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char dec2hexChar(short int n) {
	if (0 <= n && n <= 9) {
		return char(short('0') + n);
	}
	else if (10 <= n && n <= 15) {
		return char(short('A') + n - 10);
	}
	else {
		return char(0);
	}
}

short int hexChar2dec(char c) {
	if ('0' <= c && c <= '9') {
		return short(c - '0');
	}
	else if ('a' <= c && c <= 'f') {
		return (short(c - 'a') + 10);
	}
	else if ('A' <= c && c <= 'F') {
		return (short(c - 'A') + 10);
	}
	else {
		return -1;
	}
}

std::string escapeURL(const std::string &URL)
{
	std::string result = "";
	for (unsigned int i = 0; i < URL.size(); i++) {
		char c = URL[i];
		if (
			(c >= 'a' && c <= 'z')
			|| (c >= 'A' && c <= 'Z')
			|| (c >= '0' && c <= '9')
			|| c == '!'
			|| (c >= '\'' && c <= '*')
			|| c == '-'
			|| c == '.'
			|| c == '_'
			|| c == '~') {
			result += c;
		}
		else {
			int j = (short int)c;
			if (j < 0) {
				j += 256;
			}
			int i1, i0;
			i1 = j / 16;
			i0 = j - i1 * 16;
			result += '%';
			result += dec2hexChar(i1);
			result += dec2hexChar(i0);
		}
	}
	return result;
}