worked on FAT stuff and tests

ext/sd/fat32/UsedSpaceChecker.h

@@ -0,0 +1,25 @@
+#pragma once
+
+/**
+ * helper class to determine all clusters whice are used.
+ * starts at cluster number 2 and then iterates over all subsequent clusters
+ */
+class UsedSpaceChecker {
+
+public:
+
+	/** get the number of used clusters */
+	static uint32_t getNumUsedClusters(const FS& fs) {
+
+		uint32_t numUsed = 0;
+
+		for (ClusterNr nr = 2; nr < fs.tmp.entriesPerFAT; ++nr) {
+			ClusterNr next = fs.getNextCluster(nr);
+			if (!next.isFree()) {++numUsed;}
+		}
+
+		return numUsed;
+
+	}
+
+};