From bd75219ba00ca0f41be773c3dbbf5fa0bff0d908 Mon Sep 17 00:00:00 2001
From: Patrik Flykt <patrik.flykt@intel.com>
Date: Thu, 30 Mar 2017 12:54:29 +0300
Subject: [PATCH] crc16: Create function for computing CRC 16

Add the simplest possible CRC 16 function that computes the CRC value
without the help of lookup tables.

Change-Id: I9163389adaa4a70c4e8ce8ce6d5f0661f40c7871
Signed-off-by: Patrik Flykt <patrik.flykt@intel.com>
---
 drivers/Makefile       |  1 +
 drivers/crc/Makefile   |  1 +
 drivers/crc/crc16_sw.c | 35 ++++++++++++++++++++++
 include/crc16.h        | 66 ++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 103 insertions(+)
 create mode 100644 drivers/crc/Makefile
 create mode 100644 drivers/crc/crc16_sw.c
 create mode 100644 include/crc16.h

diff --git a/drivers/Makefile b/drivers/Makefile
index 4bf578b86c4..8fe8bbcfefe 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -30,3 +30,4 @@ obj-$(CONFIG_PINMUX) += pinmux/
 obj-$(CONFIG_DMA) += dma/
 obj-$(CONFIG_USB) += usb/
 obj-$(CONFIG_CRYPTO) += crypto/
+obj-y += crc/
diff --git a/drivers/crc/Makefile b/drivers/crc/Makefile
new file mode 100644
index 00000000000..9968597cc2e
--- /dev/null
+++ b/drivers/crc/Makefile
@@ -0,0 +1 @@
+obj-y += crc16_sw.o
diff --git a/drivers/crc/crc16_sw.c b/drivers/crc/crc16_sw.c
new file mode 100644
index 00000000000..ee9da073bb9
--- /dev/null
+++ b/drivers/crc/crc16_sw.c
@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2017 Intel Corporation.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <crc16.h>
+
+uint16_t crc16(const uint8_t *src, size_t len, uint16_t polynomial,
+	       uint16_t initial_value)
+{
+	uint16_t crc = initial_value;
+	size_t i, b;
+
+	/* src length + crc width of zeros appended */
+	for (i = 0; i < len + sizeof(crc); i++) {
+
+		for (b = 0; b < 8; b++) {
+			uint16_t divide = crc & 0x8000;
+
+			crc = (crc << 1);
+
+			/* choose input bytes or implicit trailing zeros */
+			if (i < len) {
+				crc |= !!(src[i] & (0x80 >> b));
+			}
+
+			if (divide) {
+				crc = crc ^ polynomial;
+			}
+		}
+	}
+
+	return crc;
+}
diff --git a/include/crc16.h b/include/crc16.h
new file mode 100644
index 00000000000..cd29b130aa7
--- /dev/null
+++ b/include/crc16.h
@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2017 Intel Corporation.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/** @file
+ * @brief CRC 16 computation function
+ */
+
+#ifndef __CRC16_H
+#define __CRC16_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+/**
+ * @brief Generic function for computing CRC 16
+ *
+ * Compute CRC 16 by passing in the address of the input, the input length
+ * and polynomial used in addition to the initial value.
+ *
+ * @param src Input bytes for the computation
+ * @param len Length of the input in bytes
+ * @param polynomial The polynomial to use omitting the leading x^16
+ *        coefficient
+ * @param initial_value Initial value for the CRC computation
+ *
+ * @return The computed CRC16 value
+ */
+uint16_t crc16(const uint8_t *src, size_t len, uint16_t polynomial,
+	       uint16_t initial_value);
+
+/**
+ * @brief Compute CCITT variant of CRC 16
+ *
+ * CCITT variant of CRC 16 is using 0x1021 as its polynomial with the initial
+ * value set to 0xffff.
+ *
+ * @param src Input bytes for the computation
+ * @param len Length of the input in bytes
+ *
+ * @return The computed CRC16 value
+ */
+static inline uint16_t crc16_ccitt(const uint8_t *src, size_t len)
+{
+	return crc16(src, len, 0x1021, 0xffff);
+}
+
+/**
+ * @brief Compute ANSI variant of CRC 16
+ *
+ * ANSI variant of CRC 16 is using 0x8005 as its polynomial with the initial
+ * value set to 0xffff.
+ *
+ * @param src Input bytes for the computation
+ * @param len Length of the input in bytes
+ *
+ * @return The computed CRC16 value
+ */
+static inline uint16_t crc16_ansi(const uint8_t *src, size_t len)
+{
+	return crc16(src, len, 0x8005, 0xffff);
+}
+
+#endif