From 68d9d60a4d5a4696faf3e36a9a8a7f10ed5bdd22 Mon Sep 17 00:00:00 2001
From: "henryk@ploetzli.ch"
 <henryk@ploetzli.ch@ef4ab9da-24cd-11de-8aaa-f3a34680c41f>
Date: Wed, 25 Nov 2009 20:41:41 +0000
Subject: [PATCH] Add generic CRC calculation code

---
 armsrc/Makefile |  3 ++-
 common/crc.c    | 41 +++++++++++++++++++++++++++++++++++++++++
 include/crc.h   | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 90 insertions(+), 1 deletion(-)
 create mode 100644 common/crc.c
 create mode 100644 include/crc.h

diff --git a/armsrc/Makefile b/armsrc/Makefile
index 8010fcf0..2cfac4ac 100644
--- a/armsrc/Makefile
+++ b/armsrc/Makefile
@@ -25,7 +25,8 @@ THUMBSRC = start.c \
 ARMSRC = fpgaloader.c \
 	legicrf.c \
 	$(SRC_ISO14443a) \
-	$(SRC_ISO14443b)
+	$(SRC_ISO14443b) \
+	crc.c
 
 # Do not move this inclusion before the definition of {THUMB,ASM,ARM}SRC
 include ../common/Makefile.common
diff --git a/common/crc.c b/common/crc.c
new file mode 100644
index 00000000..817272eb
--- /dev/null
+++ b/common/crc.c
@@ -0,0 +1,41 @@
+/*
+ * crc.c
+ *
+ * Generic CRC calculation code.
+ * 
+ */
+
+#include "crc.h"
+
+void crc_init(crc_t *crc, int order, uint32_t polynom, uint32_t initial_value, uint32_t final_xor)
+{
+	crc->order = order;
+	crc->polynom = polynom;
+	crc->initial_value = initial_value;
+	crc->final_xor = final_xor;
+	crc->mask = (1L<<order)-1;
+	crc_clear(crc);
+}
+
+void crc_update(crc_t *crc, uint32_t data, int data_width)
+{
+	int i;
+	for(i=0; i<data_width; i++) {
+		int oldstate = crc->state;
+		crc->state = crc->state >> 1;
+		if( (oldstate^data) & 1 ) {
+			crc->state ^= crc->polynom;
+		}
+		data >>= 1;
+	}
+}
+
+void crc_clear(crc_t *crc)
+{
+	crc->state = crc->initial_value & crc->mask;
+}
+
+uint32_t crc_finish(crc_t *crc)
+{
+	return ( crc->state ^ crc->final_xor ) & crc->mask;
+}
diff --git a/include/crc.h b/include/crc.h
new file mode 100644
index 00000000..2ee9a4dd
--- /dev/null
+++ b/include/crc.h
@@ -0,0 +1,47 @@
+/*
+ * crc.h
+ *
+ * Generic CRC calculation code.
+ * 
+ */
+
+#ifndef CRC_H_
+#define CRC_H_
+
+#include <stdint.h>
+
+typedef struct crc {
+	uint32_t state;
+	int order;
+	uint32_t polynom;
+	uint32_t initial_value;
+	uint32_t final_xor;
+	uint32_t mask;
+} crc_t;
+
+/* Initialize a crc structure. order is the order of the polynom, e.g. 32 for a CRC-32
+ * polynom is the CRC polynom. initial_value is the initial value of a clean state.
+ * final_xor is XORed onto the state before returning it from crc_result(). */
+extern void crc_init(crc_t *crc, int order, uint32_t polynom, uint32_t initial_value, uint32_t final_xor);
+
+/* Update the crc state. data is the data of length data_width bits (only the the
+ * data_width lower-most bits are used).
+ */ 
+extern void crc_update(crc_t *crc, uint32_t data, int data_width);
+
+/* Clean the crc state, e.g. reset it to initial_value */
+extern void crc_clear(crc_t *crc);
+
+/* Get the result of the crc calculation */
+extern uint32_t crc_finish(crc_t *crc);
+
+/* Static initialization of a crc structure */
+#define CRC_INITIALIZER(_order, _polynom, _initial_value, _final_xor) { \
+	.state = ((_initial_value) & ((1L<<(_order))-1)), \
+	.order = (_order), \
+	.polynom = (_polynom), \
+	.initial_value = (_initial_value), \
+	.final_xor = (_final_xor), \
+	.mask = ((1L<<(_order))-1) }
+
+#endif /* CRC_H_ */
-- 
2.39.2