openssl/crypto/bn/bn_shift.c

/* crypto/bn/bn_shift.c */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 *
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 *
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 *
 * 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 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 *
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``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.
 *
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#include "internal/cryptlib.h"
#include "bn_lcl.h"

int BN_lshift1(BIGNUM *r, const BIGNUM *a)
{
    register BN_ULONG *ap, *rp, t, c;
    int i;

    bn_check_top(r);
    bn_check_top(a);

    if (r != a) {
        r->neg = a->neg;
        if (bn_wexpand(r, a->top + 1) == NULL)
            return (0);
        r->top = a->top;
    } else {
        if (bn_wexpand(r, a->top + 1) == NULL)
            return (0);
    }
    ap = a->d;
    rp = r->d;
    c = 0;
    for (i = 0; i < a->top; i++) {
        t = *(ap++);
        *(rp++) = ((t << 1) | c) & BN_MASK2;
        c = (t & BN_TBIT) ? 1 : 0;
    }
    if (c) {
        *rp = 1;
        r->top++;
    }
    bn_check_top(r);
    return (1);
}

int BN_rshift1(BIGNUM *r, const BIGNUM *a)
{
    BN_ULONG *ap, *rp, t, c;
    int i, j;

    bn_check_top(r);
    bn_check_top(a);

    if (BN_is_zero(a)) {
        BN_zero(r);
        return (1);
    }
    i = a->top;
    ap = a->d;
    j = i - (ap[i - 1] == 1);
    if (a != r) {
        if (bn_wexpand(r, j) == NULL)
            return (0);
        r->neg = a->neg;
    }
    rp = r->d;
    t = ap[--i];
    c = (t & 1) ? BN_TBIT : 0;
    if (t >>= 1)
        rp[i] = t;
    while (i > 0) {
        t = ap[--i];
        rp[i] = ((t >> 1) & BN_MASK2) | c;
        c = (t & 1) ? BN_TBIT : 0;
    }
    r->top = j;
    bn_check_top(r);
    return (1);
}

int BN_lshift(BIGNUM *r, const BIGNUM *a, int n)
{
    int i, nw, lb, rb;
    BN_ULONG *t, *f;
    BN_ULONG l;

    bn_check_top(r);
    bn_check_top(a);

    if (n < 0) {
        BNerr(BN_F_BN_LSHIFT, BN_R_INVALID_SHIFT);
        return 0;
    }

    r->neg = a->neg;
    nw = n / BN_BITS2;
    if (bn_wexpand(r, a->top + nw + 1) == NULL)
        return (0);
    lb = n % BN_BITS2;
    rb = BN_BITS2 - lb;
    f = a->d;
    t = r->d;
    t[a->top + nw] = 0;
    if (lb == 0)
        for (i = a->top - 1; i >= 0; i--)
            t[nw + i] = f[i];
    else
        for (i = a->top - 1; i >= 0; i--) {
            l = f[i];
            t[nw + i + 1] |= (l >> rb) & BN_MASK2;
            t[nw + i] = (l << lb) & BN_MASK2;
        }
    memset(t, 0, sizeof(*t) * nw);
    r->top = a->top + nw + 1;
    bn_correct_top(r);
    bn_check_top(r);
    return (1);
}

int BN_rshift(BIGNUM *r, const BIGNUM *a, int n)
{
    int i, j, nw, lb, rb;
    BN_ULONG *t, *f;
    BN_ULONG l, tmp;

    bn_check_top(r);
    bn_check_top(a);

    if (n < 0) {
        BNerr(BN_F_BN_RSHIFT, BN_R_INVALID_SHIFT);
        return 0;
    }

    nw = n / BN_BITS2;
    rb = n % BN_BITS2;
    lb = BN_BITS2 - rb;
    if (nw >= a->top || a->top == 0) {
        BN_zero(r);
        return (1);
    }
    i = (BN_num_bits(a) - n + (BN_BITS2 - 1)) / BN_BITS2;
    if (r != a) {
        r->neg = a->neg;
        if (bn_wexpand(r, i) == NULL)
            return (0);
    } else {
        if (n == 0)
            return 1;           /* or the copying loop will go berserk */
    }

    f = &(a->d[nw]);
    t = r->d;
    j = a->top - nw;
    r->top = i;

    if (rb == 0) {
        for (i = j; i != 0; i--)
            *(t++) = *(f++);
    } else {
        l = *(f++);
        for (i = j - 1; i != 0; i--) {
            tmp = (l >> rb) & BN_MASK2;
            l = *(f++);
            *(t++) = (tmp | (l << lb)) & BN_MASK2;
        }
        if ((l = (l >> rb) & BN_MASK2))
            *(t) = l;
    }
    bn_check_top(r);
    return (1);
}