Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!SUMEX-AIM.STANFORD.EDU!Rice
From: Rice@SUMEX-AIM.STANFORD.EDU (James Rice)
Newsgroups: comp.sys.ti.explorer
Subject: Re: fixnum vs single-float multiplies
Message-ID: <2833815478-9531059@KSL-EXP-6>
Date: 19 Oct 89 18:57:58 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: inet
Organization: The Internet
Lines: 20

@i[I] would expect that short float and fixnum
multiplication times should be very similar.  This is
because to do the short float multiple you simply multiply
the two mantissae and ADD the exponents.  The addition of
the exponents can be done in parallel to the multiple of
the mantissae and should be faster.  How many bits are
there in the mantissa of an Explorer short float?  If
there are fewer than in a fixnum then I would expect it to
be a little faster (modulo any mysterious IEEE behaviour
checking).  Floating point addition is the thing that
really screws you, since you have to slide the two
mantissae until the exponents match before you can perform
the addition.  All of those arithmetic shifts can be slow.




Rice.

(mind you they may simply have screwed up the ucode).