Add ARC non-repeat packing decompression implementation and tests.

2025-12-16 19:24:31 +00:00 · 2025-09-01 23:30:57 +01:00
parent 750df1cca9
commit bfb9a6b524
6 changed files with 3799 additions and 3 deletions
--- a/arc/pack.c
+++ b/arc/pack.c
@@ -0,0 +1,78 @@
+/*
+ * This file is part of the Aaru Data Preservation Suite.
+ * Copyright (c) 2019-2025 Natalia Portillo.
+ * Copyright © 2018-2019 David Ryskalczyk
+ *
+ * This library is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of the
+ * License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <string.h>
+#include "../library.h"
+
+#define DLE 0x90  // Data Link Escape character, used as a repeat marker.
+
+// Decompresses data using non-repeat packing.
+// This algorithm encodes runs of identical bytes.
+int arc_decompress_pack(const unsigned char *in_buf, size_t in_len, unsigned char *out_buf, size_t *out_len)
+{
+    // Basic validation of pointers.
+    if(!in_buf || !out_buf || !out_len) { return -1; }
+
+    size_t        in_pos  = 0;
+    size_t        out_pos = 0;
+    unsigned char state   = 0;  // 0 for normal (NOHIST), 1 for in-repeat (INREP).
+    unsigned char lastc   = 0;  // Last character seen.
+
+    // Loop through the input buffer until it's exhausted or the output buffer is full.
+    while(in_pos < in_len && out_pos < *out_len)
+    {
+        if(state == 1)
+        {  // We are in a repeat sequence.
+            if(in_buf[in_pos])
+            {  // The byte after DLE is the repeat count.
+                unsigned char count = in_buf[in_pos];
+                // Write the last character 'count' times.
+                while(--count && out_pos < *out_len) { out_buf[out_pos++] = lastc; }
+            }
+            else
+            {  // A count of 0 means the DLE character itself should be written.
+                if(out_pos < *out_len) { out_buf[out_pos++] = DLE; }
+            }
+            state = 0;  // Return to normal state.
+            in_pos++;
+        }
+        else
+        {  // Normal state.
+            if(in_buf[in_pos] != DLE)
+            {  // Not a repeat sequence.
+                if(out_pos < *out_len)
+                {
+                    // Copy the character and save it as the last character.
+                    out_buf[out_pos++] = lastc = in_buf[in_pos];
+                }
+            }
+            else
+            {               // DLE marks the start of a repeat sequence.
+                state = 1;  // Enter repeat state.
+            }
+            in_pos++;
+        }
+    }
+
+    // Update the output length to the number of bytes written.
+    *out_len = out_pos;
+    // Return success.
+    return 0;
+}