C language source code fragment bit operation

The following code segment is the code bit operation on the C language fragments.

  Copyright 2011 Shao-Chuan Wang <shaochuan.wang AT gmail.com>

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

typedef struct {
  int size;
} packed_bits;

#define INT_MAX_BIT_MASK (1 << (INT_NBITS-1))

{
  if (!b_array)
    return NULL;
  p = malloc(sizeof(packed_bits));
  if (!p) {
    free(b_array);
    return NULL;
  }
  p->size = n_int;
  p->b = b_array;
  return p;
}

{
  int i;
  if (!p)
    return -1;
  b = p->b;
  for (i = p->size-1;i >= 0;i--) {
    b[i] = b[i] << 1;
    if (i-1 >=0 && b[i-1] & INT_MAX_BIT_MASK)
      b[i]++;
  }
  return 0;
}

{
  int i;
  if (!p)
    return -1;
  b = p->b;
  for (i = 0;i < p->size;i++) {
    b[i] = b[i] >> 1;
    if (i+1 < p->size && (b[i+1] & 1))
      b[i] |= INT_MAX_BIT_MASK;
  }
  return 0;  
}

{
  unsigned int offset = n % INT_NBITS;
  unsigned int idx = n / INT_NBITS;
  if (!p)
    return -1;
  b = p->b;
  return (b[idx] & (1 << offset)) != 0;
}

{
  unsigned int offset = n % INT_NBITS;
  unsigned int idx = n / INT_NBITS;
  if (!p)
    return -1;
  b = p->b;
  b[idx] |= (1<<offset);
  return 0;
}

{
  unsigned int offset = n % INT_NBITS;
  unsigned int idx = n / INT_NBITS;
  if (!p)
    return -1;
  b = p->b;
  b[idx] &= ~(1<<offset);

  return 0;
}

{
  int j;
  if (!p)
    return;
  b = p->b;
    printf("%d", read_bit(p, j));
    if (j % INT_NBITS==0)
      printf("n");
  }
  printf("n");
  return;
}

{
  int n_int = 4;
  if (!p) {
    fprintf(stderr, "Out of memory!n");
    return EXIT_FAILURE;
  }

  set_bit(p, 1);
  set_bit(p, 127);
  print_bits(p);

  return 0;
}