static int bn_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont)
{
    BIGNUM *n;
    BN_ULONG *ap, *np, *rp, n0, v, carry;
    int nl, max, i;
    unsigned int rtop;
    n = &(mont->N);
    nl = n->top;
    if (nl == 0) {
        ret->top = 0;
        return 1;
    }
    max = (2 * nl);
    if (bn_wexpand(r, max) == NULL)
        return 0;
    r->neg ^= n->neg;
    np = n->d;
    rp = r->d;
    for (rtop = r->top, i = 0; i < max; i++) {
        v = (BN_ULONG)0 - ((i - rtop) >> (8 * sizeof(rtop) - 1));
        rp[i] &= v;
    }
    r->top = max;
    r->flags |= BN_FLG_FIXED_TOP;
    n0 = mont->n0[0];
    for (carry = 0, i = 0; i < nl; i++, rp++) {
        v = bn_mul_add_words(rp, np, nl, (rp[0] * n0) & BN_MASK2);
        v = (v + carry + rp[nl]) & BN_MASK2;
        carry |= (v != rp[nl]);
        carry &= (v <= rp[nl]);
        rp[nl] = v;
    }
    if (bn_wexpand(ret, nl) == NULL)
        return 0;
    ret->top = nl;
    ret->flags |= BN_FLG_FIXED_TOP;
    ret->neg = r->neg;
    rp = ret->d;
    ap = &(r->d[nl]);
    carry -= bn_sub_words(rp, ap, np, nl);
    for (i = 0; i < nl; i++) {
        rp[i] = (carry & ap[i]) | (~carry & rp[i]);
        ap[i] = 0;
    }
    return 1;
}
['int bn_mul_mont_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,\n                          BN_MONT_CTX *mont, BN_CTX *ctx)\n{\n    BIGNUM *tmp;\n    int ret = 0;\n    int num = mont->N.top;\n#if defined(OPENSSL_BN_ASM_MONT) && defined(MONT_WORD)\n    if (num > 1 && a->top == num && b->top == num) {\n        if (bn_wexpand(r, num) == NULL)\n            return 0;\n        if (bn_mul_mont(r->d, a->d, b->d, mont->N.d, mont->n0, num)) {\n            r->neg = a->neg ^ b->neg;\n            r->top = num;\n            r->flags |= BN_FLG_FIXED_TOP;\n            return 1;\n        }\n    }\n#endif\n    if ((a->top + b->top) > 2 * num)\n        return 0;\n    BN_CTX_start(ctx);\n    tmp = BN_CTX_get(ctx);\n    if (tmp == NULL)\n        goto err;\n    bn_check_top(tmp);\n    if (a == b) {\n        if (!bn_sqr_fixed_top(tmp, a, ctx))\n            goto err;\n    } else {\n        if (!bn_mul_fixed_top(tmp, a, b, ctx))\n            goto err;\n    }\n#ifdef MONT_WORD\n    if (!bn_from_montgomery_word(r, tmp, mont))\n        goto err;\n#else\n    if (!BN_from_montgomery(r, tmp, mont, ctx))\n        goto err;\n#endif\n    ret = 1;\n err:\n    BN_CTX_end(ctx);\n    return ret;\n}', 'static int bn_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont)\n{\n    BIGNUM *n;\n    BN_ULONG *ap, *np, *rp, n0, v, carry;\n    int nl, max, i;\n    unsigned int rtop;\n    n = &(mont->N);\n    nl = n->top;\n    if (nl == 0) {\n        ret->top = 0;\n        return 1;\n    }\n    max = (2 * nl);\n    if (bn_wexpand(r, max) == NULL)\n        return 0;\n    r->neg ^= n->neg;\n    np = n->d;\n    rp = r->d;\n    for (rtop = r->top, i = 0; i < max; i++) {\n        v = (BN_ULONG)0 - ((i - rtop) >> (8 * sizeof(rtop) - 1));\n        rp[i] &= v;\n    }\n    r->top = max;\n    r->flags |= BN_FLG_FIXED_TOP;\n    n0 = mont->n0[0];\n    for (carry = 0, i = 0; i < nl; i++, rp++) {\n        v = bn_mul_add_words(rp, np, nl, (rp[0] * n0) & BN_MASK2);\n        v = (v + carry + rp[nl]) & BN_MASK2;\n        carry |= (v != rp[nl]);\n        carry &= (v <= rp[nl]);\n        rp[nl] = v;\n    }\n    if (bn_wexpand(ret, nl) == NULL)\n        return 0;\n    ret->top = nl;\n    ret->flags |= BN_FLG_FIXED_TOP;\n    ret->neg = r->neg;\n    rp = ret->d;\n    ap = &(r->d[nl]);\n    carry -= bn_sub_words(rp, ap, np, nl);\n    for (i = 0; i < nl; i++) {\n        rp[i] = (carry & ap[i]) | (~carry & rp[i]);\n        ap[i] = 0;\n    }\n    return 1;\n}', 'BIGNUM *bn_wexpand(BIGNUM *a, int words)\n{\n    return (words <= a->dmax) ? a : bn_expand2(a, words);\n}']