Re: math.h float_t and double_t not typedef'ed when FLT_EVAL_METHOD defined

[Craig Howland <howland at LGSInnovations dot com>]

Jeff or Corinna:
Ping?  (Oddly enough, while I got my copy from the list server, I don't see this 
message in the mail archive.)
Craig


On 12/11/2012 05:57 PM, Craig Howland wrote:
> Here, finally, is a patch. I have changed the approach from what I first
> proposed to the alternative of not defining float_t and double_t when
> FLT_EVAL_METHOD is not recognized. The reasons are explained in the comments in
> the patch.
> The end result for the state of defining float_t and double_t will not be
> different for Jordy's test case, but the test case will pass because defining
> log2f() as a macro is now skipped for the case.
> Craig
>
> 2012-12-11 Craig Howland <howland@LGSInnovations.com>
>
> * libc/include/math.h: Add recognition of values 1 and 2 for
> FLT_EVAL_METHOD; do not define log2f() macro if float_t is not defined.
>
>
> On 11/16/2012 08:01 PM, Craig Howland wrote:
> > Yes, the manner in which math.h handles float_t and double_t is lacking, and
> > yes, the solution is quite similar to what you list. The problem is that the
> > else case is tricky, when the value is not 0, 1, or 2.
> >
> > ...
> >
> > The two approaches for unknown values are to default to something or to define
> > nothing. In the code below, you can see that I opted for the former, along with
> > the reason for so doing.
> >
> > ...
> >
> > Thoughts and comments on how to handle the if? Even though I made the tentative
> > choice of a default when I wrote this in 2010, my present inclination is that
> > nothing should be defined so that such an implementation would have to put them
> > in somehow for things which use them to work. (It would be less of a mess if the
> > standard had put float_t and double_t in float.h along with FLT_EVAL_METHOD.)
> >
> > Craig
> >
> >
> > On 11/16/2012 06:34 AM, Jordy Potman wrote:
> > > Hi,
> > >
> > > I am using Newlib with a clang based compiler for our architecture.
> > >
> > > I think I have found an issue in Newlib's math.h.
> > >
> > > Newlib's math.h does not typedef float_t and double_t when
> > > FLT_EVAL_METHOD is defined.
> > >
> > > math.h lines 143-147:
> > > 143: #ifndef FLT_EVAL_METHOD
> > > 144: #define FLT_EVAL_METHOD 0
> > > 145: typedef float float_t;
> > > 146: typedef double double_t;
> > > 147: #endif /* FLT_EVAL_METHOD */
> > >
> > > Clang's float.h defines FLT_EVAL_METHOD (I think gcc's float.h does as
> > > well), which I think is correct according to section 5.2.4.2.2 paragraph
> > > 8 of the C99 standard.
> > >
> > > Newlib's math.h defines the log2f function as a macro which uses
> > > float_t.
> > >
> > > math.h lines 354-357:
> > > 354: extern float log2f _PARAMS((float));
> > > 355: #if !defined(__cplusplus)
> > > 356: #define log2f(x) (logf (x) / (float_t) _M_LN2)
> > > 357: #endif
> > >
> > > This causes a compilation error if a program includes float.h before
> > > math.h and uses the log2f function:
> > > $ cat log2f_test.c
> > > #include<float.h>
> > > #include<math.h>
> > >
> > > float f(float a) {
> > > return log2f(a);
> > > }
> > > $ xentium-clang -std=c99 -c log2f_test.c
> > > log2f_test.c:5:10: error: use of undeclared identifier 'float_t'; did
> > > you mean 'float'?
> > > return log2f(a);
> > > ^
> > > /home/potman/opt/xentium-tools-1.0.beta9-linux64/bin/../sysroots/default/include/math.h:359:31:
> > >
> > > note: expanded from
> > > macro 'log2f'
> > > #define log2f(x) (logf (x) / (float_t) _M_LN2)
> > > ^
> > > 1 error generated.
> > >
> > > I have changed math.h lines 354-357 to the following in our
> > > implementation:
> > >
> > > #ifndef FLT_EVAL_METHOD
> > > #define FLT_EVAL_METHOD 0
> > > #endif /* FLT_EVAL_METHOD */
> > > #if FLT_EVAL_METHOD == 1
> > > typedef double float_t;
> > > typedef double double_t;
> > > #elif FLT_EVAL_METHOD == 2
> > > typedef long double float_t;
> > > typedef long double double_t;
> > > #else
> > > typedef float float_t;
> > > typedef double double_t;
> > > #endif
> > >
> > > This is my interpretation of how float_t and double_t should be
> > > typedef'ed depending on the value of FLT_EVAL_METHOD as is described in
> > > section 7.12 paragraph 2 of the C99 standard. However I am not a C99
> > > standard expert.
> > >
> > > Jordy

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