/*
    bitwise.c
    Jeff Ondich, 9 Jan 2022

    Some bitwise logical operations (|, &, >>)
*/

#include <stdio.h>

void print_binary(int n, FILE *stream);

int main(int argc, char *argv[]) {
    // Experiment 1
    printf("===== 1. bitwise OR to turn a bit on =====\n");
    int a = 0x00000023;
    int bit = 0x00000080;
    int b = a | bit;
    printf("a=%d, bit=%d, b=%d\n", a, bit, b);
    printf("a   = ");
    print_binary(a, stdout);
    printf("\nbit = ");
    print_binary(bit, stdout);
    printf("\nb   = ");
    print_binary(b, stdout);
    printf("\n\n");

    // Experiment 2
    printf("===== 2. bitwise AND to turn a bit off =====\n");
    a = 0x00000023;
    int mask = 0xFFFFFFFD;
    b = a & mask;
    printf("a=%d, mask=%d, b=%d\n", a, mask, b);
    printf("a    = ");
    print_binary(a, stdout);
    printf("\nmask = ");
    print_binary(mask, stdout);
    printf("\nb    = ");
    print_binary(b, stdout);
    printf("\n\n");

    // Experiment 3
    printf("===== 3. bitwise AND to mask out all but lower-order byte =====\n");
    a = 0x1234ABCD;
    mask = 0x000000FF;
    b = a & mask;
    printf("a=%d, mask=%d, b=%d\n", a, mask, b);
    printf("a    = ");
    print_binary(a, stdout);
    printf("\nmask = ");
    print_binary(mask, stdout);
    printf("\nb    = ");
    print_binary(b, stdout);
    printf("\n\n");

    // Experiment 4
    printf("===== 4. bit shift to move middle bits to low-order bits =====\n");
    a = 0x1234ABCD;
    int shift = 8;
    b = a >> shift;
    printf("a=0x%X, shift=0x%X, b=0x%X\n", a, shift, b);
    printf("a     = ");
    print_binary(a, stdout);
    printf("\nshift = ");
    print_binary(shift, stdout);
    printf("\nb     = ");
    print_binary(b, stdout);
    printf("\n\n");

    // Experiment 5
    printf("===== 5. what if a is negative =====\n");
    a = 0x8765ABCD;
    shift = 8;
    b = a >> shift;
    printf("a=0x%X, shift=0x%X, b=0x%X\n", a, shift, b);
    printf("a     = ");
    print_binary(a, stdout);
    printf("\nshift = ");
    print_binary(shift, stdout);
    printf("\nb     = ");
    print_binary(b, stdout);
    printf("\n\n");

    // Experiment 6
    printf("===== 6. building a mask =====\n");
    a = 0x1234ABCD; // I want to zero out bits 8-11 (i.e. the B in that hexadecimal)
    int inverted_mask = 0x00000F00; // the bits I want to squash are the four bits (8-11) covered by the F
    mask = ~inverted_mask; // this bitwise NOT converts 0x0000F000 to 0xFFFF0FFF
    printf("a=0x%X, inverted_mask=0x%X, mask=0x%X\n", a, inverted_mask, mask);
    printf("a & mask: 0x%X\n", a & mask);
    printf("\n\n");

    return 0;
}

void print_binary(int n, FILE *stream) {
    int bits_printed = 0;
    for (unsigned int k = 0x80000000; k != 0; k = (k >> 1)) {
        char bit = (k & n) != 0 ? '1' : '0';
        fputc(bit, stream);
        bits_printed++;
        if ((bits_printed % 4) == 0) {
            fputc(' ', stream);
        }
    }
}