RFA: Add definition of M_LOG2_E when compiling in ISO C99 mode

[Jeff Johnston]

Thanks Nick for pointing this out.  I have made a patch, slightly 
different than yours, that fixes the problem.  Basically, I just defined 
a macro _M_LOG2E that is defined regardless.  The macro is used by log2 
and log2f and M_LOG2E uses it as well.

-- Jeff J.

Nick Clifton wrote:
> Hi Jeff,
> 
>   I ran across a small problem with the definition of the log2 macro
>   in newlib/libc/include/math.h.  The problem is that the macro is
>   defined when compiling in ISO C99 mode, but that the M_LOG2_E value
>   that it uses is not.  Here is an example:
> 
>     % cat foo.c
>     #include <math.h>
>     int main (void) { return (int) log2 (0.0); }
> 
>     % newlib-using-gcc -std=c99 -c foo.c
>     foo.c: In function 'main':
>     foo.c:2: error: 'M_LOG2_E' undeclared (first use in this function)
> 
>   The patch below fixes this problem by adding a definition of M_LOG2_E
>   if the log2 macro has been defined but the constant has not.
> 
>   OK to apply ?
> 
> Cheers
>   Nick
> 
> newlib/ChangeLog
> 2007-09-06  Nick Clifton  <nickc@redhat.com>
> 
> 	* libc/include/math.h (M_LOG2_E): Ensure that this macro is
> 	defined if the log2 macro is defined.
> 
> Index: newlib/libc/include/math.h
> ===================================================================
> RCS file: /cvs/src/src/newlib/libc/include/math.h,v
> retrieving revision 1.28
> diff -c -3 -p -r1.28 math.h
> *** newlib/libc/include/math.h	11 Jul 2007 18:09:08 -0000	1.28
> --- newlib/libc/include/math.h	6 Sep 2007 11:33:55 -0000
> *************** extern __IMPORT _LIB_VERSION_TYPE _LIB_V
> *** 464,469 ****
> --- 464,473 ----
>   
>   #endif /* ! defined (__STRICT_ANSI__) */
>   
> + #if defined log2 && ! defined M_LOG2_E
> + #define M_LOG2_E        0.693147180559945309417
> + #endif
> + 
>   _END_STD_C
>   
>   #ifdef __FAST_MATH__
>