From: Andreas Sandberg <redacted>
Date: Fri, 6 Mar 2020 14:38:19 +0000 (+0000)
Subject: crc: Factor out CRC16 implementation from Modbus
X-Git-Url: https://sigrok.org/gitweb/?p=libsigrok.git;a=commitdiff_plain;h=4ea012bdf543a0daff4acf4bdc27caff514903e8

crc: Factor out CRC16 implementation from Modbus

Being able to calculate a CRC16 is useful in multiple places, factor
this into a new module with CRC implementation. This module currently
only supports ANSI/Modbus/USB flavor of CRC16.

Signed-off-by: Andreas Sandberg <redacted>
---

diff --git a/Makefile.am b/Makefile.am
index 31e4fba0..8eb3d7a5 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -52,6 +52,7 @@ libsigrok_la_SOURCES = \
 	src/backend.c \
 	src/binary_helpers.c \
 	src/conversion.c \
+	src/crc.c \
 	src/device.c \
 	src/session.c \
 	src/session_file.c \
diff --git a/src/libsigrok-internal.h b/src/libsigrok-internal.h
index 990d038f..0d18bee4 100644
--- a/src/libsigrok-internal.h
+++ b/src/libsigrok-internal.h
@@ -1783,6 +1783,22 @@ SR_PRIV int bv_get_value(float *out, const struct binary_value_spec *spec, const
 SR_PRIV int bv_send_analog_channel(const struct sr_dev_inst *sdi, struct sr_channel *ch,
 				   const struct binary_analog_channel *spec, const void *data, size_t length);
 
+/*--- crc.c -----------------------------------------------------------------*/
+
+#define SR_CRC16_DEFAULT_INIT 0xffffU
+
+/**
+ * Calculate a CRC16 checksum using the 0x8005 polynomial.
+ *
+ * This CRC16 flavor is also known as CRC16-ANSI or CRC16-MODBUS.
+ *
+ * @param crc Initial value (typically 0xffff)
+ * @param buffer Input buffer
+ * @param len Buffer length
+ * @return Checksum
+ */
+SR_PRIV uint16_t sr_crc16(uint16_t crc, const uint8_t *buffer, int len);
+
 /*--- modbus/modbus.c -------------------------------------------------------*/
 
 struct sr_modbus_dev_inst {
diff --git a/src/modbus/modbus_serial_rtu.c b/src/modbus/modbus_serial_rtu.c
index f7fee0ab..8d6978b1 100644
--- a/src/modbus/modbus_serial_rtu.c
+++ b/src/modbus/modbus_serial_rtu.c
@@ -81,27 +81,6 @@ static int modbus_serial_rtu_source_remove(struct sr_session *session,
 	return serial_source_remove(session, serial);
 }
 
-static uint16_t modbus_serial_rtu_crc(uint16_t crc,
-		const uint8_t *buffer, int len)
-{
-	int i;
-
-	if (!buffer || len < 0)
-		return crc;
-
-	while (len--) {
-		crc ^= *buffer++;
-		for (i = 0; i < 8; i++) {
-			int carry = crc & 1;
-			crc >>= 1;
-			if (carry)
-				crc ^= 0xA001;
-		}
-	}
-
-	return crc;
-}
-
 static int modbus_serial_rtu_send(void *priv,
 		const uint8_t *buffer, int buffer_size)
 {
@@ -119,8 +98,8 @@ static int modbus_serial_rtu_send(void *priv,
 	if (result < 0)
 		return SR_ERR;
 
-	crc = modbus_serial_rtu_crc(0xFFFF, &slave_addr, sizeof(slave_addr));
-	crc = modbus_serial_rtu_crc(crc, buffer, buffer_size);
+	crc = sr_crc16(SR_CRC16_DEFAULT_INIT, &slave_addr, sizeof(slave_addr));
+	crc = sr_crc16(crc, buffer, buffer_size);
 
 	result = serial_write_blocking(serial, &crc, sizeof(crc), 0);
 	if (result < 0)
@@ -143,8 +122,8 @@ static int modbus_serial_rtu_read_begin(void *priv, uint8_t *function_code)
 	if (ret != 1)
 		return SR_ERR;
 
-	modbus->crc = modbus_serial_rtu_crc(0xFFFF, &slave_addr, sizeof(slave_addr));
-	modbus->crc = modbus_serial_rtu_crc(modbus->crc, function_code, 1);
+	modbus->crc = sr_crc16(SR_CRC16_DEFAULT_INIT, &slave_addr, sizeof(slave_addr));
+	modbus->crc = sr_crc16(modbus->crc, function_code, 1);
 
 	return SR_OK;
 }
@@ -157,7 +136,7 @@ static int modbus_serial_rtu_read_data(void *priv, uint8_t *buf, int maxlen)
 	ret = serial_read_nonblocking(modbus->serial, buf, maxlen);
 	if (ret < 0)
 		return ret;
-	modbus->crc = modbus_serial_rtu_crc(modbus->crc, buf, ret);
+	modbus->crc = sr_crc16(modbus->crc, buf, ret);
 	return ret;
 }