commit ddc904a4cd3f0d88d9c43bda2d35af9eeb4069db
author Lei Zhang <thestig@chromium.org> Tue Jun 29 22:03:47 2021 +0000
committer Pdfium LUCI CQ <pdfium-scoped@luci-project-accounts.iam.gserviceaccount.com> Tue Jun 29 22:03:47 2021 +0000
tree 947458e2c042a4b25b007fd77458854e469f951b
parent cfa396005bc216026aefb9f8a6ee03d502b9b990

Remove conditionals in inner loops in CJPX_Decoder::Decode().

Check `adjust` once and choose among 3 for-loops. This results in
another 3% speedup, as measured by running:
testing/tools/safetynet_measure.py --profiler perfstat bug_1698.pdf,
where bug_1698.pdf is the PDF attached to https://crbug.com/pdfium/1698.

Change-Id: I92e46909f346486eb3d941f48ffb8ed679f4ff18
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/82773
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

core/fxcodec/jpx/cjpx_decoder.cpp

diff --git a/core/fxcodec/jpx/cjpx_decoder.cpp b/core/fxcodec/jpx/cjpx_decoder.cpp
index 270dabd..c66985a 100644
--- a/core/fxcodec/jpx/cjpx_decoder.cpp
+++ b/core/fxcodec/jpx/cjpx_decoder.cpp
@@ -539,6 +539,8 @@
     if (!comps.data)
       continue;
 
+    // Perfomance-sensitive code below. Combining these 3 for-loops below will
+    // cause a slowdown.
     const uint32_t src_offset = comps.sgnd ? 1 << (comps.prec - 1) : 0;
     if (adjust < 0) {
       for (uint32_t row = 0; row < height; ++row) {
@@ -549,19 +551,24 @@
           *pPixel = static_cast<uint8_t>(src << -adjust);
         }
       }
+    } else if (adjust == 0) {
+      for (uint32_t row = 0; row < height; ++row) {
+        uint8_t* pScanline = pChannel + row * pitch;
+        for (uint32_t col = 0; col < width; ++col) {
+          uint8_t* pPixel = pScanline + col * m_Image->numcomps;
+          int src = comps.data[row * width + col] + src_offset;
+          *pPixel = static_cast<uint8_t>(src);
+        }
+      }
     } else {
       for (uint32_t row = 0; row < height; ++row) {
         uint8_t* pScanline = pChannel + row * pitch;
         for (uint32_t col = 0; col < width; ++col) {
           uint8_t* pPixel = pScanline + col * m_Image->numcomps;
           int src = comps.data[row * width + col] + src_offset;
-          if (adjust == 0) {
-            *pPixel = static_cast<uint8_t>(src);
-          } else {
-            int pixel = (src >> adjust) + ((src >> (adjust - 1)) % 2);
-            pixel = pdfium::clamp(pixel, 0, 255);
-            *pPixel = static_cast<uint8_t>(pixel);
-          }
+          int pixel = (src >> adjust) + ((src >> (adjust - 1)) % 2);
+          pixel = pdfium::clamp(pixel, 0, 255);
+          *pPixel = static_cast<uint8_t>(pixel);
         }
       }
     }