C binary AND, OR operators play with 32bit int

binary_operators.c

// gcc -o demo main.c -Wall

#include <stdio.h>

typedef unsigned int uint32_t;

/*
   ddacacba
&: 00ACACBA
|: DDFFFFFF
*/

static uint32_t mix_color(const uint32_t bg, const uint32_t fg)
{
    uint32_t a = fg >>24;
    if(a == 0) return bg;

    uint32_t rb = (((fg & 0x00FF00FF) * a) + ((bg & 0x00FF00FF) * (255 - a))) & 0xFF00FF00;
    uint32_t g  = (((fg & 0x0000FF00) * a) + ((bg & 0x0000FF00) * (255 - a))) & 0x00FF0000;
    uint32_t Fg = a + ((bg >>24) * (255 - a) / 255);

    return (Fg <<24) | ((rb | g) >>8);
}

int main()
{
  while(1)
  {
    uint32_t color = 0;
    fscanf(stdin, "%8x", &color);     // 11223344
    
    printf(" : %.8X\n", color <<24);  // 44000000

    printf(" : %.8X\n", color <<24 | (color & 0x00FFFFFF));  // 44223344
    // 44000000 | 00223344 = 44223344
    
                              //0xAARRGGBB
    printf("&: %.8X\n", color & 0x00FFFFFF);  // goes A to 00, rest untouched
    printf("|: %.8X\n", color | 0x00FFFFFF);  // leave A untouched, RGB to FF

    unsigned char i, *p = (unsigned char*)&color;
    for(i = 0; i < 4; i++)
    {
      printf("%d: %.2x %p \n", i, *p, p);
      p++;
    } puts("");
    /* 
      00998877 on LE have:
      0: 77 0x7ffeae5d2a14 
      1: 88 0x7ffeae5d2a15 
      2: 99 0x7ffeae5d2a16 
      3: 00 0x7ffeae5d2a17 
    */

    printf("m: %.8X\n", mix_color(0x00000000, color));
    puts("");
  }
  return 0;
}

./demo

00998877
: 77000000
: 77998877
&: 00998877
|: 00FFFFFF
0: 77 0x7ffeae5d2a14
1: 88 0x7ffeae5d2a15
2: 99 0x7ffeae5d2a16
3: 00 0x7ffeae5d2a17

m: 00000000

11998877
: 77000000
: 77998877
&: 00998877
|: 11FFFFFF
0: 77 0x7ffeae5d2a14
1: 88 0x7ffeae5d2a15
2: 99 0x7ffeae5d2a16
3: 11 0x7ffeae5d2a17

m: 110A0907