1 files changed, 56 insertions, 0 deletions
diff --git a/lisiblepng/src/deflate.c b/lisiblepng/src/deflate.c
new file mode 100644
index 0000000..3f8ce2e
--- /dev/null
+++ b/lisiblepng/src/deflate.c
@@ -0,0 +1,56 @@
+#include "deflate.h"
+#include "assert.h"
+#include "bitstream.h"
+
+#define CM_LENGTH_BITS 4
+#define CINFO_LENGTH_BITS 4
+#define FCHECK_LENGTH_BITS 5
+#define FDICT_LENGTH_BITS 1
+#define FLEVEL_LENGTH_BITS 2
+
+bool deflate_decompress(Bitstream *bitstream);
+
+bool zlib_decompress(const uint8_t *compressed_data_buffer,
+                     const size_t compressed_data_length) {
+  ASSERT(compressed_data_buffer != NULL);
+
+  Bitstream bitstream;
+  Bitstream_init(&bitstream, compressed_data_buffer, compressed_data_length);
+
+  uint16_t cm = Bitstream_next_bits(&bitstream, CM_LENGTH_BITS);
+  uint16_t cinfo = Bitstream_next_bits(&bitstream, CINFO_LENGTH_BITS);
+  uint16_t fcheck = Bitstream_next_bits(&bitstream, FCHECK_LENGTH_BITS);
+  uint16_t fdict = Bitstream_next_bits(&bitstream, FDICT_LENGTH_BITS);
+  uint16_t flevel = Bitstream_next_bits(&bitstream, FLEVEL_LENGTH_BITS);
+
+  LOGN("zlib informations:\n"
+       "- CM (compression method): %d\n"
+       "- CINFO (compression info): %d\n"
+       "- FCHECK (check bits for CMF and FLG): %d\n"
+       "- FDICT (preset dictionary): %d\n"
+       "- FLEVEL (compression level): %d",
+       cm, cinfo, fcheck, fdict, flevel);
+  uint16_t cmf = bitstream.data[0];
+  uint16_t flg = bitstream.data[1];
+  if ((cmf * 256 + flg) % 31 != 0) {
+    LOG0("fcheck validation failed");
+    return false;
+  }
+
+  uint32_t dictionary_identifier = 0;
+  if (fdict != 0) {
+    uint16_t dictionary_identifier_0 = Bitstream_next_bits(&bitstream, 16);
+    uint16_t dictionary_identifier_1 = Bitstream_next_bits(&bitstream, 16);
+    dictionary_identifier =
+        (dictionary_identifier_0 << 0) + (dictionary_identifier_1 << 16);
+    LOGN("Dictionary identifier: %d", dictionary_identifier);
+  }
+
+  if (!deflate_decompress(&bitstream)) {
+    return false;
+  }
+
+  // TODO adler32 checksum
+
+  return true;
+}