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From: cik@l.cc.purdue.edu (Herman Rubin)
Newsgroups: comp.lang.c
Subject: Swap
Message-ID: <661@l.cc.purdue.edu>
Date: 20 Jan 88 12:24:16 GMT
References: <3819@sigi.Colorado.EDU> <5080013@hpfcdc.HP.COM> <7120@brl-smoke.ARPA> <3203@bunker.UUCP>
Organization: Purdue University Statistics Department
Lines: 17
Summary: It always works if the compiler does not mess it up

If the hardware does not have a swap instruction, the following (which I
believe is easier to read than what was originally posted) is likely to be
as fast as any other way to exchange two entities of the same size, assuming
that the exclusive or equal operation is in hardware, and that the operation
does not introduce access conflicts:

	a ^= b;
	b ^= a;
	a ^= b;

I have used it on various machines.  Of course, a particular implementation
of C might not let you use it on pointers or floats; this is a defect in C,
as there is no way the hardware can give the wrong answer(s).
-- 
Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907
Phone: (317)494-6054
hrubin@l.cc.purdue.edu (ARPA or UUCP) or hrubin@purccvm.bitnet