diff -r 93272c0f9a80 -r 63e6243b880c updaterevision/updaterevision.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/updaterevision/updaterevision.c	Thu Feb 06 20:43:22 2014 +0200
@@ -0,0 +1,136 @@
+/* updaterevision.c
+ *
+ * Public domain. This program uses git commands command to get
+ * various bits of repository status for a particular directory
+ * and writes it into a header file so that it can be used for a
+ * project's versioning.
+ */
+
+#define _CRT_SECURE_NO_DEPRECATE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+#include <errno.h>
+
+#ifdef _WIN32
+#define popen _popen
+#define pclose _pclose
+#endif
+
+// Used to strip newline characters from lines read by fgets.
+void stripnl(char *str)
+{
+	if (*str != '\0')
+	{
+		size_t len = strlen(str);
+		if (str[len - 1] == '\n')
+		{
+			str[len - 1] = '\0';
+		}
+	}
+}
+
+int main(int argc, char **argv)
+{
+	char vertag[64], lastlog[64], lasthash[64], *hash = NULL;
+	FILE *stream = NULL;
+	int gotrev = 0, needupdate = 1;
+
+	vertag[0] = '\0';
+	lastlog[0] = '\0';
+
+	if (argc != 2)
+	{
+		fprintf(stderr, "Usage: %s <path to gitinfo.h>\n", argv[0]);
+		return 1;
+	}
+
+	// Use git describe --tags to get a version string. If we are sitting directly
+	// on a tag, it returns that tag. Otherwise it returns <most recent tag>-<number of
+	// commits since the tag>-<short hash>.
+	// Use git log to get the time of the latest commit in ISO 8601 format and its full hash.
+	stream = popen("git describe --tags && git log -1 --format=%ai*%H", "r");
+
+	if (NULL != stream)
+	{
+		if (fgets(vertag, sizeof vertag, stream) == vertag &&
+			fgets(lastlog, sizeof lastlog, stream) == lastlog)
+		{
+			stripnl(vertag);
+			stripnl(lastlog);
+			gotrev = 1;
+		}
+
+		pclose(stream);
+	}
+
+	if (gotrev)
+	{
+		hash = strchr(lastlog, '*');
+		if (hash != NULL)
+		{
+			*hash = '\0';
+			hash++;
+		}
+	}
+	if (hash == NULL)
+	{
+		fprintf(stderr, "Failed to get commit info: %s\n", strerror(errno));
+		strcpy(vertag, "<unknown version>");
+		lastlog[0] = '\0';
+		lastlog[1] = '0';
+		lastlog[2] = '\0';
+		hash = lastlog + 1;
+	}
+
+	stream = fopen (argv[1], "r");
+	if (stream != NULL)
+	{
+		if (!gotrev)
+		{ // If we didn't get a revision but the file does exist, leave it alone.
+			fclose (stream);
+			return 0;
+		}
+		// Read the revision that's in this file already. If it's the same as
+		// what we've got, then we don't need to modify it and can avoid rebuilding
+		// dependant files.
+		if (fgets(lasthash, sizeof lasthash, stream) == lasthash)
+		{
+			stripnl(lasthash);
+			if (strcmp(hash, lasthash + 3) == 0)
+			{
+				needupdate = 0;
+			}
+		}
+		fclose (stream);
+	}
+
+	if (needupdate)
+	{
+		stream = fopen (argv[1], "w");
+		if (stream == NULL)
+		{
+			return 1;
+		}
+		fprintf(stream,
+"// %s\n"
+"//\n"
+"// This file was automatically generated by the\n"
+"// updaterevision tool. Do not edit by hand.\n"
+"\n"
+"#define GIT_DESCRIPTION \"%s\"\n"
+"#define GIT_HASH \"%s\"\n"
+"#define GIT_TIME \"%s\"\n",
+			hash, vertag, hash, lastlog);
+		fclose(stream);
+		fprintf(stderr, "%s updated to commit %s.\n", argv[1], vertag);
+	}
+	else
+	{
+		fprintf (stderr, "%s is up to date at commit %s.\n", argv[1], vertag);
+	}
+
+	return 0;
+}