implement RLE decode

src/abr.h

@@ -85,6 +85,38 @@ public:
         skip(bytes);
         return ret;
     }
+    std::vector<uint8_t> rrle(size_t encoded_bytes)
+    {
+        std::vector<uint8_t> data;
+        int32_t n;
+        for (int j = 0; j < encoded_bytes;)
+        {
+            n = ri8();
+            j++;
+            // force sign
+            if (n >= 128)
+                n -= 256; // can this even happen?
+            // copy the following char -n + 1 times
+            if (n < 0)
+            {
+                // NOP
+                if (n == -128)
+                    continue;
+                n = -n + 1;
+
+                j++;
+                for (int c = 0; c < n; c++)
+                    data.push_back(ru8());
+            }
+            else
+            {
+                // read the following n + 1 chars (no compr)
+                for (int c = 0; c < n + 1; c++, j++)
+                    data.push_back(ru8());
+            }
+        }
+        return data;
+    }
 protected:
     template<typename T> inline T align4(T x) { return ((x - T{1}) & (~(T{3}))) + T{4}; }
     template<typename T> T read()