
marker_nlimbs[markidx] = dsize;
tp = marker[markidx++] = mpi_alloc_limb_space(dsize,mpi_is_secure(den));
_gcry_mpih_lshift( tp, dp, dsize, normalization_steps );
dp = tp;
/* Shift up the numerator, possibly introducing a new most
* significant word. Move the shifted numerator in the remainder
* meanwhile. */
nlimb = _gcry_mpih_lshift(rp, np, nsize, normalization_steps);
if( nlimb ) {
rp[nsize] = nlimb;
rsize = nsize + 1;
}
else
rsize = nsize;
}
else {
/* The denominator is already normalized, as required. Copy it to
* temporary space if it overlaps with the quotient or remainder. */
if( dp == rp || (quot && (dp == qp))) {
mpi_ptr_t tp;
marker_nlimbs[markidx] = dsize;
tp = marker[markidx++] = mpi_alloc_limb_space(dsize,
mpi_is_secure(den));
MPN_COPY( tp, dp, dsize );
dp = tp;
}
/* Move the numerator to the remainder. */
if( rp != np )
MPN_COPY(rp, np, nsize);
rsize = nsize;
}
q_limb = _gcry_mpih_divrem( qp, 0, rp, rsize, dp, dsize );
if( quot ) {
qsize = rsize - dsize;
if(q_limb) {
qp[qsize] = q_limb;
qsize += 1;
}
quot->nlimbs = qsize;
quot->sign = sign_quotient;
}
rsize = dsize;
MPN_NORMALIZE (rp, rsize);
if( normalization_steps && rsize ) {
_gcry_mpih_rshift(rp, rp, rsize, normalization_steps);
rsize -= rp[rsize - 1] == 0?1:0;
}
rem->nlimbs = rsize;
rem->sign = sign_remainder;
while( markidx )
{
markidx--;
_gcry_mpi_free_limb_space (marker[markidx], marker_nlimbs[markidx]);
}
}
void
_gcry_mpi_tdiv_q_2exp( gcry_mpi_t w, gcry_mpi_t u, unsigned int count )
{
mpi_size_t usize, wsize;
mpi_size_t limb_cnt;
usize = u->nlimbs;
limb_cnt = count / BITS_PER_MPI_LIMB;
wsize = usize - limb_cnt;
if( limb_cnt >= usize )
w->nlimbs = 0;
else {
mpi_ptr_t wp;
mpi_ptr_t up;
RESIZE_IF_NEEDED( w, wsize );
wp = w->d;
up = u->d;
count %= BITS_PER_MPI_LIMB;
if( count ) {
_gcry_mpih_rshift( wp, up + limb_cnt, wsize, count );
wsize -= !wp[wsize - 1];
}
else {
MPN_COPY_INCR( wp, up + limb_cnt, wsize);
}
w->nlimbs = wsize;
}
}
/****************
* Check whether dividend is divisible by divisor
* (note: divisor must fit into a limb)
*/
int
_gcry_mpi_divisible_ui(gcry_mpi_t dividend, ulong divisor )
{
return !_gcry_mpih_mod_1( dividend->d, dividend->nlimbs, divisor );
}
void
_gcry_mpi_div (gcry_mpi_t quot, gcry_mpi_t rem, gcry_mpi_t dividend,
gcry_mpi_t divisor, int round)
{
if (!round)
{
if (!rem)
{
gcry_mpi_t tmp = mpi_alloc (mpi_get_nlimbs(quot));
_gcry_mpi_tdiv_qr (quot, tmp, dividend, divisor);
mpi_free (tmp);
}
else
_gcry_mpi_tdiv_qr (quot, rem, dividend, divisor);
}
else if (round < 0)
{
if (!rem)
_gcry_mpi_fdiv_q (quot, dividend, divisor);
else if (!quot)
_gcry_mpi_fdiv_r (rem, dividend, divisor);
else
_gcry_mpi_fdiv_qr (quot, rem, dividend, divisor);
}
else
log_bug ("mpi rounding to ceiling not yet implemented\n");
}
