bitvect.cpp

Thinking_in_C___2.rar

//: C07:Bitvect.cpp {O}
// From Thinking in C++, 2nd Edition
// at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// BitVector Implementation
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits> // CHAR_BIT = # bits in char
#include "../require.h"
#include "Bitvect.h"
using namespace std;
// A byte with the high bit set:
const unsigned char highbit =
  1 << (CHAR_BIT - 1);

BitVector::BitVector() {
  numBytes = 0;
  Bits = 0;
  bytes = 0;
}
// Notice default args are not duplicated:
BitVector::BitVector(unsigned char* init,
                     int size) {
  numBytes = size;
  Bits = numBytes * CHAR_BIT;
  bytes = (unsigned char*)calloc(numBytes, 1);
  require(bytes);
  if(init == 0) return; // Default to all 0
  // Translate from bytes into bit sequence:
  for(int index = 0; index<numBytes; index++)
    for(int offset = 0;
        offset < CHAR_BIT; offset++)
      if(init[index] & (highbit >> offset))
         set(index * CHAR_BIT + offset);
}

BitVector::BitVector(char* binary) {
  Bits = strlen(binary);
  numBytes =  Bits / CHAR_BIT;
  // If there's a remainder, add 1 byte:
  if(Bits % CHAR_BIT) numBytes++;
  bytes = (unsigned char*)calloc(numBytes, 1);
  require(bytes);
  for(int i = 0; i < Bits; i++)
    if(binary[i] == '1') set(i);
}

BitVector::~BitVector() {
  free(bytes);
}

void BitVector::set(int bit) {
  require(bit >= 0 && bit < Bits);
  int index = bit / CHAR_BIT;
  int offset = bit % CHAR_BIT;
  unsigned char mask = (1 << offset);
  bytes[index] |= mask;
}

int BitVector::read(int bit) {
  require(bit >= 0 && bit < Bits);
  int index = bit / CHAR_BIT;
  int offset = bit % CHAR_BIT;
  return (bytes[index] >> offset) & 1;
}

void BitVector::clear(int bit) {
  require(bit >= 0 && bit < Bits);
  int index = bit / CHAR_BIT;
  int offset = bit % CHAR_BIT;
  unsigned char mask = ~(1 << offset);
  bytes[index] &= mask;
}

int BitVector::bits() { return Bits; }

void BitVector::bits(int size) {
  int oldsize = Bits;
  Bits = size;
  numBytes =  Bits / CHAR_BIT;
  // If there's a remainder, add 1 byte:
  if(Bits % CHAR_BIT) numBytes++;
  void* v = realloc(bytes, numBytes);
  require(v);
  bytes = (unsigned char*)v;
  for(int i = oldsize; i < Bits; i++)
    clear(i); // Erase additional bits
}

void BitVector::print(const char* msg) {
  puts(msg);
  for(int i = 0; i < Bits; i++){
    if(read(i)) putchar('1');
      else putchar('0');
    // Format into byte blocks:
    if((i + 1) % CHAR_BIT == 0) putchar(' ');
  }
  putchar('\n');
} ///:~