1 files changed, 140 insertions, 0 deletions
diff --git a/src/prbs.c b/src/prbs.c
new file mode 100644
index 0000000..8a11266
--- /dev/null
+++ b/src/prbs.c
@@ -0,0 +1,140 @@
+/*
+   Copyright (C) 2005, 2006, 2007, 2008, 2009 Her Majesty the Queen in Right
+   of Canada (Communications Research Center Canada)
+   */
+/*
+   This file is part of CRC-DabMux.
+
+   CRC-DabMux 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 3 of the
+   License, or (at your option) any later version.
+
+   CRC-DabMux 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 CRC-DabMux.  If not, see <http://www.gnu.org/licenses/>.
+   */
+
+#include "prbs.h"
+
+#include <string.h>
+#include <stdlib.h>
+#include <limits.h>
+
+
+/*
+ * Generate a parity check for a 32-bit word.
+ */
+unsigned long parity_check(unsigned long prbs_accum)
+{
+    unsigned long mask=1UL, parity=0UL;
+    int i;
+    for (i = 0;  i < 32;  ++i) {
+        parity ^= ((prbs_accum & mask) != 0UL);
+        mask <<= 1;
+    }
+    return parity;
+}
+
+/*
+ * Generate a table of matrix products to update a 32-bit PRBS generator.
+ */
+void gen_prbs_table(void* args)
+{
+    prbs_data* data = (prbs_data*)args;
+    int i;
+    for (i = 0;  i < 4;  ++i) {
+        int j;
+        for (j = 0;  j < 256;  ++j) {
+            unsigned long prbs_accum = ((unsigned long)j << (i * 8));
+            int k;
+            for (k = 0;  k < 8;  ++k) {
+                prbs_accum = (prbs_accum << 1)
+                                ^ parity_check(prbs_accum & data->polynomial);
+            }
+            data->prbs_table[i][j] = (prbs_accum & 0xff);
+        }
+    }
+}
+
+/*
+ * Update a 32-bit PRBS generator eight bits at a time.
+ */
+unsigned long update_prbs(void* args)
+{
+    prbs_data* data = (prbs_data*)args;
+    unsigned char acc_lsb = 0;
+    int i;
+    for (i = 0;  i < 4;  ++i ) {
+        acc_lsb ^= data->prbs_table [i] [ (data->accum >> (i * 8) ) & 0xff ];
+    }
+    return (data->accum << 8) ^ ((unsigned long)acc_lsb);
+}
+
+/*
+ * Generate the weight table.
+ */
+void gen_weight_table(void* args)
+{
+    prbs_data* data = (prbs_data*)args; 
+    int i;
+    for (i = 0;  i < 256;  ++i) {
+        unsigned char mask=1U, ones_count = 0U;
+        int j;
+        for (j = 0;  j < 8;  ++j) {
+            ones_count += ((i & mask) != 0U);
+            mask = mask << 1;
+        }
+        data->weight[i] = ones_count;
+    }
+}
+
+/*
+ * Count the number of errors in a block of received data.
+ */
+unsigned long error_count(void* args, unsigned char *rx_data,
+        int rx_data_length)
+{
+    prbs_data* data = (prbs_data*)args;
+    unsigned long error_count = 0U;
+    unsigned long prbs_accum = 0U;
+    int i;
+
+    /* seed the PRBS accumulator */
+    for (i = 0;  i < 4;  ++i) {
+        prbs_accum = (prbs_accum << 8) ^ (rx_data[i] ^ data->polarity_mask);
+    }
+
+    /* check the received data */
+    for (i = 0;  i < rx_data_length;  ++i) {
+        unsigned char error_pattern = (unsigned char)
+                          ((prbs_accum >> 24)
+                          ^ (rx_data[i] ^ data->polarity_mask));
+        if (error_pattern != 0U) {
+            error_count += data->weight[error_pattern];
+        }
+        prbs_accum = update_prbs(data);
+    }
+    return error_count;
+}
+
+void gen_sequence(void* args, unsigned char *tx_data, int tx_data_length,
+        unsigned long polynomial)
+{
+    prbs_data* data = (prbs_data*)args;
+    unsigned long prbs_accum = 0U;
+
+    while (prbs_accum < polynomial) {
+        prbs_accum <<= 1;
+        prbs_accum |= 1;
+    }
+
+    while (tx_data_length-- > 0) {
+        prbs_accum = update_prbs(data);
+        *(tx_data++) = (unsigned char)(prbs_accum & 0xff);
+    }
+}