Date: Tue, 21 Aug 2007 12:40:06 GMT From: "Simun Mikecin" <numisemis@yahoo.com> To: freebsd-amd64@FreeBSD.org Subject: Re: amd64/115581: [patch] -mfancy-math-387 has no effect Message-ID: <200708211240.l7LCe6xP093265@freefall.freebsd.org>
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The following reply was made to PR amd64/115581; it has been noted by GNATS. From: "Simun Mikecin" <numisemis@yahoo.com> To: bug-followup@freebsd.org, brde@optusnet.com.au Cc: Subject: Re: amd64/115581: [patch] -mfancy-math-387 has no effect Date: Tue, 21 Aug 2007 14:12:29 +0200 On Fri, 17 Aug 2007, Bruce Evans wrote: > It should not be used, especially on amd64 systems since basic FP > instructions are relatively fast compared with the fancy instructions > (except for sqrt). The 64-bit amd64 libm intentionally never uses the > fancy instructions (except for sqrt), partly because they are not much > faster and partly because they are much less accurate. The fancy > instructions are not used for float precision (unless you pessimize > things using -mfancy-math-387) since they are about 3 times slower > than the library versions on small args. This PR is about -mfancy-math-387 usage when compiling 32-bit compatibility libraries that are gone be used on FreeBSD/amd64. As far as I can see FreeBSD's libm on i386 uses those fancy instructions (for example /usr/src.current/lib/msun/i387/s_sin.S), so the same libm will be used for running 32-bit apps on FreeBSD/amd64. Is your statement about fancy instructions been 3 times slower also valid for FreeBSD/i386 and 32-bit apps running on FreeBSD/amd64?home | help
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