Added logging facilities

Makefile.am

@@ -28,6 +28,7 @@ subdirinclude_HEADERS = \
 	include/criterion/criterion.h \
 	include/criterion/event.h \
 	include/criterion/hooks.h \
+	include/criterion/logging.h \
 	include/criterion/stats.h
 
 libcriterion_la_SOURCES = \
@@ -41,4 +42,5 @@ libcriterion_la_SOURCES = \
 	src/process.h \
 	src/stats.c \
 	src/stats.h \
+	src/logging.c \
 	src/main.c

include/criterion/common.h

@@ -27,4 +27,10 @@
 # define SECTION_(Name) __attribute__((section(Name)))
 # define UNUSED __attribute__((unused))
 
+# ifdef __GNUC__
+#  define FORMAT(Archetype, Index, Ftc) __attribute__((format(Archetype, Index, Ftc)))
+# else
+#  define FORMAT(Archetype, Index, Ftc)
+# endif
+
 #endif /* !CRITERION_COMMON_H_ */

include/criterion/logging.h

@@ -0,0 +1,19 @@
+#ifndef CRITERION_LOGGING_H_
+# define CRITERION_LOGGING_H_
+
+#include "common.h"
+
+enum criterion_logging_level {
+    CRITERION_INFO = 1,
+    CRITERION_IMPORTANT,
+};
+
+extern enum criterion_logging_level logging_threshold;
+
+FORMAT(printf, 2, 3)
+void criterion_log(enum criterion_logging_level level, const char *msg, ...);
+
+# define criterion_info(...) criterion_log(CRITERION_INFO, __VA_ARGS__)
+# define criterion_important(...) criterion_log(CRITERION_IMPORTANT, __VA_ARGS__)
+
+#endif /* !CRITERION_LOGGING_H_ */

src/logging.c

@@ -0,0 +1,16 @@
+#include <stdio.h>
+#include <stdarg.h>
+#include "criterion/logging.h"
+
+enum criterion_logging_level logging_threshold = CRITERION_IMPORTANT;
+
+void criterion_log(enum criterion_logging_level level, const char *msg, ...) {
+    va_list args;
+
+    if (level < logging_threshold)
+        return;
+
+    va_start(args, msg);
+    vfprintf(stderr, msg, args);
+    va_end(args);
+}