commit 12401f7d2dab48cc01387c58636c2e93db9c738d
author Lei Zhang <thestig@chromium.org> Tue May 15 01:36:51 2018 +0000
committer Chromium commit bot <commit-bot@chromium.org> Tue May 15 01:36:51 2018 +0000
tree 4ab0dc643504b844e4a51cbe30267433ab768273
parent ce03169f65a105f0abfbf737d162a3418ab5f637

Read data in bigger chunks in fax codec code.

In case there are long runs of data to be skipped, FindBit() runs much
faster reading and comparing 8 bytes at a time.

BUG=chromium:834633

Change-Id: Ifc7b348d123c5a72cf09fbf53d764075f8abfba0
Reviewed-on: https://pdfium-review.googlesource.com/32513
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>

core/fxcodec/codec/fx_codec_fax.cpp

diff --git a/core/fxcodec/codec/fx_codec_fax.cpp b/core/fxcodec/codec/fx_codec_fax.cpp
index 20280a3..9739101 100644
--- a/core/fxcodec/codec/fx_codec_fax.cpp
+++ b/core/fxcodec/codec/fx_codec_fax.cpp
@@ -66,9 +66,21 @@
 
     start_pos += 7;
   }
-  uint8_t skip = bit ? 0x00 : 0xff;
+  const uint8_t skip = bit ? 0x00 : 0xff;
+  const int max_byte = (max_pos + 7) / 8;
   int byte_pos = start_pos / 8;
-  int max_byte = (max_pos + 7) / 8;
+
+  // Try reading in bigger chunks in case there are long runs to be skipped.
+  static constexpr int kBulkReadSize = 8;
+  if (max_byte >= kBulkReadSize && byte_pos < max_byte - kBulkReadSize) {
+    uint8_t skip_block[kBulkReadSize];
+    memset(skip_block, skip, kBulkReadSize);
+    while (byte_pos < max_byte - kBulkReadSize &&
+           memcmp(data_buf + byte_pos, skip_block, kBulkReadSize) == 0) {
+      byte_pos += kBulkReadSize;
+    }
+  }
+
   while (byte_pos < max_byte) {
     if (data_buf[byte_pos] != skip)
       break;