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Path: utzoo!utcsri!flaps
From: flaps@utcsri.UUCP (Alan J Rosenthal)
Newsgroups: comp.lang.c
Subject: Re: C and Floating Point
Message-ID: <4521@utcsri.UUCP>
Date: Sat, 4-Apr-87 23:50:37 EST
Article-I.D.: utcsri.4521
Posted: Sat Apr  4 23:50:37 1987
Date-Received: Sun, 5-Apr-87 12:54:23 EST
References: <15958@sun.uucp>
Reply-To: flaps@utcsri.UUCP (Alan J Rosenthal)
Organization: University of Toronto
Lines: 35
Keywords: C Fortran Floating Point
Summary: 


In article <15958@sun.uucp> dgh@sun.UUCP writes:
>Fortran was created before the phrase "computer science" was imagined,
>by people who were trained as applied mathematicians.  Consequently they had
>some familiarity with what was needed and what had been done by 
>mathematicians over the past several centuries.   It would never have
>occurred to them, for instance, to disregard parentheses while evaluating
>expressions or to disallow equality comparison of numbers!

Ahem.

1.  Give any applied mathematician a calculator and the expression
"(57382 * 23) + (57382 * 2)".  They will ALL punch "57382 * 25" on the
calculator.  They know that parentheses can be rearranged.  (obviously not
disregarded, C doesn't do that.)

2.  Kernighan and Plauger, in _The_Elements_of_Programming_Style_, note that
the version of fortran at their local installation fails on an equality test
when one number is on an input punch-card and the other, identically typed
and also a constant, is in a program.  This is because different scanning
routines were used in the i/o library compiled with the fortran program and
the i/o routines that were part of the fortran compiler!  So much for
floating-point equality in fortran.  It's just a fact of life that you can't
count on floating-point equality (although nothing in C parallels the idiocy
of having two versions of a floating-point number scanning routine).

-- 

Alan J Rosenthal

flaps@csri.toronto.edu, {seismo!utai or utzoo}!utcsri!flaps,
flaps@toronto on csnet, flaps at utorgpu on bitnet.

"Probably the best operating system in the world is the [operating system]
made for the PDP-11 by Bell Laboratories." - Ted Nelson, October 1977