Fix "zero-distance-code", take 2 (#506)

2 files changed, 4 insertions, 2 deletions

diff --git a/dec/decode.c b/dec/decode.c
index 1e903c8..2c2006b 100644
--- a/dec/decode.c
+++ b/dec/decode.c
@@ -1446,6 +1446,7 @@ static BROTLI_INLINE BROTLI_BOOL ReadDistanceInternal(
   }
   /* Convert the distance code to the actual distance by possibly */
   /* looking up past distances from the s->ringbuffer. */
+  s->distance_context = 0;
   if ((s->distance_code & ~0xf) == 0) {
     TakeDistanceFromRingBuffer(s);
     --s->block_length[2];
@@ -1706,6 +1707,7 @@ CommandPostDecodeLiterals:
     s->state = BROTLI_STATE_COMMAND_POST_DECODE_LITERALS;
   }
   if (s->distance_code >= 0) {
+    s->distance_context = s->distance_code ? 0 : 1;
     --s->dist_rb_idx;
     s->distance_code = s->dist_rb[s->dist_rb_idx & 3];
     goto postReadDistance;  /* We already have the implicit distance */
@@ -1714,8 +1716,6 @@ CommandPostDecodeLiterals:
   if (BROTLI_PREDICT_FALSE(s->block_length[2] == 0)) {
     BROTLI_SAFE(DecodeDistanceBlockSwitch(s));
   }
-  /* Reuse distance_context variable. */
-  s->distance_context = 0;
   BROTLI_SAFE(ReadDistance(s, br));
 postReadDistance:
   BROTLI_LOG(("[ProcessCommandsInternal] pos = %d distance = %d\n",
diff --git a/dec/state.h b/dec/state.h
index de1056d..6a8f093 100644
--- a/dec/state.h
+++ b/dec/state.h
@@ -140,6 +140,8 @@ struct BrotliDecoderStateStruct {
   /* This is true if the literal context map histogram type always matches the
   block type. It is then not needed to keep the context (faster decoding). */
   int trivial_literal_context;
+  /* Distance context is actual after command is decoded and before distance
+  is computed. After distance computation it is used as a temporary variable. */
   int distance_context;
   int meta_block_remaining_len;
   uint32_t block_length_index;