Fix for bug #28240: "isinf()" cannot be used in C++ for lack of prototype

- Since isinf() portability across various platforms and
  compilers is a complicated question, we should not use
  it directly. Instead, the my_isinf() macro should be used,
  which is defined as an alias to the system-defined isinf()
  if it is safe to use, or a workaround implementation otherwise


configure.in:
  Added a check to define HAVE_ISINF only if it can be used
  in C++ code as well.
include/my_global.h:
  Define my_isinf() as an alias to isinf(), if it is available
  in both C and C++ code. Otherwise, define it to a workaround
  implementation.
sql/item_func.cc:
  Replaced isinf() with my_isinf().
strings/strtod.c:
  Replaced isinf() with my_isinf().

configure.in

@@ -2006,12 +2006,20 @@ case "$target" in
     ;;
 esac
 
-# isinf() could be a function or a macro (HPUX)
-AC_MSG_CHECKING(for isinf with <math.h>)
+# Check that isinf() is available in math.h and can be used in both C and C++ 
+# code
+AC_MSG_CHECKING(for isinf in <math.h>)
 AC_TRY_LINK([#include <math.h>], [float f = 0.0; int r = isinf(f); return r],
+  AC_MSG_RESULT(yes)
+  AC_MSG_CHECKING(whether isinf() can be used in C++ code)
+  AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  AC_TRY_LINK([#include <math.h>], [float f = 0.0; int r = isinf(f); return r],
     AC_MSG_RESULT(yes)
     AC_DEFINE(HAVE_ISINF, [1], [isinf() macro or function]),
     AC_MSG_RESULT(no))
+  AC_LANG_RESTORE,
+  AC_MSG_RESULT(no))
  
 CFLAGS="$ORG_CFLAGS"
 

include/my_global.h

@@ -792,12 +792,11 @@ typedef SOCKET_SIZE_TYPE size_socket;
 #define isnan(x) ((x) != (x))
 #endif
 
-#if !defined(HAVE_ISINF)
-/* The configure check for "isinf with math.h" has failed */
-#ifdef isinf
-#undef isinf
-#endif
-#define isinf(X) (!finite(X) && !isnan(X))
+#ifdef HAVE_ISINF
+/* isinf() can be used in both C and C++ code */
+#define my_isinf(X) isinf(X)
+#else
+#define my_isinf(X) (!finite(X) && !isnan(X))
 #endif
 
 /* Define missing math constants. */

sql/item_func.cc

@@ -1980,9 +1980,9 @@ double my_double_round(double value, longlong dec, bool dec_unsigned,
   tmp=(abs_dec < array_elements(log_10) ?
        log_10[abs_dec] : pow(10.0,(double) abs_dec));
 
-  if (dec_negative && isinf(tmp))
+  if (dec_negative && my_isinf(tmp))
     tmp2= 0;
-  else if (!dec_negative && isinf(value * tmp))
+  else if (!dec_negative && my_isinf(value * tmp))
     tmp2= value;
   else if (truncate)
   {

strings/strtod.c

@@ -194,7 +194,7 @@ double my_strtod(const char *str, char **end_ptr, int *error)
 done:
   *end_ptr= (char*) str;                        /* end of number */
 
-  if (overflow || isinf(result))
+  if (overflow || my_isinf(result))
   {
     result= DBL_MAX;
     *error= EOVERFLOW;