On Wed, Feb 20, 2013 at 12:27 PM, Dennis E. Hamilton <dennis.hamil...@acm.org> wrote: > I don't want to get into this. I think enough has been said. > > I do want to avoid anyone misunderstanding what the ANSI/ISO Standards for C > and C++ say about pow(0,0) however. > > In general, C/C++ pow(0,0) is left implementation-defined. There may be a > domain error (this is an implementation-defined result plus setting of a > global condition). There may be a silent return of NaN. >
A domain error is something that an implementation might express via call to matherr() and setting errno to EDOM is a different question than the return value. I'm reading a requirement for pow(x,0) to return 1 for all values of x. Are you seeing something else? Are you seeing anything that says a conforming C/C++ runtime may *return* something other than 1? Btw, the rationale for this choice is described on page 182 of this document: http://www.open-std.org/jtc1/sc22/wg14/www/C99RationaleV5.10.pdf And I don't think cpow() is relevant to the topic. Regards, -Rob > - Dennis > > DETAILS > > In ISO/IEC 14882-1998 (C++) the numeric_limits account for specializations in > arithmetic that provide for +infinity and silent (non-exception-triggering) > NaN among other cases. The value for *complex* pow(0,0) is > implementation-defined in 26.2.8. For <cmath> (section 26.5) the definitions > are deferred to the C Standard <math.h>, although more type specializations > are provided for numtype pow(numtype1, numtype2). > > In ISO/IEC 14882-2003 (C++) is the same. I haven't checked -2011 and the > standardization of some of the Boost library. > > In ISO/IEC 9899:2011 (C) the specification of cpow( ) does not say anything > about cpow(0,0). The specification of pow(x,y) says that a domain error may > occur if x is zero and y is zero. The same language appears in ISO C99 > (including its Technical Corrigenda). In ANSI/ISO C (way back, before 1992) > the rule was that "A domain error occurs if the result cannot be represented > when x is zero and y is less than or equal to zero." (A domain error > involves return of an implementation-defined value and the global error > variable is set - exceptions aren't used in Standard C libraries.) So, > considerable variability is provided. Quiet NaN and +Inf are representations, > of course, if available in the library and arithmetic implementation. These > are accounted for in 9899:2011. > > Plauger's "Standard C Library" (in 1992) assumes IEEE floating point and > handles NaN and +Inf (and his implementation appears to return 1 for pow(0,0) > -- the code is pretty snarly). > > -----Original Message----- > From: Rob Weir [mailto:robw...@apache.org] > Sent: Wednesday, February 20, 2013 07:08 > To: dev@openoffice.apache.org > Subject: Re: Solving this 0⁰ issue correctly (was Re: Calc behavior: result > of 0 ^ 0) > > [ ... ] ANSI C, C99, ISO C++ all require that > pow(x,0) return 1 for all values of x. > > [ ... ] >
