From 5fc3f95ee0bc30ab62e9a3fffec06fc5e5fc5f96 Mon Sep 17 00:00:00 2001
From: Jan Mrna <mj370@protonmail.com>
Date: Sun, 12 Jun 2022 22:25:57 +0200
Subject: [PATCH] Added crc files

---
 crc8.c | 31 +++++++++++++++++++++++++++++++
 crc8.h | 22 ++++++++++++++++++++++
 2 files changed, 53 insertions(+)
 create mode 100644 crc8.c
 create mode 100644 crc8.h

diff --git a/crc8.c b/crc8.c
new file mode 100644
index 0000000..a8ed0f3
--- /dev/null
+++ b/crc8.c
@@ -0,0 +1,31 @@
+/*
+ * crc.c
+ *
+ *  Created on: Jun 9, 2021
+ *      Author: user
+ */
+
+#include "crc8.h"
+
+/* TODO add polynomial and init value to make this function
+ * generic */
+
+/* Stolen from Sensirion SCD4x datasheet, section 3.11 */
+uint8_t crc8_calculate(const uint8_t *data, uint16_t count)
+{
+	uint16_t current_byte;
+	uint8_t crc = CRC8_INIT;
+	uint8_t crc_bit;
+	/* calculates 8-Bit checksum with given polynomial */
+	for (current_byte = 0; current_byte < count; ++current_byte) {
+		crc ^= (data[current_byte]);
+		for(crc_bit = 8; crc_bit > 0; --crc_bit) {
+			if (crc & 0x80) {
+				crc =(crc << 1) ^ CRC8_POLYNOMIAL;
+			} else {
+				crc = (crc << 1);
+			}
+		}
+	}
+	return crc;
+}
diff --git a/crc8.h b/crc8.h
new file mode 100644
index 0000000..6820352
--- /dev/null
+++ b/crc8.h
@@ -0,0 +1,22 @@
+/*
+ * crc.h
+ *
+ *  Created on: Jun 9, 2021
+ *      Author: user
+ */
+
+#ifndef INC_CRC8_H_
+#define INC_CRC8_H_
+
+#include "stdint.h"
+
+/*
+ * Definitions & macros
+ */
+
+#define CRC8_POLYNOMIAL ((uint8_t)0x31)
+#define CRC8_INIT ((uint8_t)0xFF)
+
+uint8_t crc8_calculate(const uint8_t *data, uint16_t count);
+
+#endif /* INC_CRC8_H_ */