/* Provenance: openssl/openssl bn_sub_words (fixed).
 * repo: openssl/openssl
 * commit: a00d757d9ca212994625d1a02c81cc5edd27e13b
 * parent: 908eaceb62624f5b5c505b286d904bd3a4e8a64a
 * commit_url: https://github.com/openssl/openssl/commit/a00d757d9ca212994625d1a02c81cc5edd27e13b
 * cve: CVE-2022-4304
 * license: Apache-2.0
 * function: bn_sub_words
 * relpath: crypto/bn/bn_asm.c
 */

BN_ULONG bn_sub_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *b,
                      int n)
{
    BN_ULONG t1, t2;
    int c = 0;

    assert(n >= 0);
    if (n <= 0)
        return (BN_ULONG)0;

#ifndef OPENSSL_SMALL_FOOTPRINT
    while (n & ~3) {
        t1 = a[0];
        t2 = (t1 - c) & BN_MASK2;
        c  = (t2 > t1);
        t1 = b[0];
        t1 = (t2 - t1) & BN_MASK2;
        r[0] = t1;
        c += (t1 > t2);
        t1 = a[1];
        t2 = (t1 - c) & BN_MASK2;
        c  = (t2 > t1);
        t1 = b[1];
        t1 = (t2 - t1) & BN_MASK2;
        r[1] = t1;
        c += (t1 > t2);
        t1 = a[2];
        t2 = (t1 - c) & BN_MASK2;
        c  = (t2 > t1);
        t1 = b[2];
        t1 = (t2 - t1) & BN_MASK2;
        r[2] = t1;
        c += (t1 > t2);
        t1 = a[3];
        t2 = (t1 - c) & BN_MASK2;
        c  = (t2 > t1);
        t1 = b[3];
        t1 = (t2 - t1) & BN_MASK2;
        r[3] = t1;
        c += (t1 > t2);
        a += 4;
        b += 4;
        r += 4;
        n -= 4;
    }
#endif
    while (n) {
        t1 = a[0];
        t2 = (t1 - c) & BN_MASK2;
        c  = (t2 > t1);
        t1 = b[0];
        t1 = (t2 - t1) & BN_MASK2;
        r[0] = t1;
        c += (t1 > t2);
        a++;
        b++;
        r++;
        n--;
    }
    return c;
}