/* shift.c
 * For use in CSE351 Lec 5 on Integers
 *
 * Demonstrates the different effects of right and left shifting
 * in combination with signed and unsigned "8-bit" data.
 */
#include <stdio.h>


int main() {
  // IMPORTANT: printf assumes most integral types are 32-bits.

  printf("\n");
  printf("** Left Shift (<<) **\n");

  unsigned char x = 0x19;
  unsigned char L1 = x<<2;
  unsigned char L2 = x<<3;
  unsigned char L3 = x<<4;

  // Show the shifted bit pattern by outputting in hex (%.2X formats the
  // output as >=2 capital hex digits)
  printf("*      Hex: x = 0x%.2X, L1 = 0x%.2X, L2 = 0x%.2X, L3 = 0x%.2X\n",
         x, L1, L2, L3);

  // Leave the type alone to show their interpretation as unsigned values.
  printf("* Unsigned: x = %4u, L1 = %4u, L2 = %4u, L3 = %4u\n",
         x, L1, L2, L3);
  // Explicitly cast to a signed char, to show how these bit patterns are
  // interpreted as signed values (%4 just means to pad to 4 characters in
  // length)
  printf("*   Signed: x = %4d, L1 = %4d, L2 = %4d, L3 = %4d\n",
         (char)x, (char)L1, (char)L2, (char)L3);


  printf("\n*********************\n");


  printf("\n");
  printf("** Right Shift (>>) **\n");

  // Recall that right-shifting an UNsigned value performs a logical
  // shift (ie, fills with 0s), and that right shifting a SIGNED value
  // performs an arithmetic shift (ie, fill with the sign bit).
  unsigned char xu = 0xF0;
  char          xs = 0xF0;
  unsigned char R1u = xu>>3;
  char          R1s = xs>>3;
  unsigned char R2u = xu>>5;
  char          R2s = xs>>5;

  // As before, we show the shifted bit pattern (first column) followed by
  // the values' interpretation as an unsigned integer.  This limits us to
  // only showing the logical right shift (since you can't have a logical
  // shift of a signed value).
  printf("Logical:\n");
  printf("*      Hex: xu = 0x%.2X, R1 = 0x%.2X, R2 = 0x%.2X\n",
         xu, R1u, R2u);
  printf("* Unsigned: xu = %4u, R1 = %4u, R2 = %4u\n",
         xu, R1u, R2u);

  printf("\n");

  printf("Arithmetic:\n");
  printf("*    Hex: xu = 0x%.2X, R1 = 0x%.2X, R2 = 0x%.2X\n",
         // cast to unsigned to prevent printf's unwanted sign extension
         (unsigned char)xs, (unsigned char)R1s, (unsigned char)R2s);
  printf("* Signed: xu = %4d, R1 = %4d, R2 = %4d\n",
         xs, R1s, R2s);


  // main() function in C is supposed to return an int; this return value
  // is used by the OS to determine the program's status.
  return 0;
}