calculation for absolute value.

abs.c

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

int main(void)
{
        uint8_t u;
        int8_t s;
        uint32_t i;

        printf("step    u       s\n");
        for (i = 0, u = 0, s = INT8_MIN; i <= 255; ++i, ++u, ++s) {
                int8_t t = u;
                int8_t m_u = 0x80;
                int8_t m_s = 0x00;
                printf("%02d: %d %d\n", i, abs(t ^ m_u), abs(s ^ m_s));
        }

        return EXIT_SUCCESS;
}