commit faa7fcfe1c8fe70f51fa5d00f7b61236b238dde9
author Thomas Davies <thdavies@cisco.com> Mon Nov 14 11:59:43 2016 +0000
committer Yaowu Xu <yaowu@google.com> Wed Nov 16 03:57:10 2016 +0000
tree 58f5fae40989f4af0ccdb0a1e0cce3956c70d6dc
parent e0f8c5590f3def87f2061ca2927c7334d03fa674

Add overwrite functions which do not zero bytes.

In several places bits are overwritten in the bitstream. These
functions avoid zeroing bytes during writing so that this can
happen correctly when the number of bits is not 8*N.

Re-addresses the attempted fix in
133c57c331f3b1806233fbd83db1f5f022b1490a

which broke threaded encoding tests, which relied on re-using
byte buffers.

Change-Id: I682c5e3a7869eac7ad475584db8bf170d47a56c9

aom_dsp/bitwriter_buffer.c

diff --git a/aom_dsp/bitwriter_buffer.c b/aom_dsp/bitwriter_buffer.c
index 9d6a0da..c341ca3 100644
--- a/aom_dsp/bitwriter_buffer.c
+++ b/aom_dsp/bitwriter_buffer.c
@@ -24,6 +24,7 @@
   const int p = off / CHAR_BIT;
   const int q = CHAR_BIT - 1 - off % CHAR_BIT;
   if (q == CHAR_BIT - 1) {
+    // Zero next char and write bit
     wb->bit_buffer[p] = bit << q;
   } else {
     wb->bit_buffer[p] &= ~(1 << q);
@@ -32,11 +33,28 @@
   wb->bit_offset = off + 1;
 }
 
+void aom_wb_overwrite_bit(struct aom_write_bit_buffer *wb, int bit) {
+  // Do not zero bytes but overwrite exisiting values
+  const int off = (int)wb->bit_offset;
+  const int p = off / CHAR_BIT;
+  const int q = CHAR_BIT - 1 - off % CHAR_BIT;
+  wb->bit_buffer[p] &= ~(1 << q);
+  wb->bit_buffer[p] |= bit << q;
+  wb->bit_offset = off + 1;
+}
+
 void aom_wb_write_literal(struct aom_write_bit_buffer *wb, int data, int bits) {
   int bit;
   for (bit = bits - 1; bit >= 0; bit--) aom_wb_write_bit(wb, (data >> bit) & 1);
 }
 
+void aom_wb_overwrite_literal(struct aom_write_bit_buffer *wb, int data,
+                              int bits) {
+  int bit;
+  for (bit = bits - 1; bit >= 0; bit--)
+    aom_wb_overwrite_bit(wb, (data >> bit) & 1);
+}
+
 void aom_wb_write_inv_signed_literal(struct aom_write_bit_buffer *wb, int data,
                                      int bits) {
   aom_wb_write_literal(wb, data, bits + 1);

aom_dsp/bitwriter_buffer.h

diff --git a/aom_dsp/bitwriter_buffer.h b/aom_dsp/bitwriter_buffer.h
index 63027ef..8160765 100644
--- a/aom_dsp/bitwriter_buffer.h
+++ b/aom_dsp/bitwriter_buffer.h
@@ -27,8 +27,13 @@
 
 void aom_wb_write_bit(struct aom_write_bit_buffer *wb, int bit);
 
+void aom_wb_overwrite_bit(struct aom_write_bit_buffer *wb, int bit);
+
 void aom_wb_write_literal(struct aom_write_bit_buffer *wb, int data, int bits);
 
+void aom_wb_overwrite_literal(struct aom_write_bit_buffer *wb, int data,
+                              int bits);
+
 void aom_wb_write_inv_signed_literal(struct aom_write_bit_buffer *wb, int data,
                                      int bits);