From 94655a6999731f3d76ce21b7ad76568b9657e6ea Mon Sep 17 00:00:00 2001
From: "Matthias P. Braendli" <matthias.braendli@mpb.li>
Date: Fri, 19 May 2023 15:06:43 +0200
Subject: Add text message

---
 tracker-stm32/src/compression.cpp | 97 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 tracker-stm32/src/compression.cpp

(limited to 'tracker-stm32/src/compression.cpp')

diff --git a/tracker-stm32/src/compression.cpp b/tracker-stm32/src/compression.cpp
new file mode 100644
index 0000000..9b108fd
--- /dev/null
+++ b/tracker-stm32/src/compression.cpp
@@ -0,0 +1,97 @@
+#include "compression.h"
+
+using math::wide_integer::uint512_t;
+
+uint512_t decodeBase(int b, const char *str);
+
+const char* digits = " 0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-./?@";
+
+// This function is from aprs434.github.io,
+// MIT License, Copyright (c) 2022 Serge Y. Stroobandt, ON4AA
+uint32_t encodeCallsign(const char *callsign) {
+    // Encode CCCC according to aprs434.github.io/code/codec.cpp
+    const int b = 37;
+
+    uint32_t result;
+    uint32_t weight;
+    int i, j, k, ch;
+
+    result = 0, weight = 1;
+    for (i = j = strlen(callsign); i > 0; i--) {  // iterate over input string
+        ch = toupper(callsign[i-1]);
+        for (k = 0; k < strlen(digits); k++) {    // lookup char index
+            if (digits[k] == ch) {
+                break;
+            }
+        }
+        if (k == strlen(digits))                  // ignore if ch not found in digits
+            continue;
+        result = result + ((k) * weight);
+        weight = weight * b;
+    }
+
+    return result;                                // result can be pow(42,51)!
+}
+
+// This function is from ESP32 lora.tracker,
+// MIT License, Copyright (c) 2020 Peter Buchegger
+void ax25_base91enc(char *s, uint8_t n, uint32_t v) {
+    /* Creates a Base-91 representation of the value in v in the string
+     * pointed to by s, n-characters long. String length should be n+1.
+     */
+
+    for (s += n, *s = '\0'; n; n--) {
+        *(--s) = v % 91 + 33;
+        v /= 91;
+    }
+}
+
+static void strrev(char s[])
+{
+    int length = strlen(s) ;
+    int c, i, j;
+
+    for (i = 0, j = length - 1; i < j; i++, j--)
+    {
+        c = s[i];
+        s[i] = s[j];
+        s[j] = c;
+    }
+}
+
+inline void assert(bool cond) {
+    while (!cond) {}
+}
+
+static uint8_t bytes[100];
+
+uint512_t decodeBase(int b, const char* str) {    // base b, str 64 bytes max '\0' terminated
+
+    uint512_t result;
+    uint512_t weight;
+    int i, j, k, ch;
+
+    assert(b <= strlen(digits));
+    assert(b > 1);
+
+    result = 0, weight = 1;
+    for (i = j = strlen(str); i > 0; i--)         // iterate over input string
+    {
+        ch=toupper(str[i-1]);
+        for (k = 0; k < strlen(digits); k++) {    //lookup char index
+            if (digits[k] == ch) {
+                break;
+            }
+        }
+        if (k == strlen(digits))                  // ignore if ch not found in digits
+            continue;
+        result = result + ((k) * weight);
+        weight = weight * b;
+    }
+
+    return result;                                // result can be pow(42,51)!
+}
+
+uint512_t encodetttt(const char *s) {
+    return decodeBase(42, s);
+}
-- 
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