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sysadm |
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/*
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* Copyright (C) 2000 Ross Combs (rocombs@cs.nmsu.edu)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*/
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/*****/
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#ifndef JUST_NEED_TYPES
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#ifndef INCLUDED_INTROTATE_PROTOS
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#define INCLUDED_INTROTATE_PROTOS
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/*
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* ROTL(x,n,w) rotates "w" bit wide value "x" by "n" bits to the left
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*
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* The expression passed in as x must have a type at least as wide as w.
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* The type should probably be unsigned for this to be guaranteed to work
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* properly. If n or w is signed and larger than x remember that the
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* promotion rules would promote x to be of the same (signed) type.
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*
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* Unfortunately C doesn't have rotate operations and they can be difficult
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* to implement when handling rotates by zero, negative numbers, or numbers
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* greater or equal to the bit width of the number. This is because ANSI/ISO
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* C makes weak guarantees about the left and right shift operators. We
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* would like to not depend on word size, endianness, or how negative
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* integers are represented. Unfortunately only some of those goals may be
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* achieved. As for optimization, a really good compiler might be able to
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* recognize what we are doing and turn it into a single machine instruction.
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*/
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/* valid for 0<n<w and w>0 */
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/*#define ROTL(x,n,w) (((x)<<(n)) | ((x)>>((w)-(n))))*/
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/* valid for 0<=n<w and w>0 */
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/*#define ROTL(x,n,w) (((x)<<(n)) | ((x)>>(((-(n))&(w-1)))))*/
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/* valid for 0<=n and w>0 , depends on 2's complement */
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#define ROTL(x,n,w) (((x)<<((n)&(w-1))) | ((x)>>(((-(n))&(w-1)))))
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/* valid for 0<=n and w>0 , uses three mods and an ugly conditional */
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/* FIXME: and also a bug because it doesn't work on PPC */
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/*#define ROTL(x,n,w) (((n)%(w)) ? (((x)<<((n)%(w))) | ((x)>>((w)-((n)%(w))))) : (x))*/
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#define ROTL32(x,n) ROTL(x,n,32)
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#define ROTL16(x,n) ROTL(x,n,16)
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#endif
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#endif
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