/*

 * Copyright 1995-2023 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"

void BN_RECP_CTX_init(BN_RECP_CTX *recp)

{

    memset(recp, 0, sizeof(*recp));

    bn_init(&(recp->N));

    bn_init(&(recp->Nr));

}

BN_RECP_CTX *BN_RECP_CTX_new(void)

{

    BN_RECP_CTX *ret;

    if ((ret = OPENSSL_zalloc(sizeof(*ret))) == NULL)

        return NULL;

    bn_init(&(ret->N));

    bn_init(&(ret->Nr));

    ret->flags = BN_FLG_MALLOCED;

    return ret;

}

void BN_RECP_CTX_free(BN_RECP_CTX *recp)

{

    if (recp == NULL)

        return;

    BN_free(&recp->N);

    BN_free(&recp->Nr);

    if (recp->flags & BN_FLG_MALLOCED)

        OPENSSL_free(recp);

}

int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *d, BN_CTX *ctx)

{

    if (BN_is_zero(d) || !BN_copy(&(recp->N), d))

        return 0;

    BN_zero(&(recp->Nr));

    recp->num_bits = BN_num_bits(d);

    recp->shift = 0;

    return 1;

}

int BN_mod_mul_reciprocal(BIGNUM *r, const BIGNUM *x, const BIGNUM *y,

    BN_RECP_CTX *recp, BN_CTX *ctx)

{

    int ret = 0;

    BIGNUM *a;

    const BIGNUM *ca;

    BN_CTX_start(ctx);

    if ((a = BN_CTX_get(ctx)) == NULL)

        goto err;

    if (y != NULL) {

        if (x == y) {

            if (!BN_sqr(a, x, ctx))

                goto err;

        } else {

            if (!BN_mul(a, x, y, ctx))

                goto err;

        }

        ca = a;

    } else

        ca = x; /* Just do the mod */

    ret = BN_div_recp(NULL, r, ca, recp, ctx);

err:

    BN_CTX_end(ctx);

    bn_check_top(r);

    return ret;

}

int BN_div_recp(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m,

    BN_RECP_CTX *recp, BN_CTX *ctx)

{

    int i, j, ret = 0;

    BIGNUM *a, *b, *d, *r;

    BN_CTX_start(ctx);

    d = (dv != NULL) ? dv : BN_CTX_get(ctx);

    r = (rem != NULL) ? rem : BN_CTX_get(ctx);

    a = BN_CTX_get(ctx);

    b = BN_CTX_get(ctx);

    if (b == NULL)

        goto err;

    if (BN_ucmp(m, &(recp->N)) < 0) {

        BN_zero(d);

        if (!BN_copy(r, m)) {

            BN_CTX_end(ctx);

            return 0;

        }

        BN_CTX_end(ctx);

        return 1;

    }

    /*

     * We want the remainder Given input of ABCDEF / ab we need multiply

     * ABCDEF by 3 digests of the reciprocal of ab

     */

    /* i := max(BN_num_bits(m), 2*BN_num_bits(N)) */

    i = BN_num_bits(m);

    j = recp->num_bits << 1;

    if (j > i)

        i = j;

    /* Nr := round(2^i / N) */

    if (i != recp->shift)

        recp->shift = BN_reciprocal(&(recp->Nr), &(recp->N), i, ctx);

    /* BN_reciprocal could have returned -1 for an error */

    if (recp->shift == -1)

        goto err;

    /*-

     * d := |round(round(m / 2^BN_num_bits(N)) * recp->Nr / 2^(i - BN_num_bits(N)))|

     *    = |round(round(m / 2^BN_num_bits(N)) * round(2^i / N) / 2^(i - BN_num_bits(N)))|

     *   <= |(m / 2^BN_num_bits(N)) * (2^i / N) * (2^BN_num_bits(N) / 2^i)|

     *    = |m/N|

     */

    if (!BN_rshift(a, m, recp->num_bits))

        goto err;

    if (!BN_mul(b, a, &(recp->Nr), ctx))

        goto err;

    if (!BN_rshift(d, b, i - recp->num_bits))

        goto err;

    d->neg = 0;

    if (!BN_mul(b, &(recp->N), d, ctx))

        goto err;

    if (!BN_usub(r, m, b))

        goto err;

    r->neg = 0;

    j = 0;

    while (BN_ucmp(r, &(recp->N)) >= 0) {

        if (j++ > 2) {

            ERR_raise(ERR_LIB_BN, BN_R_BAD_RECIPROCAL);

            goto err;

        }

        if (!BN_usub(r, r, &(recp->N)))

            goto err;

        if (!BN_add_word(d, 1))

            goto err;

    }

    r->neg = BN_is_zero(r) ? 0 : m->neg;

    d->neg = m->neg ^ recp->N.neg;

    ret = 1;

err:

    BN_CTX_end(ctx);

    bn_check_top(dv);

    bn_check_top(rem);

    return ret;

}

/*

 * len is the expected size of the result We actually calculate with an extra

 * word of precision, so we can do faster division if the remainder is not

 * required.

 */

/* r := 2^len / m */

int BN_reciprocal(BIGNUM *r, const BIGNUM *m, int len, BN_CTX *ctx)

{

    int ret = -1;

    BIGNUM *t;

    BN_CTX_start(ctx);

    if ((t = BN_CTX_get(ctx)) == NULL)

        goto err;

    if (!BN_set_bit(t, len))

        goto err;

    if (!BN_div(r, NULL, t, m, ctx))

        goto err;

    ret = len;

err:

    bn_check_top(r);

    BN_CTX_end(ctx);

    return ret;

}