thirdparty/scummvm
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COMMON: Rework the BitStream class to improve its performance

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* Fixed peekBits not to seek the underlying stream. Seeking can be slow
  when the stream is a file.
* Changed multi-bit  operations to work on multiple bits at once rather
  than iterating over single-bit operations.

This is an almost direct port of a patch for xoreos provided by DrMcCoy.
This commit is contained in:
Bastien Bouclet 2019-04-08 19:23:31 +02:00 • committed by Filippos Karapetis
parent 2af325f60a
commit ae9eeb731f
2 changed files with 149 additions and 135 deletions
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50
test/common/bitstream.h
View file

@ -50,7 +50,7 @@ public:
private:
template<class MS, class BS>
void tmpl_skip() {
byte contents[] = { 'a', 'b' };
byte contents[] = { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j' };
MS ms(contents, sizeof(contents));
@ -61,6 +61,8 @@ private:
bs.skip(4);
TS_ASSERT_EQUALS(bs.pos(), 9u);
TS_ASSERT_EQUALS(bs.getBits(3), 6u);
bs.skip(65);
TS_ASSERT_EQUALS(bs.pos(), 77u);
TS_ASSERT(!bs.eos());
}
public:
@ -133,7 +135,7 @@ private:
TS_ASSERT_EQUALS(bs.pos(), 3u);
bs.skip(8);
TS_ASSERT_EQUALS(bs.pos(), 11u);
TS_ASSERT_EQUALS(bs.peekBits(5), 2u);
TS_ASSERT_EQUALS(bs.peekBits(6), 4u);
TS_ASSERT(!bs.eos());
}
public:
@ -203,7 +205,7 @@ private:
TS_ASSERT_EQUALS(bs.pos(), 3u);
bs.skip(8);
TS_ASSERT_EQUALS(bs.pos(), 11u);
TS_ASSERT_EQUALS(bs.peekBits(5), 12u);
TS_ASSERT_EQUALS(bs.peekBits(20), 12u);
TS_ASSERT(!bs.eos());
}
public:
@ -211,4 +213,46 @@ public:
tmpl_peek_bits_lsb<Common::MemoryReadStream, Common::BitStream8LSB>();
tmpl_peek_bits_lsb<Common::BitStreamMemoryStream, Common::BitStreamMemory8LSB>();
}
private:
template<class MS, class BS>
void tmpl_align() {
byte contents[] = { 'a', 'b' };
MS ms(contents, sizeof(contents));
BS bs(ms);
TS_ASSERT_EQUALS(bs.pos(), 0u);
bs.align();
TS_ASSERT_EQUALS(bs.pos(), 0u);
bs.skip(3);
bs.align();
TS_ASSERT_EQUALS(bs.pos(), 8u);
}
public:
void test_align() {
tmpl_align<Common::MemoryReadStream, Common::BitStream8LSB>();
tmpl_align<Common::BitStreamMemoryStream, Common::BitStreamMemory8LSB>();
}
private:
template<class MS, class BS>
void tmpl_align_16() {
byte contents[] = { 'a', 'b' };
MS ms(contents, sizeof(contents));
BS bs(ms);
TS_ASSERT_EQUALS(bs.pos(), 0u);
bs.align();
TS_ASSERT_EQUALS(bs.pos(), 0u);
bs.skip(3);
bs.align();
TS_ASSERT_EQUALS(bs.pos(), 16u);
}
public:
void test_align_16() {
tmpl_align_16<Common::MemoryReadStream, Common::BitStream16BELSB>();
tmpl_align_16<Common::BitStreamMemoryStream, Common::BitStreamMemory16BELSB>();
}
};