1 files changed, 120 insertions, 0 deletions
diff --git a/lib/decoding/osmocom/core/crc16gen.c b/lib/decoding/osmocom/core/crc16gen.c
new file mode 100644
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--- /dev/null
+++ b/lib/decoding/osmocom/core/crc16gen.c
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+/*
+ * crc16gen.c
+ *
+ * Generic CRC routines (for max 16 bits poly)
+ *
+ * Copyright (C) 2011  Sylvain Munaut <tnt@246tNt.com>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/*! \addtogroup crcgen
+ *  @{
+ */
+
+/*! \file crc16gen.c
+ * Osmocom generic CRC routines (for max 16 bits poly)
+ */
+
+#include <stdint.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/crc16gen.h>
+
+
+/*! \brief Compute the CRC value of a given array of hard-bits
+ *  \param[in] code The CRC code description to apply
+ *  \param[in] in Array of hard bits
+ *  \param[in] len Length of the array of hard bits
+ *  \returns The CRC value
+ */
+uint16_t
+osmo_crc16gen_compute_bits(const struct osmo_crc16gen_code *code,
+                           const ubit_t *in, int len)
+{
+	const uint16_t poly = code->poly;
+	uint16_t crc = code->init;
+	int i, n = code->bits-1;
+
+	for (i=0; i<len; i++) {
+		uint16_t bit = in[i] & 1;
+		crc ^= (bit << n);
+		if (crc & ((uint16_t)1 << n)) {
+			crc <<= 1;
+			crc ^= poly;
+		} else {
+			crc <<= 1;
+		}
+		crc &= ((uint16_t)1 << code->bits) - 1;
+	}
+
+	crc ^= code->remainder;
+
+	return crc;
+}
+
+
+/*! \brief Checks the CRC value of a given array of hard-bits
+ *  \param[in] code The CRC code description to apply
+ *  \param[in] in Array of hard bits
+ *  \param[in] len Length of the array of hard bits
+ *  \param[in] crc_bits Array of hard bits with the alleged CRC
+ *  \returns 0 if CRC matches. 1 in case of error.
+ *
+ * The crc_bits array must have a length of code->len
+ */
+int
+osmo_crc16gen_check_bits(const struct osmo_crc16gen_code *code,
+                         const ubit_t *in, int len, const ubit_t *crc_bits)
+{
+	uint16_t crc;
+	int i;
+
+	crc = osmo_crc16gen_compute_bits(code, in, len);
+
+	for (i=0; i<code->bits; i++)
+		if (crc_bits[i] ^ ((crc >> (code->bits-i-1)) & 1))
+			return 1;
+
+	return 0;
+}
+
+
+/*! \brief Computes and writes the CRC value of a given array of bits
+ *  \param[in] code The CRC code description to apply
+ *  \param[in] in Array of hard bits
+ *  \param[in] len Length of the array of hard bits
+ *  \param[in] crc_bits Array of hard bits to write the computed CRC to
+ *
+ * The crc_bits array must have a length of code->len
+ */
+void
+osmo_crc16gen_set_bits(const struct osmo_crc16gen_code *code,
+                       const ubit_t *in, int len, ubit_t *crc_bits)
+{
+	uint16_t crc;
+	int i;
+
+	crc = osmo_crc16gen_compute_bits(code, in, len);
+
+	for (i=0; i<code->bits; i++)
+		crc_bits[i] = ((crc >> (code->bits-i-1)) & 1);
+}
+
+/*! @} */
+
+/* vim: set syntax=c: */