sys/checksum: initial import including CRC16-CCITT

Adds a checksum module which includes an implementation "the CCITT"
variant of the CRC16 algorithm.

sys/checksum/Makefile

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+include $(RIOTBASE)/Makefile.base

sys/checksum/crc16_ccitt.c

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+/*
+ * Copyright 2016 Ludwig Knüpfer <ludwig.knuepfer@fu-berlin.de>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     sys_checksum_crc16_ccitt
+ * @{
+ *
+ * @file
+ * @brief       CRC16 implementation
+ *
+ * @author      Ludwig Knüpfer <ludwig.knuepfer@fu-berlin.de>
+ *
+ * @}
+ */
+
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "checksum/crc16_ccitt.h"
+
+static const uint16_t _crc16_lookuptable[256] = {
+    0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
+    0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
+    0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
+    0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de,
+    0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
+    0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
+    0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
+    0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc,
+    0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
+    0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
+    0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12,
+    0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
+    0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41,
+    0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49,
+    0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
+    0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78,
+    0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
+    0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
+    0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e,
+    0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
+    0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
+    0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
+    0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c,
+    0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
+    0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
+    0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3,
+    0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
+    0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92,
+    0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9,
+    0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
+    0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
+    0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0
+};
+
+uint16_t crc16_ccitt_update(uint16_t crc, const unsigned char *buf, size_t len)
+{
+    while (len--) {
+        crc = ((crc << 8) ^ _crc16_lookuptable[((crc >> 8) ^ ((*buf++) & 0x00FF))]);
+    }
+
+    return crc;
+}
+
+uint16_t crc16_ccitt_calc(const unsigned char *buf, size_t len)
+{
+    return crc16_ccitt_update(0x1D0F, buf, len);
+}

sys/include/checksum/crc16_ccitt.h

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+/*
+ * Copyright 2016 Ludwig Knüpfer <ludwig.knuepfer@fu-berlin.de>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @defgroup    sys_checksum_crc16_ccitt CRC16-CCITT
+ * @ingroup     sys_checksum
+ *
+ * @brief       CRC16-CCITT checksum algorithm
+ * @details     This implementation of CRC16 is based on the CCITT
+ *              specification using 0x1D0F as a start value.
+ *              Using a different start value is possible by calling
+ *              crc16_ccitt_update() with the desired start value
+ *              instead of crc16_ccitt_calc().
+ *
+ * @{
+ * @file
+ * @author      Ludwig Knüpfer <ludwig.knuepfer@fu-berlin.de>
+ */
+
+#ifndef CRC16_CCITT_H
+#define CRC16_CCITT_H
+
+#include <stdint.h>
+#include <stdlib.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief           Update CRC16-CCITT
+ *
+ * @param[in]  crc  A start value for the CRC calculation, usually the
+ *                  return value of a previous call to
+ *                  crc16_ccitt_calc() or crc16_ccitt_update()
+ * @param[in]  buf  Start of the memory area to checksum
+ * @param[in]  len  Number of bytes to checksum
+ *
+ * @return          Checksum of the specified memory area based on the
+ *                  given start value
+ */
+uint16_t crc16_ccitt_update(uint16_t crc, const unsigned char *buf, size_t len);
+
+/**
+ * @brief           Calculate CRC16-CCITT
+ *
+ * @param[in]  buf  Start of the memory area to checksum
+ * @param[in]  len  Number of bytes to checksum
+ *
+ * @return          Checksum of the specified memory area
+ */
+uint16_t crc16_ccitt_calc(const unsigned char *buf, size_t len);
+
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* CRC16_CCITT_H */
+
+/** @} */

sys/include/checksum/doc.txt

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+/*
+ * Copyright 2016 Ludwig Knüpfer <ludwig.knuepfer@fu-berlin.de>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @defgroup    sys_checksum Checksum
+ * @ingroup     sys
+ * @brief       Checksum function libraries
+ */