#include <stdio.h>
#include <stdint.h>

#define HALFBYTE_SIZE   (4)
#define HALFBYTE_MASK   (0xF)
#define HALFBYTE_R      (HALFBYTE_MASK << HALFBYTE_SIZE)
#define HALFBYTE_L      (HALFBYTE_MASK)
static int test_counter;
/*
 * if position is st to 0, then change only first halfbyte (range from 0 to 3),
 * otherwise if position is se to 1, change only second halfbyte (range from 4 to 7)
 */

uint8_t halfByteStorage(uint8_t byte, uint8_t position, uint8_t value)
{
    if(position)
    {
        return ((byte & HALFBYTE_L) | value << HALFBYTE_SIZE);
    }

    else
    {
        return ((byte & HALFBYTE_R) | value);
    }
}

/*
 * assertP:
 * function is made for easy module tests of halfByteStorage function.
 * INPUT:
 * byte: storage for two halfbytes
 * position: position of halfbyte to change
 * value: new value to store
 * value: expected result of halfByteStorage() function
 * OUTPUT:
 * printed result of the test
 */
void assertP(uint8_t byte, uint8_t position, uint8_t value, uint8_t expected)
{
    ++test_counter;
    uint8_t ret = 0;
    ret = halfByteStorage(byte, position, value);

    if(ret == expected)
        printf("test %d passed\n", test_counter);

    else
        printf("test %d fails\n", test_counter);
}

int main()
{

    //test first halfbyte
    assertP(0xAA, 0, 5, 165); // halfbyte, position, value, expected
    assertP(0xAA, 0, 7, 167);
    assertP(0xFF, 0, 5, 245);
    assertP(0xFF, 0, 0, 240);

    //test second halfbyte
    assertP(0xAA, 1, 5, 90); // halfbyte, position, value, expected
    assertP(0xAA, 1, 7, 122);
    assertP(0xFF, 1, 5, 95);
    assertP(0xFF, 1, 0, 15);

    //test random values (should not pass tests)
    assertP(0xAA, 1, 4, 10); // halfbyte, position, value, expected
    assertP(0xAA, 0, 7, 99);
    assertP(0xFF, 1, 6, 12);
    assertP(0xFF, 0, 8, 55);
    return 0;
}