Bug 847479 - Add smart filters borrowed from xz-utils to improve SeekableZStream compression rate. r=nfroyd

mozglue/linker/Makefile.in

@@ -35,3 +35,11 @@ CPPSRCS += \
   $(NULL)
 
 include $(topsrcdir)/config/rules.mk
+
+ifeq (arm,$(TARGET_CPU))
+ifdef MOZ_THUMB2
+HOST_CXXFLAGS += -DTARGET_THUMB
+else
+HOST_CXXFLAGS += -DTARGET_ARM
+endif
+endif

mozglue/linker/SeekableZStream.cpp

@@ -29,6 +29,7 @@ SeekableZStream::Init(const void *buf, size_t length)
   lastChunkSize = header->lastChunkSize;
   windowBits = header->windowBits;
   offsetTable.Init(&header[1], header->nChunks);
+  filter = GetFilter(header->filter);
 
   /* Sanity check */
   if ((chunkSize == 0) ||
@@ -99,5 +100,80 @@ SeekableZStream::DecompressChunk(void *where, size_t chunk, size_t length)
     log("inflateEnd failed: %s", zStream.msg);
     return false;
   }
+  if (filter)
+    filter(chunk * chunkSize, UNFILTER, (unsigned char *)where, chunkLen);
+
   return true;
 }
+
+/* Branch/Call/Jump conversion filter for Thumb, derived from xz-utils
+ * by Igor Pavlov and Lasse Collin, published in the public domain */
+static void
+BCJ_Thumb_filter(off_t offset, SeekableZStream::FilterDirection dir,
+                 unsigned char *buf, size_t size)
+{
+  size_t i;
+  for (i = 0; i + 4 <= size; i += 2) {
+    if ((buf[i + 1] & 0xf8) == 0xf0 && (buf[i + 3] & 0xf8) == 0xf8) {
+      uint32_t src = (buf[i] << 11)
+                     | ((buf[i + 1] & 0x07) << 19)
+                     | buf[i + 2]
+                     | ((buf[i + 3] & 0x07) << 8);
+      src <<= 1;
+      uint32_t dest;
+      if (dir == SeekableZStream::FILTER)
+        dest = offset + (uint32_t)(i) + 4 + src;
+      else
+        dest = src - (offset + (uint32_t)(i) + 4);
+
+      dest >>= 1;
+      buf[i] = dest >> 11;
+      buf[i + 1] = 0xf0 | ((dest >> 19) & 0x07);
+      buf[i + 2] = dest;
+      buf[i + 3] = 0xf8 | ((dest >> 8) & 0x07);
+      i += 2;
+    }
+  }
+}
+
+/* Branch/Call/Jump conversion filter for ARM, derived from xz-utils
+ * by Igor Pavlov and Lasse Collin, published in the public domain */
+static void
+BCJ_ARM_filter(off_t offset, SeekableZStream::FilterDirection dir,
+               unsigned char *buf, size_t size)
+{
+  size_t i;
+  for (i = 0; i + 4 <= size; i += 4) {
+    if (buf[i + 3] == 0xeb) {
+      uint32_t src = buf[i]
+                     | (buf[i + 1] << 8)
+                     | (buf[i + 2] << 16);
+      src <<= 2;
+      uint32_t dest;
+      if (dir == SeekableZStream::FILTER)
+        dest = offset + (uint32_t)(i) + 8 + src;
+      else
+        dest = src - (offset + (uint32_t)(i) + 8);
+
+      dest >>= 2;
+      buf[i] = dest;
+      buf[i + 1] = dest >> 8;
+      buf[i + 2] = dest >> 16;
+    }
+  }
+}
+
+
+SeekableZStream::ZStreamFilter
+SeekableZStream::GetFilter(SeekableZStream::FilterId id)
+{
+  switch (id) {
+  case BCJ_THUMB:
+    return BCJ_Thumb_filter;
+  case BCJ_ARM:
+    return BCJ_ARM_filter;
+  default:
+    return NULL;
+  }
+  return NULL;
+}

mozglue/linker/SeekableZStream.h

@@ -22,7 +22,8 @@ struct SeekableZStreamHeader: public Zip::SignedEntity<SeekableZStreamHeader>
 {
   SeekableZStreamHeader()
   : Zip::SignedEntity<SeekableZStreamHeader>(magic)
-  , totalSize(0), chunkSize(0), nChunks(0), lastChunkSize(0), windowBits(0) { }
+  , totalSize(0), chunkSize(0), nChunks(0), lastChunkSize(0), windowBits(0)
+  , filter(0) { }
 
   /* Reuse Zip::SignedEntity to handle the magic number used in the Seekable
    * ZStream file format. The magic number is "SeZz". */
@@ -43,8 +44,8 @@ struct SeekableZStreamHeader: public Zip::SignedEntity<SeekableZStreamHeader>
   /* windowBits value used when deflating */
   signed char windowBits;
 
-  /* Padding */
-  unsigned char unused;
+  /* Filter Id */
+  unsigned char filter;
 
   /* Maximum supported size for chunkSize */
   /* Can't use std::min here because it's not constexpr */
@@ -94,6 +95,28 @@ public:
     return offsetTable.numElements();
   }
 
