mirror of https://github.com/cc65/cc65.git
128 lines
4.5 KiB
C
128 lines
4.5 KiB
C
/*****************************************************************************/
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/* */
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/* shift.c */
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/* */
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/* Safe shift routines */
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/* */
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/* */
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/* */
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/* (C) 2003 Ullrich von Bassewitz */
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/* Roemerstrasse 52 */
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/* D-70794 Filderstadt */
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/* EMail: uz@cc65.org */
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/* */
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/* */
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/* This software is provided 'as-is', without any expressed or implied */
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/* warranty. In no event will the authors be held liable for any damages */
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/* arising from the use of this software. */
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/* */
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/* Permission is granted to anyone to use this software for any purpose, */
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/* including commercial applications, and to alter it and redistribute it */
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/* freely, subject to the following restrictions: */
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/* */
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/* 1. The origin of this software must not be misrepresented; you must not */
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/* claim that you wrote the original software. If you use this software */
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/* in a product, an acknowledgment in the product documentation would be */
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/* appreciated but is not required. */
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/* 2. Altered source versions must be plainly marked as such, and must not */
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/* be misrepresented as being the original software. */
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/* 3. This notice may not be removed or altered from any source */
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/* distribution. */
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/* */
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/*****************************************************************************/
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/* According to the C standard, shifting a data type by the number of bits it
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** has causes undefined behaviour. So
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**
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** unsigned long l = 1;
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** unsigned u =32;
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** l <<= u;
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**
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** may be illegal. The functions in this module behave safely in that respect,
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** and they use proper casting to distinguish signed from unsigned shifts.
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** They are not a general purpose replacement for the shift operator!
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*/
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#include <limits.h>
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/* common */
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#include "shift.h"
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/*****************************************************************************/
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/* Code */
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/*****************************************************************************/
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long asl_l (long l, unsigned count)
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/* Arithmetic shift left l by count. */
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{
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while (1) {
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if (count >= CHAR_BIT * sizeof (l)) {
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l <<= (CHAR_BIT * sizeof (l) - 1);
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count -= (CHAR_BIT * sizeof (l) - 1);
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} else {
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l <<= count;
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break;
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}
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}
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return l;
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}
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long asr_l (long l, unsigned count)
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/* Arithmetic shift right l by count */
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{
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while (1) {
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if (count >= CHAR_BIT * sizeof (l)) {
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l >>= (CHAR_BIT * sizeof (l) - 1);
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count -= (CHAR_BIT * sizeof (l) - 1);
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} else {
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l >>= count;
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break;
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}
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}
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return l;
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}
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unsigned long shl_l (unsigned long l, unsigned count)
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/* Logical shift left l by count */
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{
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while (1) {
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if (count >= CHAR_BIT * sizeof (l)) {
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l <<= (CHAR_BIT * sizeof (l) - 1);
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count -= (CHAR_BIT * sizeof (l) - 1);
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} else {
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l <<= count;
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break;
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}
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}
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return l;
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}
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unsigned long shr_l (unsigned long l, unsigned count)
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/* Logical shift right l by count */
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{
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while (1) {
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if (count >= CHAR_BIT * sizeof (l)) {
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l >>= (CHAR_BIT * sizeof (l) - 1);
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count -= (CHAR_BIT * sizeof (l) - 1);
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} else {
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l >>= count;
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break;
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}
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}
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return l;
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}
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