Finishing up freq meas

1 files changed, 267 insertions, 0 deletions

diff --git a/controller/fw/src/ldpc_decoder.c b/controller/fw/src/ldpc_decoder.c
new file mode 100644
index 0000000..fe59d77
--- /dev/null
+++ b/controller/fw/src/ldpc_decoder.c
@@ -0,0 +1,267 @@
+
+#include <stdint.h>
+#include <unistd.h>
+#include <stdbool.h>
+#include <math.h>
+#include <stdio.h>
+
+
+void gausselimination(size_t n, size_t k, int8_t *A, int8_t *b);
+
+void inner_logbp(
+        size_t m, size_t n,
+        size_t bits_count, size_t nodes_count, const uint32_t bits_values[], const uint32_t nodes_values[],
+        int8_t Lc[],
+        float Lq[], float Lr[],
+        unsigned int n_iter,
+        float L_posteriori_out[]);
+
+//decode(384, 6, 8, ...)
+int decode(size_t n, size_t nodes_count, size_t bits_count, uint32_t bits[], int8_t y[], int8_t out[], unsigned int maxiter) {
+    const size_t m = n * nodes_count / bits_count;
+    float Lq[m*n];
+    float Lr[m*n];
+    float L_posteriori[n];
+
+    /* Calculate column bit positions from row bit positions */
+    int32_t bits_transposed[nodes_count * n];
+    for (size_t i=0; i<nodes_count * n; i++)
+        bits_transposed[i] = -1;
+
+    for (size_t i=0; i<m; i++) {
+        for (size_t j=0; j<bits_count; j++) {
+            int32_t *base = bits_transposed + bits[i*bits_count + j] * nodes_count;
+            for (; *base != -1; base++)
+                ;
+            *base = i;
+        }
+    }
+
+    /*
+    printf("Row positions: [");
+    for (size_t i=0; i<m*bits_count; i++) {
+        if (i)
+            printf(", ");
+        if (i%32 == 0)
+            printf("\n    ");
+        printf("%4d", bits[i]);
+    }
+    printf("\n]\n");
+
+    printf("Column positions: [");
+    for (size_t i=0; i<n*nodes_count; i++) {
+        if (i)
+            printf(", ");
+        if (i%32 == 0)
+            printf("\n    ");
+        printf("%4d", bits_transposed[i]);
+    }
+    printf("\n]\n");
+    */
+
+    /* Run iterative optimization algorithm */
+    for (unsigned int n_iter=0; n_iter<maxiter; n_iter++) {
+        inner_logbp(m, n, bits_count, nodes_count, bits, (uint32_t*)bits_transposed, y, Lq, Lr, n_iter, L_posteriori);
+
+        /*
+        float *arrs[3] = {Lq, Lr, L_posteriori};
+        const char *names[3] = {"Lq", "Lr", "L_posteriori"};
+        size_t lens[3] = {m*n, m*n, n};
+        const size_t head_tail = 10;
+        for (int j=0; j<3; j++) {
+            printf("%s=[", names[j]);
+            bool ellipsis = false;
+            const int w = 16;
+            for (size_t i=0; i<lens[j]; i++) {
+                if (lens[j] > 1000 && i/w > head_tail && i/w < m*n/w-head_tail) {
+                    if (!ellipsis) {
+                        ellipsis = true;
+                        printf("\n    ...");
+                    }
+                    continue;
+                }
+                if (i)
+                    printf(", ");
+                if (i%w == 0)
+                    printf("\n    ");
+                float outf = arrs[j][i];
+                char *s = outf < 0 ? "\033[91m" : (outf > 0 ? "\033[92m" : "\033[94m");
+                printf("%s% 012.6g\033[38;5;240m", s, outf);
+            }
+            printf("\n]\n");
+        }
+        */
+
+        for (size_t i=0; i<n; i++)
+            out[i] = L_posteriori[i] <= 0.0f;
+
+        for (size_t i=0; i<m; i++) {
+            bool sum = 0;
+            for (size_t j=0; j<bits_count; j++)
+                sum ^= out[bits[i*bits_count + j]];
+            if (sum)
+                continue;
+        }
+
+        fflush(stdout);
+        return n_iter;
+    }
+
+    fflush(stdout);
+    return -1;
+}
+
+/* Perform inner ext LogBP solver */
+void inner_logbp(
+        size_t m, size_t n,
+        size_t bits_count, size_t nodes_count, uint32_t const bits_values[], const uint32_t nodes_values[],
+        int8_t Lc[],
+        float Lq[], float Lr[],
+        unsigned int n_iter,
+        float L_posteriori_out[]) {
+
+    /*
+    printf("Input data: [");
+    for (size_t i=0; i<n; i++) {
