drivers: crc: Add 'pad' parameter to crc16()

'pad' parameter controls whether crc16() should add padding at the end
of input bytes or not. This allows to compute CRC16 for data stored in
non-contiguous buffers where CRC value is calculated using subsequent
calls to crc16() with padding added only for last chunk.

Signed-off-by: Andrzej Kaczmarek <[email protected]>

Author: andrzej-kaczmarek

drivers/crc/crc16_sw.c

@@ -7,13 +7,14 @@
 #include <crc16.h>
 
 u16_t crc16(const u8_t *src, size_t len, u16_t polynomial,
-	       u16_t initial_value)
+	    u16_t initial_value, bool pad)
 {
 	u16_t crc = initial_value;
+	size_t padding = pad ? sizeof(crc) : 0;
 	size_t i, b;
 
-	/* src length + crc width of zeros appended */
-	for (i = 0; i < len + sizeof(crc); i++) {
+	/* src length + padding (if required) */
+	for (i = 0; i < len + padding; i++) {
 
 		for (b = 0; b < 8; b++) {
 			u16_t divide = crc & 0x8000;

include/crc16.h

@@ -12,6 +12,7 @@
 #define __CRC16_H
 
 #include <zephyr/types.h>
+#include <stdbool.h>
 #include <stddef.h>
 
 /**
@@ -25,11 +26,12 @@
  * @param polynomial The polynomial to use omitting the leading x^16
  *        coefficient
  * @param initial_value Initial value for the CRC computation
+ * @param pad Adds padding with zeros at the end of input bytes
  *
  * @return The computed CRC16 value
  */
 u16_t crc16(const u8_t *src, size_t len, u16_t polynomial,
-	       u16_t initial_value);
+	    u16_t initial_value, bool pad);
 
 /**
  * @brief Compute CCITT variant of CRC 16
@@ -44,7 +46,7 @@ u16_t crc16(const u8_t *src, size_t len, u16_t polynomial,
  */
 static inline u16_t crc16_ccitt(const u8_t *src, size_t len)
 {
-	return crc16(src, len, 0x1021, 0xffff);
+	return crc16(src, len, 0x1021, 0xffff, true);
 }
 
 /**
@@ -60,7 +62,7 @@ static inline u16_t crc16_ccitt(const u8_t *src, size_t len)
  */
 static inline u16_t crc16_ansi(const u8_t *src, size_t len)
 {
-	return crc16(src, len, 0x8005, 0xffff);
+	return crc16(src, len, 0x8005, 0xffff, true);
 }
 
 #endif