Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!apple!oliveb!pyramid!prls!mips!winchester!mash
From: mash@mips.COM (John Mashey)
Newsgroups: comp.arch
Subject: Re: Integer Multiply/Divide on Sparc
Message-ID: <34530@mips.mips.COM>
Date: 16 Jan 90 16:52:34 GMT
References: <8840005@hpfcso.HP.COM> <1249@otc.otca.oz> <KHB.90Jan11212327@chiba.kbierman@sun.com> <1255@otc.otca.oz> <2819@auspex.auspex.com>
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Reply-To: mash@mips.COM (John Mashey)
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In article <2819@auspex.auspex.com> guy@auspex.auspex.com (Guy Harris) writes:
....
>the compiler writers were too lazy to change the compiler, I think it
>was done because it was *still* faster to do the shifts and adds.  I
>can't speak for MIPS, but I wouldn't be surprised to hear that even
>though they had a multiply instruction since Day 1 they still did shifts
>and adds for multiplies by constants.

Yes, of course: shifts, adds, and subtracts, up to the point where
it takes about as long as a multiply. (I think there's a bias to use
multiply if its equal or close, since the code sequence is shorter,
andthere may be code scheduling opportunities in the shadow of the
multiply, although not many.)
-- 
-john mashey	DISCLAIMER: <generic disclaimer, I speak for me only, etc>
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