git.sur5r.net Git - cc65/blob - src/common/shift.c

   1 /*****************************************************************************/
   2 /*                                                                           */
   3 /*                                  shift.c                                  */
   4 /*                                                                           */
   5 /*                            Safe shift routines                            */
   6 /*                                                                           */
   7 /*                                                                           */
   8 /*                                                                           */
   9 /* (C) 2003      Ullrich von Bassewitz                                       */
  10 /*               Roemerstrasse 52                                            */
  11 /*               D-70794 Filderstadt                                         */
  12 /* EMail:        uz@cc65.org                                                 */
  13 /*                                                                           */
  14 /*                                                                           */
  15 /* This software is provided 'as-is', without any expressed or implied       */
  16 /* warranty.  In no event will the authors be held liable for any damages    */
  17 /* arising from the use of this software.                                    */
  18 /*                                                                           */
  19 /* Permission is granted to anyone to use this software for any purpose,     */
  20 /* including commercial applications, and to alter it and redistribute it    */
  21 /* freely, subject to the following restrictions:                            */
  22 /*                                                                           */
  23 /* 1. The origin of this software must not be misrepresented; you must not   */
  24 /*    claim that you wrote the original software. If you use this software   */
  25 /*    in a product, an acknowledgment in the product documentation would be  */
  26 /*    appreciated but is not required.                                       */
  27 /* 2. Altered source versions must be plainly marked as such, and must not   */
  28 /*    be misrepresented as being the original software.                      */
  29 /* 3. This notice may not be removed or altered from any source              */
  30 /*    distribution.                                                          */
  31 /*                                                                           */
  32 /*****************************************************************************/
  33
  34
  35
  36 /* According to the C standard, shifting a data type by the number of bits it
  37 ** has causes undefined behaviour. So
  38 **
  39 **      unsigned long l = 1;
  40 **      unsigned u =32;
  41 **      l <<= u;
  42 **
  43 ** may be illegal. The functions in this module behave safely in that respect,
  44 ** and they use proper casting to distinguish signed from unsigned shifts.
  45 ** They are not a general purpose replacement for the shift operator!
  46 */
  47
  48
  49
  50 #include <limits.h>
  51
  52 /* common */
  53 #include "shift.h"
  54
  55
  56
  57 /*****************************************************************************/
  58 /*                                   Code                                    */
  59 /*****************************************************************************/
  60
  61
  62
  63 long asl_l (long l, unsigned count)
  64 /* Arithmetic shift left l by count. */
  65 {
  66     while (1) {
  67         if (count >= CHAR_BIT * sizeof (l)) {
  68             l <<= (CHAR_BIT * sizeof (l) - 1);
  69             count -= (CHAR_BIT * sizeof (l) - 1);
  70         } else {
  71             l <<= count;
  72             break;
  73         }
  74     }
  75     return l;
  76 }
  77
  78
  79
  80 long asr_l (long l, unsigned count)
  81 /* Arithmetic shift right l by count */
  82 {
  83     while (1) {
  84         if (count >= CHAR_BIT * sizeof (l)) {
  85             l >>= (CHAR_BIT * sizeof (l) - 1);
  86             count -= (CHAR_BIT * sizeof (l) - 1);
  87         } else {
  88             l >>= count;
  89             break;
  90         }
  91     }
  92     return l;
  93 }
  94
  95
  96
  97 unsigned long shl_l (unsigned long l, unsigned count)
  98 /* Logical shift left l by count */
  99 {
 100     while (1) {
 101         if (count >= CHAR_BIT * sizeof (l)) {
 102             l <<= (CHAR_BIT * sizeof (l) - 1);
 103             count -= (CHAR_BIT * sizeof (l) - 1);
 104         } else {
 105             l <<= count;
 106             break;
 107         }
 108     }
 109     return l;
 110 }
 111
 112
 113
 114 unsigned long shr_l (unsigned long l, unsigned count)
 115 /* Logical shift right l by count */
 116 {
 117     while (1) {
 118         if (count >= CHAR_BIT * sizeof (l)) {
 119             l >>= (CHAR_BIT * sizeof (l) - 1);
 120             count -= (CHAR_BIT * sizeof (l) - 1);
 121         } else {
 122             l >>= count;
 123             break;
 124         }
 125     }
 126     return l;
 127 }