[boost] Math functions - requirements 'spec'

From: Paul A Bristow (pbristow_at_[hidden])
Date: 2004-11-04 08:35:50

Following the view of C and C++ Working groups at Redmond
that a working implementation of my proposal for math functions
was a necessary condition for consideration for a TR-2 standard,

I have been skirmishing with the problems of converting
Stephen Moshier's Cephes code into something that works for both C++ and C.

Several issues have emerged, mainly revealing my ignorance with C
- a state of bliss in which I would have preferred to remain ;-)

1  Should I no longer cater for non-compliant compilers (usually old-style
function specifications?

I only have MSVC 8.0 available.

2  How do I check that my code is Standard C compatible (as well as C++)?

3  How do I tell whether the compiler is a C compiler or a C++ compiler (for
#if ing).
  #if __cplusplus  #if _STDC__ ... ?

4  I have compiled a module #including <cmath> OK with explicit project
property "compile with C++", but when I change this to "compile with C" and
no extensions so the /Za option is on the command line, it does not define
__STDC__ == 1 as I have expected.  What am I doing wrong. 

5  Do I have to use exclusively C /* */ style comments :-((?  (Or can I
assume that C compilers will understand // comments?)

I have also immediately come up against the problems of IEEE 754 compliance,
argument checks, NaN, infs and exception throwing.

6  Should I assume IEEE 754 compliance and signal #error "Only works with
IEEE compliant compilers"?  How do I check with C - numeric_limits ::
is_IEC559 equivalent?  Or would it be foolish to rule out the some older DEC
machines?

7  Do you recommend making NaN and inf checks optional?

8  How do I find if they are available, automatically but portably?

9  Can I assume isnan(float, double and long double) with C and with C++?

10 How do I detect isinf?  Do I use FPclass for detecting isinf? (pos and
neg?)

11 Do you recommend making throwing exceptions optional with C++?

12  Should I scrap all the hexadecimal (mainly polynomial) constants on the
grounds that conforming compilers should read decimal digit strings
'correctly' - getting the nearest representable value.  Is this true for
both C and C++?

13  Do you also recommend making checking arguments optional (with #ifdefs)?
So that those who want the ultimate in speed at any risk can switch checking
off?

Comments welcome.

Paul

PS

Slightly updated versions of my TR2 proposal are at

http://www.hetp.u-net.com/public/math_stats_functions_tr2_v2.doc

http://www.hetp.u-net.com/public/math_stats_functions_tr2_v2.pdf

Paul A Bristow
Prizet Farmhouse, Kendal, Cumbria UK LA8 8AB
[phone]  [phone]
mailto: pbristow_at_[hidden]