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Remove ReadOneBit() and ReadSymbolUnsafe()

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Simplify and re-organize the VP8L bit-reader functions
(e.g.: the 40-bit look-ahead code was helping much)

Speed-up with LBITS=64, on arm7-a:

=> before:
./dwebp_justify_24_neon -v bryce_ll.webp
Time to decode picture: 11.393s
File bryce_ll.webp can be decoded (dimensions: 11158 x 2156).
...

=> after (LBITS=64):	Time to decode picture: 9.953s

making the VP8L bit-reader in 32 bit mode is going to be
harder (because we need to be able to read two symbols
at a time, each with max length 15 bits)

Change-Id: I89746fb103b87b5e2fd40a3208a6fbc584b88297
This commit is contained in:
skal
2013-02-20 00:13:23 +01:00
parent b7490f8553
commit 1667bded67
3 changed files with 53 additions and 93 deletions
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33
src/utils/bit_reader.h
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@@ -258,14 +258,16 @@ static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) {
// -----------------------------------------------------------------------------
// Bitreader for lossless format
typedef uint64_t vp8l_val_t; // right now, this bit-reader can only use 64bit.
typedef struct {
uint64_t val_;
const uint8_t* buf_;
size_t len_;
size_t pos_;
int bit_pos_;
int eos_;
int error_;
vp8l_val_t val_; // pre-fetched bits
const uint8_t* buf_; // input byte buffer
size_t len_; // buffer length
size_t pos_; // byte position in buf_
int bit_pos_; // current bit-reading position in val_
int eos_; // bitstream is finished
int error_; // an error occurred (buffer overflow attempt...)
} VP8LBitReader;
void VP8LInitBitReader(VP8LBitReader* const br,
@@ -281,17 +283,14 @@ void VP8LBitReaderSetBuffer(VP8LBitReader* const br,
// Flags eos if this read attempt is going to cross the read buffer.
uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits);
// Reads one bit from Read Buffer. Flags an error in case end_of_stream.
// Flags eos after reading last bit from the buffer.
uint32_t VP8LReadOneBit(VP8LBitReader* const br);
// Return the prefetched bits, so they can be looked up.
static WEBP_INLINE uint32_t VP8LPrefetchBits(VP8LBitReader* const br) {
return (uint32_t)(br->val_ >> br->bit_pos_);
}
// VP8LReadOneBitUnsafe is faster than VP8LReadOneBit, but it can be called only
// 32 times after the last VP8LFillBitWindow. Any subsequent calls
// (without VP8LFillBitWindow) will return invalid data.
static WEBP_INLINE uint32_t VP8LReadOneBitUnsafe(VP8LBitReader* const br) {
const uint32_t val = (uint32_t)((br->val_ >> br->bit_pos_) & 1);
++br->bit_pos_;
return val;
// Discard 'num_bits' bits from the cache.
static WEBP_INLINE void VP8LDiscardBits(VP8LBitReader* const br, int num_bits) {
br->bit_pos_ += num_bits;
}
// Advances the Read buffer by 4 bytes to make room for reading next 32 bits.