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/*
* Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include "internal/cryptlib.h"
#include "bn_local.h"
BN_ULONG BN_mod_word(const BIGNUM *a, BN_ULONG w)
{
#ifndef BN_LLONG
BN_ULONG ret = 0;
#else
BN_ULLONG ret = 0;
#endif
int i;
if (w == 0)
return (BN_ULONG)-1;
#ifndef BN_LLONG
/*
* If |w| is too long and we don't have BN_ULLONG then we need to fall
* back to using BN_div_word
*/
if (w > ((BN_ULONG)1 << BN_BITS4)) {
BIGNUM *tmp = BN_dup(a);
if (tmp == NULL)
return (BN_ULONG)-1;
ret = BN_div_word(tmp, w);
BN_free(tmp);
return ret;
}
#endif
bn_check_top(a);
w &= BN_MASK2;
for (i = a->top - 1; i >= 0; i--) {
#ifndef BN_LLONG
/*
* We can assume here that | w <= ((BN_ULONG)1 << BN_BITS4) | and so
* | ret < ((BN_ULONG)1 << BN_BITS4) | and therefore the shifts here are
* safe and will not overflow
*/
ret = ((ret << BN_BITS4) | ((a->d[i] >> BN_BITS4) & BN_MASK2l)) % w;
ret = ((ret << BN_BITS4) | (a->d[i] & BN_MASK2l)) % w;
#else
ret = (BN_ULLONG) (((ret << (BN_ULLONG) BN_BITS2) | a->d[i]) %
(BN_ULLONG) w);
#endif
}
return (BN_ULONG)ret;
}
BN_ULONG BN_div_word(BIGNUM *a, BN_ULONG w)
{
BN_ULONG ret = 0;
int i, j;
bn_check_top(a);
w &= BN_MASK2;
if (!w)
/* actually this an error (division by zero) */
return (BN_ULONG)-1;
if (a->top == 0)
return 0;
/* normalize input (so bn_div_words doesn't complain) */
j = BN_BITS2 - BN_num_bits_word(w);
w <<= j;
if (!BN_lshift(a, a, j))
return (BN_ULONG)-1;
for (i = a->top - 1; i >= 0; i--) {
BN_ULONG l, d;
l = a->d[i];
d = bn_div_words(ret, l, w);
ret = (l - ((d * w) & BN_MASK2)) & BN_MASK2;
a->d[i] = d;
}
if ((a->top > 0) && (a->d[a->top - 1] == 0))
a->top--;
ret >>= j;
if (!a->top)
a->neg = 0; /* don't allow negative zero */
bn_check_top(a);
return ret;
}
int BN_add_word(BIGNUM *a, BN_ULONG w)
{
BN_ULONG l;
int i;
bn_check_top(a);
w &= BN_MASK2;
/* degenerate case: w is zero */
if (!w)
return 1;
/* degenerate case: a is zero */
if (BN_is_zero(a))
return BN_set_word(a, w);
/* handle 'a' when negative */
if (a->neg) {
a->neg = 0;
i = BN_sub_word(a, w);
if (!BN_is_zero(a))
a->neg = !(a->neg);
return i;
}
for (i = 0; w != 0 && i < a->top; i++) {
a->d[i] = l = (a->d[i] + w) & BN_MASK2;
w = (w > l) ? 1 : 0;
}
if (w && i == a->top) {
if (bn_wexpand(a, a->top + 1) == NULL)
return 0;
a->top++;
a->d[i] = w;
}
bn_check_top(a);
return 1;
}
int BN_sub_word(BIGNUM *a, BN_ULONG w)
{
int i;
bn_check_top(a);
w &= BN_MASK2;
/* degenerate case: w is zero */
if (!w)
return 1;
/* degenerate case: a is zero */
if (BN_is_zero(a)) {
i = BN_set_word(a, w);
if (i != 0)
BN_set_negative(a, 1);
return i;
}
/* handle 'a' when negative */
if (a->neg) {
a->neg = 0;
i = BN_add_word(a, w);
a->neg = 1;
return i;
}
if ((a->top == 1) && (a->d[0] < w)) {
a->d[0] = w - a->d[0];
a->neg = 1;
return 1;
}
i = 0;
for (;;) {
if (a->d[i] >= w) {
a->d[i] -= w;
break;
} else {
a->d[i] = (a->d[i] - w) & BN_MASK2;
i++;
w = 1;
}
}
if ((a->d[i] == 0) && (i == (a->top - 1)))
a->top--;
bn_check_top(a);
return 1;
}
int BN_mul_word(BIGNUM *a, BN_ULONG w)
{
BN_ULONG ll;
bn_check_top(a);
w &= BN_MASK2;
if (a->top) {
if (w == 0)
BN_zero(a);
else {
ll = bn_mul_words(a->d, a->d, a->top, w);
if (ll) {
if (bn_wexpand(a, a->top + 1) == NULL)
return 0;
a->d[a->top++] = ll;
}
}
}
bn_check_top(a);
return 1;
}
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