Bugfix + added M17 decoder to the linux CI

core/libcorrect/src/convolutional/lookup.c

@@ -0,0 +1,74 @@
+#include "correct/convolutional/lookup.h"
+
+// table has numstates rows
+// each row contains all of the polynomial output bits concatenated together
+// e.g. for rate 2, we have 2 bits in each row
+// the first poly gets the LEAST significant bit, last poly gets most significant
+void fill_table(unsigned int rate,
+                unsigned int order,
+                const polynomial_t *poly,
+                unsigned int *table) {
+    for (shift_register_t i = 0; i < 1 << order; i++) {
+        unsigned int out = 0;
+        unsigned int mask = 1;
+        for (size_t j = 0; j < rate; j++) {
+            out |= (popcount(i & poly[j]) % 2) ? mask : 0;
+            mask <<= 1;
+        }
+        table[i] = out;
+    }
+}
+
+pair_lookup_t pair_lookup_create(unsigned int rate,
+                                 unsigned int order,
+                                 const unsigned int *table) {
+    pair_lookup_t pairs;
+
+    pairs.keys = malloc(sizeof(unsigned int) * (1 << (order - 1)));
+    pairs.outputs = calloc((1 << (rate * 2)), sizeof(unsigned int));
+    unsigned int *inv_outputs = calloc((1 << (rate * 2)), sizeof(unsigned int));
+    unsigned int output_counter = 1;
+    // for every (even-numbered) shift register state, find the concatenated output of the state
+    //   and the subsequent state that follows it (low bit set). then, check to see if this
+    //   concatenated output has a unique key assigned to it already. if not, give it a key.
+    //   if it does, retrieve the key. assign this key to the shift register state.
+    for (unsigned int i = 0; i < (1 << (order - 1)); i++) {
+        // first get the concatenated pair of outputs
+        unsigned int out = table[i * 2 + 1];
+        out <<= rate;
+        out |= table[i * 2];
+
+        // does this concatenated output exist in the outputs table yet?
+        if (!inv_outputs[out]) {
+            // doesn't exist, allocate a new key
+            inv_outputs[out] = output_counter;
+            pairs.outputs[output_counter] = out;
+            output_counter++;
+        }
+        // set the opaque key for the ith shift register state to the concatenated output entry
+        pairs.keys[i] = inv_outputs[out];
+    }
+    pairs.outputs_len = output_counter;
+    pairs.output_mask = (1 << (rate)) - 1;
+    pairs.output_width = rate;
+    pairs.distances = calloc(pairs.outputs_len, sizeof(distance_pair_t));
+    free(inv_outputs);
+    return pairs;
+}
+
+void pair_lookup_destroy(pair_lookup_t pairs) {
+    free(pairs.keys);
+    free(pairs.outputs);
+    free(pairs.distances);
+}
+
+void pair_lookup_fill_distance(pair_lookup_t pairs, distance_t *distances) {
+    for (unsigned int i = 1; i < pairs.outputs_len; i += 1) {
+        output_pair_t concat_out = pairs.outputs[i];
+        unsigned int i_0 = concat_out & pairs.output_mask;
+        concat_out >>= pairs.output_width;
+        unsigned int i_1 = concat_out;
+
+        pairs.distances[i] = (distances[i_1] << 16) | distances[i_0];
+    }
+}