math.h: match other OSes more closely.

isnan() and isinf() are type-generic macros, not usually declared as functions. Remove the function declarations and the big comment talking about how we shouldn't expose them.

isnanl() and isinfl() are exposed as functions by glibc (but not the BSDs), and we've always had the definitions, so we can increase source compatibility there trivially.

See the discussion on llvm/llvm-project#96008 for more background.

Change-Id: I798153f710794870bb4864f2ae8b98147f9d8763

Author: enh-google

libc/include/math.h

@@ -308,20 +308,6 @@ long double fmal(long double __x, long double __y, long double __z);
 #define islessgreater(x, y) __builtin_islessgreater((x), (y))
 #define isunordered(x, y) __builtin_isunordered((x), (y))
 
-/*
- * https://code.google.com/p/android/issues/detail?id=271629
- * To be fully compliant with C++, we need to not define these (C doesn't
- * specify them either). Exposing these means that isinf and isnan will have a
- * return type of int in C++ rather than bool like they're supposed to be.
- *
- * GNU libstdc++ 4.9 isn't able to handle a standard compliant C library. Its
- * <cmath> will `#undef isnan` from math.h and only adds the function overloads
- * to the std namespace, making it impossible to use both <cmath> (which gets
- * included by a lot of other standard headers) and ::isnan.
- */
-int (isinf)(double __x) __attribute_const__;
-int (isnan)(double __x) __attribute_const__;
-
 /* POSIX extensions. */
 
 extern int signgam;
@@ -362,6 +348,7 @@ double gamma(double __x);
 double scalb(double __x, double __exponent);
 double drem(double __x, double __y);
 int finite(double __x) __attribute_const__;
+int isinff(float __x) __attribute_const__;
 int isnanf(float __x) __attribute_const__;
 double gamma_r(double __x, int* _Nonnull __sign);
 double lgamma_r(double __x, int* _Nonnull __sign);
@@ -402,6 +389,8 @@ void sincosl(long double __x, long double* _Nonnull __sin, long double* _Nonnull
 #define M_2_SQRTPIl     1.128379167095512573896158903121545172L /* 2/sqrt(pi) */
 #define M_SQRT2l        1.414213562373095048801688724209698079L /* sqrt(2) */
 #define M_SQRT1_2l      0.707106781186547524400844362104849039L /* 1/sqrt(2) */
+int isinfl(long double __x) __attribute_const__;
+int isnanl(long double __x) __attribute_const__;
 #endif
 
 __END_DECLS

tests/math_test.cpp

@@ -367,9 +367,7 @@ TEST(math_h, isnan_function) {
 // Historical BSD cruft that isn't exposed in <math.h> any more.
 extern "C" int __isnan(double);
 extern "C" int __isnanf(float);
-extern "C" int isnanf(float);
 extern "C" int __isnanl(long double);
-extern "C" int isnanl(long double);
 
 TEST(math_h, __isnan) {
 #if defined(ANDROID_HOST_MUSL)