Update (#749)

Update:

 * Bazel: fix MSVC configuration
 * C: common: extended documentation and helpers around distance codes
 * C: common: enable BROTLI_DCHECK in "debug" builds
 * C: common: fix implicit trailing zero in `kPrefixSuffix`
 * C: dec: fix possible bit reader discharge for "large-window" mode
 * C: dec: simplify distance decoding via lookup table
 * C: dec: reuse decoder state members memory via union with lookup table
 * C: dec: add decoder state diagram
 * C: enc: clarify access to static dictionary
 * C: enc: improve static dictionary hash
 * C: enc: add "stream offset" parameter for parallel encoding
 * C: enc: reorganize hasher; now Q2-Q3 require exactly 256KiB
           to avoid global TCMalloc lock
 * C: enc: fix rare access to uninitialized data in ring-buffer
 * C: enc: reorganize logging / checks in `write_bits.h`
 * Java: dec: add "large-window" support
 * Java: dec: improve speed
 * Java: dec: debug and 32-bit mode are now activated via system properties
 * Java: dec: demystify some state variables (use better names)
 * Dictionary generator: add single input mode
 * Java: dec: modernize tests
 * Bazel: js: pick working commit for closure rules

1 files changed, 12 insertions, 16 deletions

diff --git a/c/enc/metablock.c b/c/enc/metablock.c
index 4e80044..b3e6c38 100644
--- a/c/enc/metablock.c
+++ b/c/enc/metablock.c
@@ -28,34 +28,30 @@ extern "C" {
 void BrotliInitDistanceParams(BrotliEncoderParams* params,
     uint32_t npostfix, uint32_t ndirect) {
   BrotliDistanceParams* dist_params = &params->dist;
-  uint32_t alphabet_size, max_distance;
+  uint32_t alphabet_size_max;
+  uint32_t alphabet_size_limit;
+  uint32_t max_distance;
 
   dist_params->distance_postfix_bits = npostfix;
   dist_params->num_direct_distance_codes = ndirect;
 
-  alphabet_size = BROTLI_DISTANCE_ALPHABET_SIZE(
+  alphabet_size_max = BROTLI_DISTANCE_ALPHABET_SIZE(
       npostfix, ndirect, BROTLI_MAX_DISTANCE_BITS);
+  alphabet_size_limit = alphabet_size_max;
   max_distance = ndirect + (1U << (BROTLI_MAX_DISTANCE_BITS + npostfix + 2)) -
       (1U << (npostfix + 2));
 
   if (params->large_window) {
-    static const uint32_t bound[BROTLI_MAX_NPOSTFIX + 1] = {0, 4, 12, 28};
-    uint32_t postfix = 1U << npostfix;
-    alphabet_size = BROTLI_DISTANCE_ALPHABET_SIZE(
+    BrotliDistanceCodeLimit limit = BrotliCalculateDistanceCodeLimit(
+        BROTLI_MAX_ALLOWED_DISTANCE, npostfix, ndirect);
+    alphabet_size_max = BROTLI_DISTANCE_ALPHABET_SIZE(
         npostfix, ndirect, BROTLI_LARGE_MAX_DISTANCE_BITS);
-    /* The maximum distance is set so that no distance symbol used can encode
-       a distance larger than BROTLI_MAX_ALLOWED_DISTANCE with all
-       its extra bits set. */
-    if (ndirect < bound[npostfix]) {
-      max_distance = BROTLI_MAX_ALLOWED_DISTANCE - (bound[npostfix] - ndirect);
-    } else if (ndirect >= bound[npostfix] + postfix) {
-      max_distance = (3U << 29) - 4 + (ndirect - bound[npostfix]);
-    } else {
-      max_distance = BROTLI_MAX_ALLOWED_DISTANCE;
-    }
+    alphabet_size_limit = limit.max_alphabet_size;
+    max_distance = limit.max_distance;
   }
 
-  dist_params->alphabet_size = alphabet_size;
+  dist_params->alphabet_size_max = alphabet_size_max;
+  dist_params->alphabet_size_limit = alphabet_size_limit;
   dist_params->max_distance = max_distance;
 }