+  /**
+   * Filters used to improve compression rate.
+   */
+  enum FilterDirection {
+    FILTER,
+    UNFILTER
+  };
+  typedef void (*ZStreamFilter)(off_t, FilterDirection,
+                                  unsigned char *, size_t);
+
+  enum FilterId {
+    NONE,
+    BCJ_THUMB,
+    BCJ_ARM,
+    FILTER_MAX
+  };
+  static ZStreamFilter GetFilter(FilterId id);
+
+  static ZStreamFilter GetFilter(uint16_t id) {
+    return GetFilter(static_cast<FilterId>(id));
+  }
+
 private:
   /* RAW Seekable SZtream buffer */
   const unsigned char *buffer;
@@ -112,6 +135,9 @@ private:
 
   /* Offsets table */
   Array<le_uint32> offsetTable;
+
+  /* Filter */
+  ZStreamFilter filter;
 };
 
 #endif /* SeekableZStream_h */

mozglue/linker/szip.cpp

@@ -80,18 +80,31 @@ public:
           const char *outName, Buffer &outBuf);
 };
 
+
 class SzipCompress: public SzipAction
 {
 public:
   int run(const char *name, Buffer &origBuf,
           const char *outName, Buffer &outBuf);
 
-  SzipCompress(size_t aChunkSize)
+  SzipCompress(size_t aChunkSize, SeekableZStream::FilterId aFilter)
   : chunkSize(aChunkSize ? aChunkSize : 16384)
+  , filter(aFilter == SeekableZStream::FILTER_MAX ? DEFAULT_FILTER : aFilter)
   {}
 
 private:
+
+  const static SeekableZStream::FilterId DEFAULT_FILTER =
+#if defined(TARGET_THUMB)
+    SeekableZStream::BCJ_THUMB;
+#elif defined(TARGET_ARM)
+    SeekableZStream::BCJ_ARM;
+#else
+    SeekableZStream::NONE;
+#endif
+
   size_t chunkSize;
+  SeekableZStream::FilterId filter;
 };
 
 /* Decompress a seekable compressed stream */
@@ -153,6 +166,7 @@ int SzipCompress::run(const char *name, Buffer &origBuf,
   header->chunkSize = chunkSize;
   header->totalSize = offset;
   header->windowBits = -15; // Raw stream, window size of 32k.
+  header->filter = filter;
 
   /* Initialize zlib structure */
   z_stream zStream;
@@ -160,7 +174,29 @@ int SzipCompress::run(const char *name, Buffer &origBuf,
   zStream.avail_out = origSize - offset;
   zStream.next_out = static_cast<Bytef*>(outBuf) + offset;
 
-  Bytef *origData = static_cast<Bytef*>(origBuf);
+  /* Filter buffer */
+  SeekableZStream::ZStreamFilter filter =
+    SeekableZStream::GetFilter(header->filter);
+  Buffer filteredData;
+  Bytef *origData;
+  if (filter) {
+    filteredData.Resize(origSize);
+    origData = filteredData;
+    memcpy(origData, origBuf, origSize);
+    size_t size = origSize;
+    Bytef *data = origData;
+    size_t avail = 0;
+    /* Filter needs to be applied in chunks. */
+    while (size) {
+      avail = std::min(size, chunkSize);
+      filter(data - origData, SeekableZStream::FILTER, data, avail);
+      size -= avail;
+      data += avail;
+    }
+  } else {
+    origData = origBuf;
+  }
+
   size_t avail = 0;
   size_t size = origSize;
   while (size) {
@@ -233,6 +269,7 @@ int main(int argc, char* argv[])
   char **firstArg;
   bool compress = true;
   size_t chunkSize = 0;
+  SeekableZStream::FilterId filter = SeekableZStream::FILTER_MAX;
 
   for (firstArg = &argv[1]; argc > 3; argc--, firstArg++) {
     if (!firstArg[0] || firstArg[0][0] != '-')
@@ -250,17 +287,30 @@ int main(int argc, char* argv[])
         log("Invalid chunk size");
         return 1;
       }
+    } else if (strcmp(firstArg[0], "-f") == 0) {
+      firstArg++;
+      argc--;
+      if (!firstArg[0])
+        break;
+      if (strcmp(firstArg[0], "arm") == 0)
+        filter = SeekableZStream::BCJ_ARM;
+      else if (strcmp(firstArg[0], "thumb") == 0)
+        filter = SeekableZStream::BCJ_THUMB;
+      else {
+        log("Invalid filter");
+        return 1;
+      }
     }
   }
 
   if (argc != 3 || !firstArg[0] || !firstArg[1] ||
       (strcmp(firstArg[0], firstArg[1]) == 0)) {
-    log("usage: %s [-d] [-c CHUNKSIZE] in_file out_file", argv[0]);
+    log("usage: %s [-d] [-c CHUNKSIZE] [-f FILTER] in_file out_file", argv[0]);
     return 1;
   }
 
   if (compress) {
-    action = new SzipCompress(chunkSize);
+    action = new SzipCompress(chunkSize, filter);
   } else {
     if (chunkSize) {
       log("-c is incompatible with -d");