static int bnrand(int pseudorand, BIGNUM *rnd, int bits, int top, int bottom)
{
    unsigned char *buf = NULL;
    int ret = 0, bit, bytes, mask;
    time_t tim;

    if (bits < 0 || (bits == 1 && top > 0)) {
        BNerr(BN_F_BNRAND, BN_R_BITS_TOO_SMALL);
        return 0;
    }

    if (bits == 0) {
        BN_zero(rnd);
        return 1;
    }

    bytes = (bits + 7) / 8;
    bit = (bits - 1) % 8;
    mask = 0xff << (bit + 1);

    buf = OPENSSL_malloc(bytes);
    if (buf == NULL) {
        BNerr(BN_F_BNRAND, ERR_R_MALLOC_FAILURE);
        goto err;
    }

    /* make a random number and set the top and bottom bits */
    time(&tim);
    RAND_add(&tim, sizeof(tim), 0.0);

    if (RAND_bytes(buf, bytes) <= 0)
        goto err;

    if (pseudorand == 2) {
        /*
         * generate patterns that are more likely to trigger BN library bugs
         */
        int i;
        unsigned char c;

        for (i = 0; i < bytes; i++) {
            if (RAND_bytes(&c, 1) <= 0)
                goto err;
            if (c >= 128 && i > 0)
                buf[i] = buf[i - 1];
            else if (c < 42)
                buf[i] = 0;
            else if (c < 84)
                buf[i] = 255;
        }
    }

    if (top >= 0) {
        if (top) {
            if (bit == 0) {
                buf[0] = 1;
                buf[1] |= 0x80;
            } else {
                buf[0] |= (3 << (bit - 1));
            }
        } else {
            buf[0] |= (1 << bit);
        }
    }
    buf[0] &= ~mask;
    if (bottom)                 /* set bottom bit if requested */
        buf[bytes - 1] |= 1;
    if (!BN_bin2bn(buf, bytes, rnd))
        goto err;
    ret = 1;
 err:
    OPENSSL_clear_free(buf, bytes);
    bn_check_top(rnd);
    return (ret);
}