bits.c

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/***********************************************************************
  bits.c
  BITWISE OPERATIONS, functions to manipulate bits.  Max Luttrell,
  3/17/96
*/

#include "standard.h"

byte getbit(byte b, int n)
/*
  get value of bit in position n from byte b,
  where a byte has positions 12345678
*/
{
  return (b >> (8-n)) & 1;
}

unsigned int getbitint(unsigned int b, int n)
/*
  get value of bit in position n from unsigned int b,
  where an unsigned integer has positions 1234567890123456
*/
{
  return (b >> (16-n)) & 1;
}


void setbit(byte *b, int n, byte v)
/*
  set value of bit in position n of byte b to be the value v.
  a byte has positions 12345678
  input: pointer to the byte.  output: none.  side effect: changes
  the particular bit in the byte
*/
{
  if (v != 0)
    *b = (*b | (128 >> (n-1))); /*turn the bit on*/
  else
    *b = (*b & (~(128 >> (n-1)))); /*turn the bit off*/
}


void setbitint(unsigned int *b, int n, byte v)
/*
  set value of bit in position n of unsigned int b to be the value v.

                             MSB      1   LSB 
        a byte has positions 1234567890123456
  input: pointer to the unsigned int.  output: none.  side effect: 
        changes the particular bit in the byte
*/
{
  if (v != 0)
    *b = (*b | (32768 >> (n-1))); /*turn the bit on*/
  else
    *b = (*b & (~(32768 >> (n-1)))); /*turn the bit off*/
}

void printbyte(byte b)
/* prints a byte to std output */
{
  int j;
  for(j=7;j>=0;j--)
    if ((int) b  & (1 << j))
      printf("1");
    else
      printf("0");
  printf("\n");
}

void printint(unsigned int b)
/* prints an unsigned int to std output */
{
  int j;
  for(j=15;j>=0;j--)
    if ((int) b  & (1 << j))
      printf("1");
    else
      printf("0");
  printf("\n");
}


int random_bit(void)
/*
 * returns: either a 1 or a 0.  
 *
 * there is approximately an equal chance of each.
 */
{
  static int random_counter = -1;
  static int r;
 
  if (random_counter == -1) {
    r = rand();
    random_counter = 30;
  }
  return ((r & (1 << random_counter--))?1:0);
}

void randomize_byte(byte *b)
/*
 * sets the bits inside of byte b to random values
 */
{
  int i;

  for (i=1;i<=8;i++)
    setbit(b,i,random_bit());
}

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