Confused aboth math.in.h

[Gisle Vanem]

I'm trying to understand the logic behind the generation
of some statements in math.h (from math.in.h). The MSVC
compiler has cosf() defined as a macro in it's <math.h>:
  #define cosf(x)     ((float)cos((double)(x)))

(for x86,C). Then how is Gnulib supposed to replace that?
Since no matter what's put in Gnulib's "math.h", the
preprocessed output of cosf.c contains this rubbish:

  extern int gl_signbitl (long double arg);
  float
  ((float)cos((double)(float x)))  << MSVC's macro for cosf()
  {
    return (float) cos ((double) x);
  }

Isn't there supposed to be an "#undef cosf" in "math.h"
in this case? All I see is:
  # if address@hidden@     << line 448
  #  undef cosf

I assume if some vendor have 'cosf' it should be undefined
before Gnulib is trying to override or replace it. Not vice
versa. So shouldn't this be:
  # if @HAVE_COSF@ || @REPLACE_COSF@
  #  undef cosf

Also, in test-cosf.c, the
  SIGNATURE_CHECK (cosf, float, (float));

doesn't compile/link as it is here now (this macro cannot
contain another macro). Or maybe test-cosf.c isn't supposed
to be compiled for MSVC?

Please help me resolve my confusion.

Same for coshf(), cosl() etc. AFAICS.

--
--gv