From 8c7cd722f639ef31d571f5c41588b07ad05177a2 Mon Sep 17 00:00:00 2001
From: Urvang Joshi <urvang@google.com>
Date: Tue, 22 Apr 2014 15:13:14 -0700
Subject: [PATCH] Bugfix: Incremental decode of lossy-alpha

When remapping buffer, br->eos_ was wrongly being set to true for
certain
images.

Also, refactored the end-of-stream detection as a function.

Reported in http://crbug.com/364830

Change-Id: I716ce082ef2b505fe24246b9c14912d8e97b5d84
---
 src/utils/bit_reader.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/src/utils/bit_reader.c b/src/utils/bit_reader.c
index bfa4d7d2..79f64d36 100644
--- a/src/utils/bit_reader.c
+++ b/src/utils/bit_reader.c
@@ -141,14 +141,24 @@ void VP8LInitBitReader(VP8LBitReader* const br,
   }
 }
 
+// Special version that assumes br->pos_ <= br_len_.
+static int IsEndOfStreamSpecial(const VP8LBitReader* const br) {
+  assert(br->pos_ <= br->len_);
+  return br->pos_ == br->len_ && br->bit_pos_ >= LBITS;
+}
+
+static int IsEndOfStream(const VP8LBitReader* const br) {
+  return (br->pos_ > br->len_) || IsEndOfStreamSpecial(br);
+}
+
 void VP8LBitReaderSetBuffer(VP8LBitReader* const br,
                             const uint8_t* const buf, size_t len) {
   assert(br != NULL);
   assert(buf != NULL);
   assert(len < 0xfffffff8u);   // can't happen with a RIFF chunk.
-  br->eos_ = (br->pos_ >= len);
   br->buf_ = buf;
   br->len_ = len;
+  br->eos_ = IsEndOfStream(br);
 }
 
 // If not at EOS, reload up to LBITS byte-by-byte
@@ -175,9 +185,7 @@ void VP8LFillBitWindow(VP8LBitReader* const br) {
     }
 #endif
     ShiftBytes(br);       // Slow path.
-    if (br->pos_ == br->len_ && br->bit_pos_ >= LBITS) {
-      br->eos_ = 1;
-    }
+    br->eos_ = IsEndOfStreamSpecial(br);
   }
 }
 
@@ -190,11 +198,7 @@ uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits) {
     const int new_bits = br->bit_pos_ + n_bits;
     br->bit_pos_ = new_bits;
     // If this read is going to cross the read buffer, set the eos flag.
-    if (br->pos_ == br->len_) {
-      if (new_bits >= LBITS) {
-        br->eos_ = 1;
-      }
-    }
+    br->eos_ = IsEndOfStreamSpecial(br);
     ShiftBytes(br);
     return val;
   } else {