// BIT STUFFING in C and C++
//    Something that I should have mentioned on Tuesday

#include <stdio.h>

struct sexpression
{ unsigned int type: 3;    // range is 0 to 7
  unsigned int inuse: 1;   // only used during garbage collection
  int value: 28;           // range will only be +/- 134,000,000.
};

// the size of an sexpression object is only 4 bytes, whcih is
// nice and efficient on today's computers, but those 32 bits
// are divided up 3:1:28 amongst three components. All the packing
// and unpacking is done automatically for you, so you don't
// have to bother with all the fiddly shifting and bitwise anding.

void main()
{ printf("size = %d bytes\n", sizeof(sexpression));
  sexpression s;
  s.type = 5;
  s.value = 123456;
  printf("%d %d %d (5, ?, 123456)\n", s.type, s.inuse, s.value);
  s.value = 2000000000;
  printf("%d %d %d (5, ?, 2000000000)\n", s.type, s.inuse, s.value);
  s.type = 11;
  s.value = -5;
  printf("%d %d %d (11, ?, -5)\n", s.type, s.inuse, s.value);
  s.type = 3;
  s.inuse = 1;
  printf("%d %d %d (3, 1, -5)\n", s.type, s.inuse, s.value);
  s.inuse = 0;
  printf("%d %d %d (3, 0, -5)\n", s.type, s.inuse, s.value); }


/* this is the output produced

size = 4 bytes
5 0 123456 (5, ?, 123456)
5 0 120951808 (5, ?, 2000000000)
3 0 -5 (11, ?, -5)
3 1 -5 (3, 1, -5)
3 0 -5 (3, 0, -5)

*/