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From: adrie@philica.ica.philips.nl (Adrie Koolen)
Newsgroups: comp.os.minix
Subject: Re: #! in MM -- take 2
Message-ID: <819@philica.ica.philips.nl>
Date: 28 May 91 09:04:23 GMT
References: <klamer.674467423@mi.eltn.utwente.nl> <10033@star.cs.vu.nl> <klamer.675068096@mi.eltn.utwente.nl> <10055@star.cs.vu.nl> <1991May24.164952.22295@Arco.COM>
Reply-To: adrie@beitel.ica.philips.nl (Adrie Koolen)
Organization: Philips TDS, Innovation Centre Aachen
Lines: 51

In article <1991May24.164952.22295@Arco.COM> dprrhb@inetg1.ARCO.COM (Reginald H. Beardsley) writes:
>  It is not the alignment of the characters that matters, it is the 
>alignment of the adjacent full word values that matters.  This means that
>in addition to starting the string on a word boundary, to needs to be 
>padded to a multiple of the word length.  For SPARC this will need to be
>4 bytes.  Even on systems that will tolerate the misalignment, there are 
>very significant performance penalties for breaking the alignment.

I compiled a program containing:

	char s1[] = "";
	char s2[] = "a";
	char s3[] = "ab";
	char s4[] = "abc";
	char s5[] = "abcd";
	char s6[] = "abcde";
	...
	printf("%08x, %08x, %08x, %08x, %08x, %08x.\n", s1, s2, s3, s4, s5, s6);

on a SparcStation. The Sun C compiler aligned all strings to word addresses:

	000040a8, 000040ac, 000040b0, 000040b4, 000040b8, 000040c0.

while the GNU C compiler put all strings one after the other without aligning
anything:

	000040a8, 000040a9, 000040ab, 000040ae, 000040b2, 000040b7.

It looks like string alignment is not necessary in ANSI C. But then again, maybe
I missed your point. Anyway, Minix-Sparc generates with the following program:

	main(int argc, char *argv[])
	  { int i;

	    for (i=0; i<argc; i++) printf("%08x: %s\n", argv[i], argv[i]);
	  }

and the invocation:

	proef d is een test

this output:

	00011F74: proef
	00011F7A: d
	00011F7C: is
	00011F7F: een
	00011F83: test

Adrie Koolen (adrie@ica.philips.nl)
Philips Innovation Centre Aachen