ack/lang/cem/cpp.ansi/arith.h

/*
 * (c) copyright 1987 by the Vrije Universiteit, Amsterdam, The Netherlands.
 * See the copyright notice in the ACK home directory, in the file "Copyright".
 */
/* $Id$ */
/* COMPILER ARITHMETIC */

/*	Normally the compiler does its internal arithmetics in longs
	native to the source machine, which is always good for local
	compilations, and generally OK too for cross compilations
	downwards and sidewards.  For upwards cross compilation and
	to save storage on small machines, SPECIAL_ARITHMETICS will
	be handy.
*/

/*	All preprocessor arithmetic should be done in longs.
*/
#define	arith	long				/* dummy */

#define	arith_size	(sizeof(arith))
#define	arith_sign	((arith) 1 << (arith_size * 8 - 1))
#define	max_arith	(~arith_sign)
Initial revision 1989-10-23 10:35:56 +00:00			`/*`
			`* (c) copyright 1987 by the Vrije Universiteit, Amsterdam, The Netherlands.`
			`* See the copyright notice in the ACK home directory, in the file "Copyright".`
			`*/`
Header --> Id 1994-06-24 14:02:31 +00:00			`/* $Id$ */`
Initial revision 1989-10-23 10:35:56 +00:00			`/* COMPILER ARITHMETIC */`

			`/* Normally the compiler does its internal arithmetics in longs`
			`native to the source machine, which is always good for local`
			`compilations, and generally OK too for cross compilations`
			`downwards and sidewards. For upwards cross compilation and`
			`to save storage on small machines, SPECIAL_ARITHMETICS will`
			`be handy.`
			`*/`

			`/* All preprocessor arithmetic should be done in longs.`
			`*/`
			`#define arith long /* dummy */`
Use (arith) 1 << ... when getting the sign bit. This prevents an overflow reported by @hexcoder- in https://github.com/davidgiven/ack/issues/56 lang/cem/cpp.ansi/LLlex.c used a plain 1 << ... and caused an overflow on machines where sizeof(int) < sizeof(long). Using 1L << ... would work for now but might fail later if arith became long long. C doesn't specify whether negative integers use 2's complement or some other format. Therefore, (arith) 1 << ... has an undefined value. It should still work because the value is some integer where the sign bit is set and all other bits are clear. (unsigned arith) 1 << ... would also get the sign bit, but casting it from unsigned back to signed would make the same undefined value. (arith) -1 << ... would assume 2's complement. 2017-10-29 21:45:10 +00:00
			`#define arith_size (sizeof(arith))`
			`#define arith_sign ((arith) 1 << (arith_size * 8 - 1))`
			`#define max_arith (~arith_sign)`