rotation.cpp

Think in C++ 第二版源码

//: C03:Rotation.cpp {O}
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// Perform left and right rotations

unsigned char rol(unsigned char val) {
  int highbit;
  if(val & 0x80) // 0x80 is the high bit only
    highbit = 1;
  else
    highbit = 0;
  // Left shift (bottom bit becomes 0):
  val <<= 1;
  // Rotate the high bit onto the bottom:
  val |= highbit;
  return val;
}

unsigned char ror(unsigned char val) {
  int lowbit;
  if(val & 1) // Check the low bit
    lowbit = 1;
  else
    lowbit = 0;
  val >>= 1; // Right shift by one position
  // Rotate the low bit onto the top:
  val |= (lowbit << 7);
  return val;
} ///:~