Re: Precision of floating point multiply

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Article #6506

#6506

From: Nick Maclaren
Date: Mon, 29 Sep 2003 15:21

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In article <xrXdb.631209$Ho3.121609@sccrnsc03>,
"Glen Herrmannsfeldt" <gah@ugcs.caltech.edu> writes:
|> 
|> I thought it was somewhere in the thread, but maybe not.
|> 
|> For  C=C+A*B, single precision A, B, and double precision C:
|> 
|>    LE 0,A   load single precision A
|>    ME 0,B   Multiply by B generating double product in float register 0
|>    SDR 2,2   Clear double float register 2
|>    LER 2,0    copy single value from reg 0 to reg 2
|>    AD 2,C     add double C
|>    STD 2,C    store double into C
|> 
|> The SDR and LER are used to clear the low half of the product.

If my memory is right, those two are NOT done as part of the
multiplication, but are the conversion from single to double
precision.  I.e. you would also get them in:

    C=C+A, single precision A, and double precision C.


Regards,
Nick Maclaren.

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From: nmm1@cus.cam.ac.uk (Nick Maclaren)
Newsgroups: comp.lang.fortran,comp.arch,bit.listserv.ibm-main,alt.folklore.computers
Subject: Re: Precision of floating point multiply
Date: 29 Sep 2003 15:21:17 GMT
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