1 files changed, 41 insertions, 0 deletions
diff --git a/rfid_iso14443_common.c b/rfid_iso14443_common.c
new file mode 100644
index 0000000..aacb45d
--- /dev/null
+++ b/rfid_iso14443_common.c
@@ -0,0 +1,41 @@
+static unsigned int fsdi_table[] = { 16, 24, 32, 40, 48, 64, 96, 128, 256 };
+
+int iso14443_fsdi_to_fsd(unsigned int *fsd, unsigned char fsdi)
+{
+	/* ISO 14443-4:2000(E) Section 5.1. */
+	if (fsdi > sizeof(fsdi_table)/sizeof(unsigned int))
+		return -1;
+
+	*fsd = fsdi_table[fsdi];
+	return 0;
+}
+
+int iso14443_fsd_to_fsdi(unsigned char *fsdi, unsigned int fsd)
+{
+	int i;
+
+	for (i = 0; i < sizeof(fsdi_table)/sizeof(unsigned int); i++) {
+		if (fsdi_table[i] == fsd) {
+			*fsdi = i;
+			return 0;
+		}
+	}
+
+	return -1;
+}
+
+/* calculate the fsd that is equal or the closest smaller value
+ * that can be coded as fsd */
+unsigned int iso14443_fsd_approx(unsigned int fsd)
+{
+	unsigned int tbl_size = sizeof(fsdi_table)/sizeof(unsigned int);
+	int i;
+
+	for (i = tbl_size-1; i >= 0; i--) {
+		if (fsdi_table[i] <= fsd)
+			return fsdi_table[i];
+	}
+	/* not reached: return smallest possible FSD */
+	return fsdi_table[0];
+}
+