/*

 * Copyright 1995-2025 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 <assert.h>

#include "internal/cryptlib.h"

#include "bn_local.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_BITS2 - 1);

    }

    *rp = c;

    r->top += (int)c;

    bn_check_top(r);

    return 1;

}

int BN_rshift1(BIGNUM *r, const BIGNUM *a)

{

    BN_ULONG *ap, *rp, t, c;

    int i;

    bn_check_top(r);

    bn_check_top(a);

    if (BN_is_zero(a)) {

        BN_zero(r);

        return 1;

    }

    i = a->top;

    ap = a->d;

    if (a != r) {

        if (bn_wexpand(r, i) == NULL)

            return 0;

        r->neg = a->neg;

    }

    rp = r->d;

    r->top = i;

    t = ap[--i];

    rp[i] = t >> 1;

    c = t << (BN_BITS2 - 1);

    r->top -= (t == 1);

    while (i > 0) {

        t = ap[--i];

        rp[i] = ((t >> 1) & BN_MASK2) | c;

        c = t << (BN_BITS2 - 1);

    }

    if (!r->top)

        r->neg = 0; /* don't allow negative zero */

    bn_check_top(r);

    return 1;

}

int BN_lshift(BIGNUM *r, const BIGNUM *a, int n)

{

    int ret;

    if (n < 0) {

        ERR_raise(ERR_LIB_BN, BN_R_INVALID_SHIFT);

        return 0;

    }

    ret = bn_lshift_fixed_top(r, a, n);

    bn_correct_top(r);

    bn_check_top(r);

    return ret;

}

/*

 * In respect to shift factor the execution time is invariant of

 * |n % BN_BITS2|, but not |n / BN_BITS2|. Or in other words pre-condition

 * for constant-time-ness is |n < BN_BITS2| or |n / BN_BITS2| being

 * non-secret.

 */

int bn_lshift_fixed_top(BIGNUM *r, const BIGNUM *a, int n)

{

    int i, nw;

    unsigned int lb, rb;

    BN_ULONG *t, *f;

    BN_ULONG l, m, rmask = 0;

    assert(n >= 0);

    bn_check_top(r);

    bn_check_top(a);

    nw = n / BN_BITS2;

    if (bn_wexpand(r, a->top + nw + 1) == NULL)

        return 0;

    if (a->top != 0) {

        lb = (unsigned int)n % BN_BITS2;

        rb = BN_BITS2 - lb;

        rb %= BN_BITS2; /* say no to undefined behaviour */

        rmask = (BN_ULONG)0 - rb; /* rmask = 0 - (rb != 0) */

        rmask |= rmask >> 8;

        f = &(a->d[0]);

        t = &(r->d[nw]);

        l = f[a->top - 1];

        t[a->top] = (l >> rb) & rmask;

        for (i = a->top - 1; i > 0; i--) {

            m = l << lb;

            l = f[i - 1];

            t[i] = (m | ((l >> rb) & rmask)) & BN_MASK2;

        }

        t[0] = (l << lb) & BN_MASK2;

    } else {

        /* shouldn't happen, but formally required */

        r->d[nw] = 0;

    }

    if (nw != 0)

        memset(r->d, 0, sizeof(*t) * nw);

    r->neg = a->neg;

    r->top = a->top + nw + 1;

    r->flags |= BN_FLG_FIXED_TOP;

    return 1;

}

int BN_rshift(BIGNUM *r, const BIGNUM *a, int n)

{

    int ret = 0;

    if (n < 0) {

        ERR_raise(ERR_LIB_BN, BN_R_INVALID_SHIFT);

        return 0;

    }

    bn_check_top(r);

    bn_check_top(a);

    ret = bn_rshift_fixed_top(r, a, n);

    bn_correct_top(r);

    bn_check_top(r);

    return ret;

}

/*

 * In respect to shift factor the execution time is invariant of

 * |n % BN_BITS2|, but not |n / BN_BITS2|. Or in other words pre-condition

 * for constant-time-ness for sufficiently[!] zero-padded inputs is

 * |n < BN_BITS2| or |n / BN_BITS2| being non-secret.

 */

int bn_rshift_fixed_top(BIGNUM *r, const BIGNUM *a, int n)

{

    int i, top, nw;

    unsigned int lb, rb;

    BN_ULONG *t, *f;

    BN_ULONG l, m, mask;

    assert(n >= 0);

    nw = n / BN_BITS2;

    if (nw >= a->top) {

        /* shouldn't happen, but formally required */

        BN_zero(r);

        return 1;

    }

    rb = (unsigned int)n % BN_BITS2;

    lb = BN_BITS2 - rb;

    lb %= BN_BITS2; /* say no to undefined behaviour */

    mask = (BN_ULONG)0 - lb; /* mask = 0 - (lb != 0) */

    mask |= mask >> 8;

    top = a->top - nw;

    if (r != a && bn_wexpand(r, top) == NULL)

        return 0;

    t = &(r->d[0]);

    f = &(a->d[nw]);

    l = f[0];

    for (i = 0; i < top - 1; i++) {

        m = f[i + 1];

        t[i] = (l >> rb) | ((m << lb) & mask);

        l = m;

    }

    t[i] = l >> rb;

    r->neg = a->neg;

    r->top = top;

    r->flags |= BN_FLG_FIXED_TOP;

    return 1;

}