/*

 * Copyright 1995-2026 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"

/* r must not be a */

/*

 * I've just gone over this and it is now %20 faster on x86 - eay - 27 Jun 96

 */

int BN_sqr(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)

{

    int ret = bn_sqr_fixed_top(r, a, ctx);

    bn_correct_top(r);

    bn_check_top(r);

    return ret;

}

int bn_sqr_fixed_top(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)

{

    int max, al;

    int ret = 0;

    BIGNUM *tmp, *rr;

    bn_check_top(a);

    al = a->top;

    if (al <= 0) {

        r->top = 0;

        r->neg = 0;

        return 1;

    }

    BN_CTX_start(ctx);

    rr = (a != r) ? r : BN_CTX_get(ctx);

    tmp = BN_CTX_get(ctx);

    if (rr == NULL || tmp == NULL)

        goto err;

    max = 2 * al; /* Non-zero (from above) */

    if (bn_wexpand(rr, max) == NULL)

        goto err;

    if (al == 4) {

#ifdef OPENSSL_SMALL_FOOTPRINT

        BN_ULONG t[8];

        bn_sqr_normal(rr->d, a->d, 4, t);

#else

        bn_sqr_comba4(rr->d, a->d);

#endif

    } else if (al == 8) {

#ifdef OPENSSL_SMALL_FOOTPRINT

        BN_ULONG t[16];

        bn_sqr_normal(rr->d, a->d, 8, t);

#else

        bn_sqr_comba8(rr->d, a->d);

#endif

    } else {

#ifdef OPENSSL_SMALL_FOOTPRINT

        if (bn_wexpand(tmp, max) == NULL)

            goto err;

        bn_sqr_normal(rr->d, a->d, al, tmp->d);

#else

        if (al < BN_SQR_RECURSIVE_SIZE_NORMAL) {

            BN_ULONG t[BN_SQR_RECURSIVE_SIZE_NORMAL * 2];

            bn_sqr_normal(rr->d, a->d, al, t);

        } else {

            int j, k;

            j = BN_num_bits_word((BN_ULONG)al);

            j = 1 << (j - 1);

            k = j + j;

            if (al == j) {

                if (bn_wexpand(tmp, k * 2) == NULL)

                    goto err;

                bn_sqr_recursive(rr->d, a->d, al, tmp->d);

            } else {

                if (bn_wexpand(tmp, max) == NULL)

                    goto err;

                bn_sqr_normal(rr->d, a->d, al, tmp->d);

            }

        }

#endif

    }

    rr->neg = 0;

    rr->top = max;

    rr->flags |= BN_FLG_FIXED_TOP;

    if (r != rr && BN_copy(r, rr) == NULL)

        goto err;

    ret = 1;

err:

    bn_check_top(rr);

    bn_check_top(tmp);

    BN_CTX_end(ctx);

    return ret;

}

/* tmp must have 2*n words */

void bn_sqr_normal(BN_ULONG *r, const BN_ULONG *a, int n, BN_ULONG *tmp)

{

    int i, j, max;

    const BN_ULONG *ap;

    BN_ULONG *rp;

    max = n * 2;

    ap = a;

    rp = r;

    rp[0] = rp[max - 1] = 0;

    rp++;

    j = n;

    if (--j > 0) {

        ap++;

        rp[j] = bn_mul_words(rp, ap, j, ap[-1]);

        rp += 2;

    }

    for (i = n - 2; i > 0; i--) {

        j--;

        ap++;

        rp[j] = bn_mul_add_words(rp, ap, j, ap[-1]);

        rp += 2;

    }

    bn_add_words(r, r, r, max);

    /* There will not be a carry */

    bn_sqr_words(tmp, a, n);

    bn_add_words(r, r, tmp, max);

}

#ifndef OPENSSL_SMALL_FOOTPRINT

/*-

 * r is 2*n words in size,

 * a and b are both n words in size.    (There's not actually a 'b' here ...)

 * n must be a power of 2.

 * We multiply and return the result.

 * t must be 2*n words in size

 * We calculate

 * a[0]*b[0]

 * a[0]*b[0]+a[1]*b[1]+(a[0]-a[1])*(b[1]-b[0])

 * a[1]*b[1]

 */

void bn_sqr_recursive(BN_ULONG *r, const BN_ULONG *a, int n2, BN_ULONG *t)

{

    int n = n2 / 2;

    int zero, c1;

    BN_ULONG ln, lo, *p;

    if (n2 == 4) {

        bn_sqr_comba4(r, a);

        return;

    } else if (n2 == 8) {

        bn_sqr_comba8(r, a);

        return;

    }

    if (n2 < BN_SQR_RECURSIVE_SIZE_NORMAL) {

        bn_sqr_normal(r, a, n2, t);

        return;

    }

    /* r=(a[0]-a[1])*(a[1]-a[0]) */

    c1 = bn_cmp_words(a, &(a[n]), n);

    zero = 0;

    if (c1 > 0)

        bn_sub_words(t, a, &(a[n]), n);

    else if (c1 < 0)

        bn_sub_words(t, &(a[n]), a, n);

    else

        zero = 1;

    /* The result will always be negative unless it is zero */

    p = &(t[n2 * 2]);

    if (!zero)

        bn_sqr_recursive(&(t[n2]), t, n, p);

    else

        memset(&t[n2], 0, sizeof(*t) * n2);

    bn_sqr_recursive(r, a, n, p);

    bn_sqr_recursive(&(r[n2]), &(a[n]), n, p);

    /*-

     * t[32] holds (a[0]-a[1])*(a[1]-a[0]), it is negative or zero

     * r[10] holds (a[0]*b[0])

     * r[32] holds (b[1]*b[1])

     */

    c1 = (int)(bn_add_words(t, r, &(r[n2]), n2));

    /* t[32] is negative */

    c1 -= (int)(bn_sub_words(&(t[n2]), t, &(t[n2]), n2));

    /*-

     * t[32] holds (a[0]-a[1])*(a[1]-a[0])+(a[0]*a[0])+(a[1]*a[1])

     * r[10] holds (a[0]*a[0])

     * r[32] holds (a[1]*a[1])

     * c1 holds the carry bits

     */

    c1 += (int)(bn_add_words(&(r[n]), &(r[n]), &(t[n2]), n2));

    if (c1) {

        p = &(r[n + n2]);

        lo = *p;

        ln = (lo + c1) & BN_MASK2;

        *p = ln;

        /*

         * The overflow will stop before we over write words we should not

         * overwrite

         */

        if (ln < (BN_ULONG)c1) {

            do {

                p++;

                lo = *p;

                ln = (lo + 1) & BN_MASK2;

                *p = ln;

            } while (ln == 0);

        }

    }

}

#endif