+        if (i)
+            printf(", ");
+        if (i%32 == 0)
+            printf("\n    ");
+        printf("%4d", Lc[i]);
+    }
+    printf("\n]\n");
+    */
+
+    /* step 1 : Horizontal */
+    unsigned int bits_counter = 0;
+    for (size_t i=0; i<m; i++) {
+        //printf("=== i=%zu\n", i);
+        for (size_t p=bits_counter; p<bits_counter+bits_count; p++) {
+            size_t j = bits_values[p];
+            //printf("\033[38;5;240mj=%04zd ", j);
+
+            float x = 1;
+            if (n_iter == 0) {
+                for (size_t q=bits_counter; q<bits_counter+bits_count; q++) {
+                    if (bits_values[q] != j) {
+                        //int lcv = Lc[bits_values[q]];
+                        //char *s = lcv < 0 ? "\033[91m" : (lcv > 0 ? "\033[92m" : "\033[94m");
+                        //printf("nij=%04u Lc=%s%3d\033[38;5;240m ", bits_values[q], s, lcv);
+                        x *= tanhf(0.5f * Lc[bits_values[q]]);
+                    }
+                }
+
+            } else {
+                for (size_t q=bits_counter; q<bits_counter+bits_count; q++) {
+                    if (bits_values[q] != j)
+                        x *= tanhf(0.5f * Lq[i*n + bits_values[q]]);
+                }
+            }
+
+            //printf("\n==== i=%03zd p=%01zd x=%08f\n", i, p-bits_counter, x);
+
+            float num = 1 + x;
+            float denom = 1 - x;
+            if (num == 0)
+                Lr[i*n + j] = -1.0f;
+            else if (denom == 0)
+                Lr[i*n + j] = 1.0f;
+            else
+                Lr[i*n + j] = logf(num/denom);
+        }
+
+        bits_counter += bits_count;
+    }
+
+    /* step 2 : Vertical */
+    unsigned int nodes_counter = 0;
+    for (size_t j=0; j<n; j++) {
+        for (size_t p=bits_counter; p<nodes_counter+nodes_count; p++) {
+            size_t i = nodes_values[p];
+
+            Lq[i*n + j] = Lc[j];
+
+            for (size_t q=bits_counter; q<nodes_counter+nodes_count; q++) {
+                if (nodes_values[q] != i)
+                    Lq[i*n + j] += Lr[nodes_values[q]*n + j];
+            }
+        }
+
+        nodes_counter += nodes_count;
+    }
+
+    /* LLR a posteriori */
+    nodes_counter = 0;
+    for (size_t j=0; j<n; j++) {
+        float sum = 0;
+        for (size_t k=bits_counter; k<nodes_counter+nodes_count; k++)
+            sum += Lr[nodes_values[k]*n + j];
+        nodes_counter += nodes_count;
+
+        L_posteriori_out[j] = Lc[j] + sum;
+    }
+}
+
+/* Compute the original (k) bit message from a (n) bit codeword x.
+ *
+ * tG: (n, k)-matrix
+ * x: (n)-vector
+ * out: (k)-vector
+ */
+void get_message(size_t n, size_t k, int8_t *tG, int8_t *x, int8_t *out) {
+
+    gausselimination(n, k, tG, x);
+
+    out[k - 1] = x[k - 1];
+    for (ssize_t i=k-2; i>=0; i--) {
+        out[i] = x[i];
+
+        uint8_t sum = 0;
+        for (size_t j=i+1; j<k; j++)
+            sum ^= tG[i*k + j] * out[j];
+
+        out[i] = !!(out[i] - sum);
+    }
+}
+
+/* Solve linear system in Z/2Z via Gauss Gauss elimination.
+ *
+ * A: (n, k)-matrix
+ * b: (n)-vector
+ */
+void gausselimination(size_t n, size_t k, int8_t *A, int8_t *b) {
+    ssize_t d = k<n ? k : n;
+    for (ssize_t j=0; j<d; j++) {
+
+        ssize_t pivot = -1;
+        for (size_t i=j; i<n; i++) {
+            if (A[i*k + j]) {
+                pivot = i;
+                break;
+            }
+        }
+        if (pivot == -1)
+            continue;
+
+        if (pivot != j) {
+            for (size_t i=0; i<k; i++) {
+                int8_t tmp = A[j*k + i];
+                A[j*k + i] = A[pivot*k + i];
+                A[pivot*k + i] = tmp;
+            }
+
+            int8_t tmp = b[j];
+            b[j] = b[pivot];
+            b[pivot] = tmp;
+        }
+
+        for (size_t i=j+1; i<n; i++) {
+            if (A[i*k + j]) {
+                for (size_t p=0; p<k; p++)
+                    A[i*k + p] = !!(A[i*k + p] - A[j*k + p]);
+                b[i] = !!(b[i] - b[j]);
+            }
+        }
+    }
+}
+