Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!amdcad!cayman!tim
From: tim@cayman.amd.com (Tim Olson)
Newsgroups: comp.misc
Subject: Re: IEEE floating point format
Message-ID: <26756@amdcad.AMD.COM>
Date: 14 Aug 89 18:17:04 GMT
References: <2170002@hpldsla.HP.COM> <9697@alice.UUCP> <3554@buengc.BU.EDU> <9725@alice.UUCP> <3591@buengc.BU.EDU> <152@servio.UUCP> <3707@buengc.BU.EDU>
Sender: news@amdcad.AMD.COM
Reply-To: tim@amd.com (Tim Olson)
Organization: Advanced Micro Devices, Austin, TX
Lines: 26
Summary:
Expires:
Sender:
Followup-To:

In article <3707@buengc.BU.EDU> bph@buengc.bu.edu (Blair P. Houghton) writes:
| In article <152@servio.UUCP> penneyj@servio.UUCP (D. Jason Penney) writes:
| >In article <3591@buengc.BU.EDU> bph@buengc.bu.edu (Blair P. Houghton) writes:
| >>Next question:  do C compilers (math libraries, I expect I should mean)
| >>on IEEE-FP-implementing machines generally limit doubles to normalized
| >>numbers, or do they blithely allow precision to waft away in the name
| >>of a slight increase in the number-range?
| >
| >This is an interesting question.  The early drafts of IEEE P754 had a
| >"warning mode" -- When "warning mode" was set, an operation with
| >normal operands that produced a subnormal result 
| >("subnormal" is the preferred term instead of "denormalized" now, by the way),
| >an exception was signalled.
| 
| Ulp!  You mean it does it absolutely silently now?  No provision at all
| for a hardware (or software) portabl-ized belief that an implementation
| will always perk up when the bits start to disappear??  I'm less impressed.

No, there are two exceptions that can be signalled: underflow and
inexact.  Underflow occurs when "tininess" is detected (or both tininess
and loss of accuracy, if traps are disabled).  Inexact occurs whenever
the rounded result of an operation cannot be represented exactly.

	-- Tim Olson
	Advanced Micro Devices
	(tim@amd.com)