1 files changed, 39 insertions, 0 deletions
diff --git a/third_party/aom/test/boolcoder_test.cc b/third_party/aom/test/boolcoder_test.cc
index 72182de109..680ec18774 100644
--- a/third_party/aom/test/boolcoder_test.cc
+++ b/third_party/aom/test/boolcoder_test.cc
@@ -108,6 +108,7 @@ TEST(AV1, TestTell) {
     double frac_diff_total = 0;
     GTEST_ASSERT_GE(aom_reader_tell(&br), 0u);
     GTEST_ASSERT_LE(aom_reader_tell(&br), 1u);
+    ASSERT_FALSE(aom_reader_has_overflowed(&br));
     for (int i = 0; i < kSymbols; i++) {
       aom_read(&br, p, NULL);
       uint32_t tell = aom_reader_tell(&br);
@@ -130,5 +131,43 @@ TEST(AV1, TestTell) {
     // The average frac_diff error should be pretty small.
     GTEST_ASSERT_LE(frac_diff_total / kSymbols, FRAC_DIFF_TOTAL_ERROR)
         << " frac_diff_total: " << frac_diff_total;
+    ASSERT_FALSE(aom_reader_has_overflowed(&br));
+  }
+}
+
+TEST(AV1, TestHasOverflowed) {
+  const int kBufferSize = 10000;
+  aom_writer bw;
+  uint8_t bw_buffer[kBufferSize];
+  const int kSymbols = 1024;
+  // Coders are noisier at low probabilities, so we start at p = 4.
+  for (int p = 4; p < 256; p++) {
+    aom_start_encode(&bw, bw_buffer);
+    for (int i = 0; i < kSymbols; i++) {
+      aom_write(&bw, 1, p);
+    }
+    aom_stop_encode(&bw);
+    aom_reader br;
+    aom_reader_init(&br, bw_buffer, bw.pos);
+    ASSERT_FALSE(aom_reader_has_overflowed(&br));
+    for (int i = 0; i < kSymbols; i++) {
+      GTEST_ASSERT_EQ(aom_read(&br, p, NULL), 1);
+      ASSERT_FALSE(aom_reader_has_overflowed(&br));
+    }
+    // In the worst case, the encoder uses just a tiny fraction of the last
+    // byte in the buffer. So to guarantee that aom_reader_has_overflowed()
+    // returns true, we have to consume very nearly 8 additional bits of data.
+    // In the worse case, one of the bits in that byte will be 1, and the rest
+    // will be zero. Once we are past that 1 bit, when the probability of
+    // reading zero symbol from aom_read() is high, each additional symbol read
+    // will consume very little additional data (in the case that p == 255,
+    // approximately -log_2(255/256) ~= 0.0056 bits). In that case it would
+    // take around 178 calls to consume more than 8 bits. That is only an upper
+    // bound. In practice we are not guaranteed to hit the worse case and can
+    // get away with 174 calls.
+    for (int i = 0; i < 174; i++) {
+      aom_read(&br, p, NULL);
+    }
+    ASSERT_TRUE(aom_reader_has_overflowed(&br));
   }
 }