C++ integer parser (based on JVM sources)

ParseUtils.cpp

#include <climits>
#include <cstring>

#define MIN_RADIX 2
#define MAX_RADIX 36

int digitVal(char ch, int radix) {
	if (radix < MIN_RADIX || radix > MAX_RADIX)
		return -1;
	if (ch >= 'A' && ch <= 'Z' && ch < radix + 'A' - 10)
		return ch - 'A' + 10;
	if (ch >= 'a' && ch <= 'z' && ch < radix + 'a' - 10)
		return ch - 'a' + 10;
	if (ch >= '0' && ch <= '9' && ch < radix + '0')
		return ch - '0';
	return -1;
}

bool tryParseInt(const char *s, int radix, int *resultPtr) {
	if (s == nullptr || radix < MIN_RADIX || radix > MAX_RADIX)
		return false;

	size_t len = strlen(s);
	if (len > 0) {
		int result = 0;
		bool negative = false;
		int limit = -INT_MAX;
		int index = 0;

		char firstChar = s[0];
		if (firstChar < '0') { // Possible leading "+" or "-"
			if (firstChar == '-') {
				negative = true;
				limit = INT_MIN;
			} else if (firstChar != '+')
				return false;

			if (len == 1) // Cannot have lone "+" or "-"
				return false;
			index++;
		}

		int multmin = limit / radix;
		while (index < len) {
			// Accumulating negatively avoids surprises near MAX_VALUE
			int digit = digitVal(s[index++], radix);
			if (digit < 0)
				return false;
			if (result < multmin)
				return false;
			result *= radix;
			if (result < limit + digit)
				return false;
			result -= digit;
		}

		*resultPtr = negative ? result : -result;
		return true;
	}

	return false;
}

bool tryParseInt(const char *s, int *resultPtr) {
	return tryParseInt(s, 10, resultPtr);
}

int parseInt(const char *s, int radix) {
	int i;
	return tryParseInt(s, radix, &i) ? i : 0;
}

int parseInt(const char *s) {
	int i;
	return tryParseInt(s, &i) ? i : 0;
}

ParseUtils.h

#pragma once

bool tryParseInt(const char *s, int radix, int *resultPtr);

bool tryParseInt(const char *s, int *resultPtr);

int parseInt(const char *s, int radix);

int parseInt(const char *s);