#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include <unistd.h>
#include <string.h>

bool is_int_positive( int test_int ){
	/*
		multiply test_int by 2 to get the amount of characters/bits
		that would be in the hexadecimal value.
		For example:
		8-bit unsigned/signed = 1 * 2 = 2 (0x00 - 0xFF)
		16-bit unsigned/signed = 2 * 2 = 4 (0x0000 - 0xFFFF)
		32-bit unsigned/signed = 4 * 2 = 8 (0x00000000 - 0xFFFFFFFF)
		64-bit unsigned/signed = 8 * 2 = 16 (0x0000000000000000 - 0xFFFFFFFFFFFFFFFF)
	*/
	size_t value_bits = sizeof(test_int) * 2;
	/*
		Next check if first bit is 1 (positive integer) or 0 (negative integer).
		To do this the value bits must be used to right shift by the value bits count
		so only the MSB is left.
	*/
	size_t value_bits_shift = test_int >> (value_bits - 1);
	/*
		Now do bitwise and operation to compare if the MSB is 1 (negative) or 0 (positive).
		This works because the MSB tells if the integer contained in following bits should be taken
		as positive or negative integer.
		For positive integers the MSB is 0 and for negative integers the MSB is set to 1.
		Because value_bits_shift was shifted right by value_bits minus 1 the result is
		being left with just the bit containing the MSB value.
		The bitwise and below checks if the MSB is not 1 then return true (positive integer) and otherwise false (negative integer).
	*/
	return (!(value_bits_shift & 0x1)) ? true : false;
}

int main( int argc, char **args ){
	// Positive integer
	int first_int = 12345;
	// Negative integer
	int second_int = -12345;
	// Third integer that is just under 0
	int third_int = -1;
	// Fourth integer to test
	int fourth_int = 1;
	// Check the first integer
	fprintf( stdout, "Result for positive integer: %i\n", is_int_positive(first_int) );
	// Now do the same for the second one
	fprintf( stdout, "Result for negative integer: %i\n", is_int_positive(second_int) );
	// Third integer
	fprintf( stdout, "Result for third integer that is -1: %i\n", is_int_positive(third_int) );
	// Fourth integer
	fprintf( stdout, "Result for fourth integer that is just positive by one: %i\n", is_int_positive(fourth_int) );
	exit( EXIT_SUCCESS );
}