#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>

typedef unsigned char uchar;

uchar get_bit(uchar ch, int bit_idx) {
    return ch >> (7 - bit_idx) & 1;
}

uchar set_bit(uchar ch, int bit_idx, uchar new_value) {
    if(new_value) {                         //                                   bit_idx==2
        // Set bit (to 1)                   //                                      ↓
        return ch | (1 << (7 - bit_idx));   // bitwise-or with a byte like this:  00100000
    }
    else {
        // Unset bit (to 0)                   //                                    bit_idx==2
        assert(new_value == 0);               //                                       ↓
        return ch & (~ (1 << (7 - bit_idx))); // bitwise-and with a byte like this:  11011111
    }
}

// NAÏVE way
uchar get_bits(uchar ch, int start_bit_idx, int end_bit_idx) {  // end_bit_idx is inclusive
    // Bits from the source byte ('ch') will be in the least signficant side of the result.
    //  - least-significant means the right side, i.e., the side that affects the magnitude least.
    uchar result = 0x00; // hex for 0 == 00000000₂
    int num_bits_to_get = end_bit_idx - start_bit_idx + 1;
    int result_start_bit_idx = 8 - num_bits_to_get;
    for(int src_idx = start_bit_idx; src_idx <= end_bit_idx; src_idx++) {
        uchar bit = get_bit(ch, src_idx);
        assert(bit == 0 || bit == 1);
        uchar result_bit_idx = result_start_bit_idx + (src_idx - start_bit_idx);
        //uchar result_bit_idx = result_start_bit_idx + (start_bit_idx - src_idx);  // BUG!!!
        result = set_bit(result, result_bit_idx, bit);
    }
    return result;
}

int main(int argc, char* argv[]) {
    assert( get_bit(0xcb, 1) == 1 );
    assert( set_bit(0x00, 0, 1) == 0x80 ); // 10000000₂
    assert( set_bit(0xcb, 2, 1) == 0xeb ); // 0xcb == 11001011₂, 0xeb == 11101011₂
    assert( set_bit(0xeb, 2, 0) == 0xcb ); // 0xcb == 11001011₂, 0xeb == 11101011₂

    // assert( get_bits(10111100₂, 3, 6) == ₀₀₀₀1110₂)
    //                     ‾‾‾‾
    assert( get_bits(0xbc, 3, 6) == 0x0e);
    return EXIT_SUCCESS;
}
/* vim: set tabstop=4 shiftwidth=4 fileencoding=utf-8 noexpandtab: */