Check for isnan() and isinf() by linking

configure.ac

@@ -43,6 +43,37 @@ case "$ac_cv_header_locale_h$ac_cv_func_localeconv" in
 esac
 AC_SUBST([json_have_localeconv])
 
+# isinf/isnan
+AC_MSG_CHECKING([whether isnan and isinf are defined and/or need -lm])
+AC_LANG([C])
+
+# First, test without -lm
+isnan_isinf_found=no
+AC_LINK_IFELSE(
+    [AC_LANG_PROGRAM([#include <math.h>], [isnan(0.1); isinf(0.1);])],
+    [AC_MSG_RESULT([defined, -lm not needed]); isnan_isinf_found=yes]
+)
+
+if test "x$isnan_isinf_found" = "xno"; then
+    # Not found, test with -lm
+    libs_before_test=$LIBS
+    LIBS="$LIBS -lm"
+    AC_LINK_IFELSE(
+        [AC_LANG_PROGRAM([#include <math.h>], [isnan(0.1); isinf(0.1);])],
+        [AC_MSG_RESULT([defined, -lm needed]); isnan_isinf_found=yes],
+        [LIBS=$libs_before_test]
+    )
+fi
+
+if test "x$isnan_isinf_found" = "xno"; then
+    # Still not found
+    AC_MSG_RESULT([not defined])
+    json_have_isnan_isinf=0
+else
+    json_have_isnan_isinf=1
+fi
+AC_SUBST([json_have_isnan_isinf])
+
 AC_CONFIG_FILES([
         jansson.pc
         Makefile

jansson.pc.in

@@ -7,4 +7,5 @@ Name: Jansson
 Description: Library for encoding, decoding and manipulating JSON data
 Version: @VERSION@
 Libs: -L${libdir} -ljansson
+Libs.private: @LIBS@
 Cflags: -I${includedir}

src/jansson_config.h.in

@@ -36,4 +36,9 @@
    otherwise to 0. */
 #define JSON_HAVE_LOCALECONV @json_have_localeconv@
 
+/* If isnan() and isinf() are available in math.h, define to 1,
+   otherwise to 0. Note that you may need to link with -lm on some
+   systems. */
+#define JSON_HAVE_ISNAN_ISINF @json_have_isnan_isinf@
+
 #endif

src/value.c

@@ -19,11 +19,12 @@
 #include "jansson_private.h"
 #include "utf.h"
 
-/* Work around nonstandard isnan() and isinf() implementations */
-#ifndef isnan
+/* Work around missing isnan() and isinf() implementations */
+#if !JSON_HAVE_ISNAN_ISINF
+/* Undef them just to be sure */
+#undef isnan
+#undef isinf
 static JSON_INLINE int isnan(double x) { return x != x; }
-#endif
-#ifndef isinf
 static JSON_INLINE int isinf(double x) { return !isnan(x) && isnan(x - x); }
 #endif
 

win32/jansson_config.h

@@ -36,4 +36,9 @@
    otherwise to 0. */
 #define JSON_HAVE_LOCALECONV 1
 
+/* If isnan() and isinf() are available in math.h, define to 1,
+   otherwise to 0. Note that you may need to link with -lm on some
+   systems. */
+#define JSON_HAVE_ISNAN_ISINF 1
+
 #endif