Date: Mon, 05 May 2003 16:30:46 -0700 From: Peter Wemm <peter@wemm.org> To: Bruce Evans <bde@zeta.org.au> Cc: David O'Brien <obrien@FreeBSD.org> Subject: Re: cvs commit: src/lib/libc/amd64/gen fabs.S modf.S Message-ID: <20030505233046.AE7F82A8AE@canning.wemm.org> In-Reply-To: <20030502030109.B20181@gamplex.bde.org>
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Bruce Evans wrote: > On Thu, 1 May 2003, David O'Brien wrote: > > > On Thu, May 01, 2003 at 02:24:23AM +0300, Maxim Sobolev wrote: > > > Does this mean that it is theoretically possible to use those > > > and other similar functions on SSE2-capable ia32 processors, such > > > as p4, instead of x87 FPU ones? > > > > Probably. You'll have to do a little /%r/%e/ action. > > Not to mention changing the i386 calling convention. But you wouldn't > want to use these and other similar functions on SSEn-capable ia32 > processors, since they don't use SSEn except for using SSE1 registers > to pessimize the function call protocol a little for at least the > callee (the callee has to do extra work to move values from wrong > registers via the stack). Perhaps other unsimilar functions get > more benefits from SSE. > > BTW, is it really safe to use negative stack offsets for scratch > variables ? Where is the signal stack? fabs() and some other functions > use negative stack offsets, but modf() uses a normal frame pointer. Yes. There is a 128 byte 'red zone' below the stack pointer that may be used by leaf functions. Signals delivery is supposed to skip that space, but I haven't done that yet. Cheers, -Peter -- Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com "All of this is for nothing if we don't go to the stars" - JMS/B5
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