Xref: utzoo comp.lang.fortran:4208 comp.lang.c:34355
Path: utzoo!utgpu!watserv1!watmath!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!wuarchive!uunet!validgh!dgh
From: dgh@validgh.com (David G. Hough on validgh)
Newsgroups: comp.lang.fortran,comp.lang.c
Subject: Fortran vs C
Message-ID: <219@validgh.com>
Date: 29 Nov 90 14:06:06 GMT
Followup-To: poster
Organization: validgh, PO Box 20370, San Jose, CA 95160
Lines: 26

There have been recent statements that functions like sqrt() are
equivalent in Fortran and C.   This is incorrect.

In C, sqrt() is simply a function invocation.  It has no known
semantics unless #include <math.h> has been seen, in which case
ANSI-C knows that it is a double-precision function of a double-precision
argument.  Thanks to the default conversions, you can use sqrt on float
arguments with correct results, but they may take twice as long to compute
as necessary if you really meant sqrtf().
sqrt() won't work on long double arguments unless long double == double.

In Fortran, sqrt() is a generic intrinsic function, really an operator like +.  
Its semantics are known to the compiler.  The precision of the sqrt operation
can match that of the operand.

As mentioned by others, ANSI-C defines exception handling for the sqrt() function
and not for operators.  On high-performance implementations, error checking,
involving a conditional test and branch, can take as long as the sqrt
operation itself, even if performed inline.  System V implementations are
worse, requiring an external call to matherr(), although this will be 
removed in a future version of SVID.
-- 

David Hough

dgh@validgh.com		uunet!validgh!dgh	na.hough@na-net.stanford.edu