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From: kenny@uiucdcsb.CS.UIUC.EDU
Newsgroups: net.lang.c
Subject: Re: Re: Float Double Parameters
Message-ID: <139200025@uiucdcsb>
Date: Fri, 11-Apr-86 10:38:00 EST
Article-I.D.: uiucdcsb.139200025
Posted: Fri Apr 11 10:38:00 1986
Date-Received: Mon, 21-Apr-86 07:57:36 EST
References: <5216@alice>
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Nf-ID: #R:alice:-521600:uiucdcsb:139200025:000:1419
Nf-From: uiucdcsb.CS.UIUC.EDU!kenny    Apr 11 09:38:00 1986


/* Written 10:34 pm  Apr  7, 1986 by herndon@umn-cs in uiucdcsb:net.lang.c */
  As far as I know (admittedly, not far) there is no longer any
good reason for the current schizophrenia about single/double
precision arithmetic, other than historical precedent.  Does
anyone know any other good reasons, such as design faults in
the VAX FPA?

				Robert Herndon
/* End of text from uiucdcsb:net.lang.c */

No, but you have (possibly) the wrong historical precedent.  On the GE 635
(and its successors), *all* floating-point arithmetic was double-precision
internally.  Single-precision *instructions* existed, but all they did was
to pad or truncate the operand appropriately.  The GE Fortran library's
mathematical functions all, therefore, accepted only double-precision
operands (SIN and DSIN were the same function).  When BCPL was built for the
635, it borrowed the existing Fortran library and hence had to adopt the
convention that all float's are promoted to double's for parameter passing.
'B' (Anyone else remember 'B'?  It was a neat language [compared to what was
available before 'C']) and later 'C' inherited this kludge from BCPL.

Kevin Kenny
University of Illinois at Urbana-Champaign
UUCP: {ihnp4,pur-ee,convex}!uiucdcs!kenny 
CSNET:	kenny@UIUC.CSNET
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"Yes, understanding today's complex world is a bit like having bees live in
your head, but there they are."