From 2309fd5c1db2277b5647ebacc936a19889cf02bf Mon Sep 17 00:00:00 2001
From: Pascal Massimino <pascal.massimino@gmail.com>
Date: Sat, 30 Apr 2016 00:16:59 -0700
Subject: [PATCH] replace num_parts_ by num_parts_minus_one_ (unsigned)

This avoids spurious warnings and extra calculations.

Change-Id: Ibbe1b893cf89ee6b31a04d7bcbf92b4b357c8628
---
 src/dec/idec.c | 12 ++++++------
 src/dec/vp8.c  |  8 ++++----
 src/dec/vp8i.h |  4 ++--
 3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/src/dec/idec.c b/src/dec/idec.c
index 72705a18..8de13191 100644
--- a/src/dec/idec.c
+++ b/src/dec/idec.c
@@ -120,9 +120,9 @@ static void DoRemap(WebPIDecoder* const idec, ptrdiff_t offset) {
   if (idec->dec_ != NULL) {
     if (!idec->is_lossless_) {
       VP8Decoder* const dec = (VP8Decoder*)idec->dec_;
-      const int last_part = dec->num_parts_ - 1;
+      const uint32_t last_part = dec->num_parts_minus_one_;
       if (offset != 0) {
-        int p;
+        uint32_t p;
         for (p = 0; p <= last_part; ++p) {
           VP8RemapBitReader(dec->parts_ + p, offset);
         }
@@ -134,7 +134,6 @@ static void DoRemap(WebPIDecoder* const idec, ptrdiff_t offset) {
       }
       {
         const uint8_t* const last_start = dec->parts_[last_part].buf_;
-        assert(last_part >= 0);
         VP8BitReaderSetBuffer(&dec->parts_[last_part], last_start,
                               mem->buf_ + mem->end_ - last_start);
       }
@@ -465,19 +464,20 @@ static VP8StatusCode DecodeRemaining(WebPIDecoder* const idec) {
     }
     for (; dec->mb_x_ < dec->mb_w_; ++dec->mb_x_) {
       VP8BitReader* const token_br =
-          &dec->parts_[dec->mb_y_ & (dec->num_parts_ - 1)];
+          &dec->parts_[dec->mb_y_ & dec->num_parts_minus_one_];
       MBContext context;
       SaveContext(dec, token_br, &context);
       if (!VP8DecodeMB(dec, token_br)) {
         // We shouldn't fail when MAX_MB data was available
-        if (dec->num_parts_ == 1 && MemDataSize(&idec->mem_) > MAX_MB_SIZE) {
+        if (dec->num_parts_minus_one_ == 0 &&
+            MemDataSize(&idec->mem_) > MAX_MB_SIZE) {
           return IDecError(idec, VP8_STATUS_BITSTREAM_ERROR);
         }
         RestoreContext(&context, dec, token_br);
         return VP8_STATUS_SUSPENDED;
       }
       // Release buffer only if there is only one partition
-      if (dec->num_parts_ == 1) {
+      if (dec->num_parts_minus_one_ == 0) {
         idec->mem_.start_ = token_br->buf_ - idec->mem_.buf_;
         assert(idec->mem_.start_ <= idec->mem_.end_);
       }
diff --git a/src/dec/vp8.c b/src/dec/vp8.c
index 955c784d..336680c3 100644
--- a/src/dec/vp8.c
+++ b/src/dec/vp8.c
@@ -50,7 +50,7 @@ VP8Decoder* VP8New(void) {
     SetOk(dec);
     WebPGetWorkerInterface()->Init(&dec->worker_);
     dec->ready_ = 0;
-    dec->num_parts_ = 1;
+    dec->num_parts_minus_one_ = 0;
   }
   return dec;
 }
@@ -194,8 +194,8 @@ static VP8StatusCode ParsePartitions(VP8Decoder* const dec,
   size_t last_part;
   size_t p;
 
-  dec->num_parts_ = 1 << VP8GetValue(br, 2);
-  last_part = dec->num_parts_ - 1;
+  dec->num_parts_minus_one_ = (1 << VP8GetValue(br, 2)) - 1;
+  last_part = dec->num_parts_minus_one_;
   if (size < 3 * last_part) {
     // we can't even read the sizes with sz[]! That's a failure.
     return VP8_STATUS_NOT_ENOUGH_DATA;
@@ -586,7 +586,7 @@ static int ParseFrame(VP8Decoder* const dec, VP8Io* io) {
   for (dec->mb_y_ = 0; dec->mb_y_ < dec->br_mb_y_; ++dec->mb_y_) {
     // Parse bitstream for this row.
     VP8BitReader* const token_br =
-        &dec->parts_[dec->mb_y_ & (dec->num_parts_ - 1)];
+        &dec->parts_[dec->mb_y_ & dec->num_parts_minus_one_];
     if (!VP8ParseIntraModeRow(&dec->br_, dec)) {
       return VP8SetError(dec, VP8_STATUS_NOT_ENOUGH_DATA,
                          "Premature end-of-partition0 encountered.");
diff --git a/src/dec/vp8i.h b/src/dec/vp8i.h
index fed2b279..00da02ba 100644
--- a/src/dec/vp8i.h
+++ b/src/dec/vp8i.h
@@ -209,8 +209,8 @@ struct VP8Decoder {
   int tl_mb_x_, tl_mb_y_;  // top-left MB that must be in-loop filtered
   int br_mb_x_, br_mb_y_;  // last bottom-right MB that must be decoded
 
-  // number of partitions.
-  int num_parts_;
+  // number of partitions minus one.
+  uint32_t num_parts_minus_one_;
   // per-partition boolean decoders.
   VP8BitReader parts_[MAX_NUM_PARTITIONS];