int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
{
    int max, min, dif;
    BN_ULONG t1, t2, borrow, *rp;
    const BN_ULONG *ap, *bp;
    bn_check_top(a);
    bn_check_top(b);
    max = a->top;
    min = b->top;
    dif = max - min;
    if (dif < 0) {
        BNerr(BN_F_BN_USUB, BN_R_ARG2_LT_ARG3);
        return 0;
    }
    if (bn_wexpand(r, max) == NULL)
        return 0;
    ap = a->d;
    bp = b->d;
    rp = r->d;
    borrow = bn_sub_words(rp, ap, bp, min);
    ap += min;
    rp += min;
    while (dif) {
        dif--;
        t1 = *(ap++);
        t2 = (t1 - borrow) & BN_MASK2;
        *(rp++) = t2;
        borrow &= (t1 == 0);
    }
    while (max && *--rp == 0)
        max--;
    r->top = max;
    r->neg = 0;
    bn_pollute(r);
    return 1;
}
['static int test_check_public_exponent(void)\n{\n    int ret = 0;\n    BIGNUM *e = NULL;\n    ret = TEST_ptr(e = BN_new())\n          && TEST_true(BN_set_word(e, 65535))\n          && TEST_false(rsa_check_public_exponent(e))\n          && TEST_true(BN_set_word(e, 65536))\n          && TEST_false(rsa_check_public_exponent(e))\n          && TEST_true(BN_set_word(e, 65537))\n          && TEST_true(rsa_check_public_exponent(e))\n          && TEST_true(BN_lshift(e, BN_value_one(), 256))\n          && TEST_false(rsa_check_public_exponent(e))\n          && TEST_true(BN_sub(e, e, BN_value_one()))\n          && TEST_true(rsa_check_public_exponent(e));\n    BN_free(e);\n    return ret;\n}', 'const BIGNUM *BN_value_one(void)\n{\n    static const BN_ULONG data_one = 1L;\n    static const BIGNUM const_one =\n        { (BN_ULONG *)&data_one, 1, 1, 0, BN_FLG_STATIC_DATA };\n    return &const_one;\n}', 'int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)\n{\n    int ret, r_neg, cmp_res;\n    bn_check_top(a);\n    bn_check_top(b);\n    if (a->neg != b->neg) {\n        r_neg = a->neg;\n        ret = BN_uadd(r, a, b);\n    } else {\n        cmp_res = BN_ucmp(a, b);\n        if (cmp_res > 0) {\n            r_neg = a->neg;\n            ret = BN_usub(r, a, b);\n        } else if (cmp_res < 0) {\n            r_neg = !b->neg;\n            ret = BN_usub(r, b, a);\n        } else {\n            r_neg = 0;\n            BN_zero(r);\n            ret = 1;\n        }\n    }\n    r->neg = r_neg;\n    bn_check_top(r);\n    return ret;\n}', 'int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)\n{\n    int max, min, dif;\n    BN_ULONG t1, t2, borrow, *rp;\n    const BN_ULONG *ap, *bp;\n    bn_check_top(a);\n    bn_check_top(b);\n    max = a->top;\n    min = b->top;\n    dif = max - min;\n    if (dif < 0) {\n        BNerr(BN_F_BN_USUB, BN_R_ARG2_LT_ARG3);\n        return 0;\n    }\n    if (bn_wexpand(r, max) == NULL)\n        return 0;\n    ap = a->d;\n    bp = b->d;\n    rp = r->d;\n    borrow = bn_sub_words(rp, ap, bp, min);\n    ap += min;\n    rp += min;\n    while (dif) {\n        dif--;\n        t1 = *(ap++);\n        t2 = (t1 - borrow) & BN_MASK2;\n        *(rp++) = t2;\n        borrow &= (t1 == 0);\n    }\n    while (max && *--rp == 0)\n        max--;\n    r->top = max;\n    r->neg = 0;\n    bn_pollute(r);\n    return 1;\n}']