/*

 * 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;

}