Language: C
Label: vulnerable
CWE: CWE-190 \u2014 Integer Overflow or Wraparound
The product performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control.

Code:
void bn_write_str(char *str, int len, const bn_t a, int radix) {
	bn_t t;
	dig_t d;
	int digits, l, i, j;
	char c;

	bn_null(t);

	l = bn_size_str(a, radix);
	if (len < l) {
		RLC_THROW(ERR_NO_BUFFER);
		return;
	}

	if (radix < 2 || radix > 64) {
		RLC_THROW(ERR_NO_VALID);
		return;
	}

	if (bn_is_zero(a) == 1) {
		*str++ = '0';
		*str = '\0';
		return;
	}

	RLC_TRY {
		bn_new(t);
		bn_copy(t, a);

		j = 0;
		if (t->sign == RLC_NEG) {
			str[j] = '-';
			j++;
			t->sign = RLC_POS;
		}

		digits = 0;
		while (!bn_is_zero(t) && j < len) {
			bn_div_rem_dig(t, &d, t, (dig_t)radix);
			str[j] = util_conv_char(d);
			digits++;
			j++;
		}

		/* Reverse the digits of the string. */
		i = 0;
		if (str[0] == '-') {
			i = 1;
		}

		j = l - 2;
		while (i < j) {
			c = str[i];
			str[i] = str[j];
			str[j] = c;
			++i;
			--j;
		}

		str[l - 1] = '\0';
	}
	RLC_CATCH_ANY {
		RLC_THROW(ERR_CAUGHT);
	}
	RLC_FINALLY {
		bn_free(t);
	}
}