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From: spain@alliant.UUCP
Newsgroups: comp.arch
Subject: Re: How does compiled code use the floating point unit?
Message-ID: <362@alliant.UUCP>
Date: Wed, 10-Dec-86 01:44:29 EST
Article-I.D.: alliant.362
Posted: Wed Dec 10 01:44:29 1986
Date-Received: Sun, 14-Dec-86 07:11:43 EST
References: <394@houxs.UUCP>
Reply-To: spain@alliant.UUCP (Dave Spain)
Organization: Alliant Computer Systems, Littleton, MA
Lines: 15

In article <394@houxs.UUCP> daw@houxs.UUCP (D.WOLVERTON) writes:
>
>In some systems, the hardware floating point (fp) unit is _optional_.
>...
>	Are there other scenarios in use?

I am familiar with one more mechanism, call it 3.5 which goes something
like:

3.5)  Code generation pretends that the fp unit will always be present,
so it emits code which uses the fp unit directly in the instruction
stream. If a fp unit is not present, the "hardware" in the form of the
machines' microcode, emulates the instruction using the machine's integer
hardware. No OS trapping is involved and there is no change of control from
the user's code.