commit ae3fe87beb2eef73271cb6718ca575095f192b23
author Tom Sepez <tsepez@chromium.org> Wed Jul 24 18:34:45 2024 +0000
committer Pdfium LUCI CQ <pdfium-scoped@luci-project-accounts.iam.gserviceaccount.com> Wed Jul 24 18:34:45 2024 +0000
tree 36fe99a419f27f6a82d9c177d23c19aae0e67025
parent 2e8328971d5e98ae9f218fbc080eb1063875247f

Pass spans to GetAlphaWithSrc().

Ensure code is safe before continuing to optimize it for any
specific cases. Then try to get the optimizer to combine an
"arg-not-present" branch with a subsequent bounds check.

Change-Id: Ie9b92e78007a3c8c492a97c651dcc6af34ec8773
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/122415
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Tom Sepez <tsepez@google.com>

core/fxge/dib/cfx_scanlinecompositor.cpp

diff --git a/core/fxge/dib/cfx_scanlinecompositor.cpp b/core/fxge/dib/cfx_scanlinecompositor.cpp
index 1e74f92..8840383 100644
--- a/core/fxge/dib/cfx_scanlinecompositor.cpp
+++ b/core/fxge/dib/cfx_scanlinecompositor.cpp
@@ -109,17 +109,15 @@
 }
 
 int GetAlphaWithSrc(uint8_t src_alpha,
-                    const uint8_t* clip_scan,
-                    const uint8_t* src_scan,
-                    int col) {
-  UNSAFE_TODO({
-    int result = src_alpha * src_scan[col];
-    if (clip_scan) {
-      result *= clip_scan[col];
-      result /= 255;
-    }
-    return result / 255;
-  });
+                    pdfium::span<const uint8_t> clip_scan,
+                    pdfium::span<const uint8_t> src_scan,
+                    size_t col) {
+  int result = src_alpha * src_scan[col];
+  if (col < clip_scan.size()) {
+    result *= clip_scan[col];
+    result /= 255;
+  }
+  return result / 255;
 }
 
 void CompositeRow_AlphaToMask(pdfium::span<uint8_t> dest_span,
@@ -947,11 +945,9 @@
                                 BlendMode blend_type,
                                 pdfium::span<const uint8_t> clip_span) {
   uint8_t* dest_scan = dest_span.data();
-  const uint8_t* src_scan = src_span.data();
-  const uint8_t* clip_scan = clip_span.data();
   UNSAFE_TODO({
     for (int col = 0; col < pixel_count; col++) {
-      int src_alpha = GetAlphaWithSrc(mask_alpha, clip_scan, src_scan, col);
+      int src_alpha = GetAlphaWithSrc(mask_alpha, clip_span, src_span, col);
       uint8_t back_alpha = dest_scan[3];
       if (back_alpha == 0) {
         FXARGB_SetDIB(dest_scan, ArgbEncode(src_alpha, src_r, src_g, src_b));
@@ -1015,11 +1011,9 @@
                                int Bpp,
                                pdfium::span<const uint8_t> clip_span) {
   uint8_t* dest_scan = dest_span.data();
-  const uint8_t* src_scan = src_span.data();
-  const uint8_t* clip_scan = clip_span.data();
   UNSAFE_TODO({
     for (int col = 0; col < pixel_count; col++) {
-      int src_alpha = GetAlphaWithSrc(mask_alpha, clip_scan, src_scan, col);
+      int src_alpha = GetAlphaWithSrc(mask_alpha, clip_span, src_span, col);
       if (src_alpha == 0) {
         dest_scan += Bpp;
         continue;
@@ -1065,10 +1059,8 @@
                                 int pixel_count,
                                 pdfium::span<const uint8_t> clip_span) {
   uint8_t* dest_scan = dest_span.data();
-  const uint8_t* src_scan = src_span.data();
-  const uint8_t* clip_scan = clip_span.data();
   for (int col = 0; col < pixel_count; col++) {
-    int src_alpha = GetAlphaWithSrc(mask_alpha, clip_scan, src_scan, col);
+    int src_alpha = GetAlphaWithSrc(mask_alpha, clip_span, src_span, col);
     uint8_t back_alpha = *dest_scan;
     if (!back_alpha) {
       *dest_scan = src_alpha;
@@ -1086,10 +1078,8 @@
                                 int pixel_count,
                                 pdfium::span<const uint8_t> clip_span) {
   uint8_t* dest_scan = dest_span.data();
-  const uint8_t* src_scan = src_span.data();
-  const uint8_t* clip_scan = clip_span.data();
   for (int col = 0; col < pixel_count; col++) {
-    int src_alpha = GetAlphaWithSrc(mask_alpha, clip_scan, src_scan, col);
+    int src_alpha = GetAlphaWithSrc(mask_alpha, clip_span, src_span, col);
     if (src_alpha) {
       *dest_scan = FXDIB_ALPHA_MERGE(*dest_scan, src_gray, src_alpha);
     }
@@ -1959,11 +1949,9 @@
     BlendMode blend_type,
     pdfium::span<const uint8_t> clip_span) {
   uint8_t* dest_scan = dest_span.data();
-  const uint8_t* src_scan = src_span.data();
-  const uint8_t* clip_scan = clip_span.data();
   UNSAFE_TODO({
     for (int col = 0; col < pixel_count; col++) {
-      int src_alpha = GetAlphaWithSrc(mask_alpha, clip_scan, src_scan, col);
+      int src_alpha = GetAlphaWithSrc(mask_alpha, clip_span, src_span, col);
       uint8_t back_alpha = dest_scan[3];
       if (back_alpha == 0) {
         FXARGB_SetRGBOrderDIB(dest_scan,
@@ -2025,11 +2013,9 @@
     int Bpp,
     pdfium::span<const uint8_t> clip_span) {
   uint8_t* dest_scan = dest_span.data();
-  const uint8_t* src_scan = src_span.data();
-  const uint8_t* clip_scan = clip_span.data();
   UNSAFE_TODO({
     for (int col = 0; col < pixel_count; col++) {
-      int src_alpha = GetAlphaWithSrc(mask_alpha, clip_scan, src_scan, col);
+      int src_alpha = GetAlphaWithSrc(mask_alpha, clip_span, src_span, col);
       if (src_alpha == 0) {
         dest_scan += Bpp;
         continue;