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From: pf@diab.UUCP (Per Fogelstrom)
Newsgroups: comp.arch
Subject: Re: Dhrystones & string ops [Was vectors]
Message-ID: <280@diab.UUCP>
Date: Sat, 1-Aug-87 06:24:59 EDT
Article-I.D.: diab.280
Posted: Sat Aug  1 06:24:59 1987
Date-Received: Tue, 4-Aug-87 04:28:21 EDT
References: <279@diab.UUCP> <17780@amdcad.AMD.COM>
Reply-To: pf@.UUCP (Per Fogelstrom)
Distribution: world
Organization: Diab Data AB, Taby, Sweden
Lines: 42
Keywords: String op's, Dhrystone, benchmarks
Summary: String instructions are useable.

In article <17780@amdcad.AMD.COM> tim@amdcad.UUCP (Tim Olson) writes:
+------
|In article <279@diab.UUCP> pf@.UUCP (Per Fogelstrom) writes:
|+-----
|| What this benchmark really tests is the compilers ability to remove code that
|| does'nt really do anything. And of course the cpu's ability to handle strings.
|| Just check the Am29000. The designers put in an instruction just to speed up
|| this benchmark.... Now what, have we reaced a new point, where cpu's are
|| designed for the bencmarks instead of vice versa, as it was before ????
|+-----
|No, we didn't put in the cpbyte instruction to "speed up Dhrystone" --
|it was added because many internal programs that we ran showed that such
|an instruction could be used to speed up C string handling (size
|unknown, string terminated by a \0) in general.
+------

Sorry ! Didn't wanted to pick on you.
Yes! The Am29000 is good at strings. But can one make use of such a instruction
(cpbyte) in compiler code generation?? Of course it is possible to use it in
assembly written librarys. But to often i have seen programs that do not make
use of the 'C' library string routines, mayby because they are inefficient.

+-------
|Many processors have specialized instructions for strings -- Intel's 80x86
|family (movs, cmps), AT&T's 32100 (strlen, strcmp), National's 32x32
|family (movs, cmps), NEC's V70 (movc, cmpc), Fairchild's Clipper (movc,
|cmpc macros).  However, most of these don't address "C-type" strings;
|they require a character count as a parameter.
+-------

Wrong! At least in the NS32x32 case. They do address "C-type" strings, and
many other string constructs as well, not only \0 terminated strings. The
character count parameter can be ignored if it is set to a 'huge' value
(e.g 2**32-1). I myslf is using string instructions in C-librarys and it is
possible to detect the "while( *p1++ = *p2++)" in a 'C' program. (We here
at Diab can in our C-compiler).

-- 
Per Fogelstrom,  Diab Data AB
SNAIL: Box 2029, S-183 02 Taby, Sweden
ANALOG: +46 8-7680660
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