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-rw-r--r--third_party/libwebp/utils/bit_reader.h231
1 files changed, 181 insertions, 50 deletions
diff --git a/third_party/libwebp/utils/bit_reader.h b/third_party/libwebp/utils/bit_reader.h
index 36fc13e..ccf450c 100644
--- a/third_party/libwebp/utils/bit_reader.h
+++ b/third_party/libwebp/utils/bit_reader.h
@@ -24,11 +24,80 @@
extern "C" {
#endif
-#define BITS 32 // can be 32, 16 or 8
-#define MASK ((((bit_t)1) << (BITS)) - 1)
-#if (BITS == 32)
-typedef uint64_t bit_t; // natural register type
-typedef uint32_t lbit_t; // natural type for memory I/O
+// The Boolean decoder needs to maintain infinite precision on the value_ field.
+// However, since range_ is only 8bit, we only need an active window of 8 bits
+// for value_. Left bits (MSB) gets zeroed and shifted away when value_ falls
+// below 128, range_ is updated, and fresh bits read from the bitstream are
+// brought in as LSB.
+// To avoid reading the fresh bits one by one (slow), we cache a few of them
+// ahead (actually, we cache BITS of them ahead. See below). There's two
+// strategies regarding how to shift these looked-ahead fresh bits into the
+// 8bit window of value_: either we shift them in, while keeping the position of
+// the window fixed. Or we slide the window to the right while keeping the cache
+// bits at a fixed, right-justified, position.
+//
+// Example, for BITS=16: here is the content of value_ for both strategies:
+//
+// !USE_RIGHT_JUSTIFY || USE_RIGHT_JUSTIFY
+// ||
+// <- 8b -><- 8b -><- BITS bits -> || <- 8b+3b -><- 8b -><- 13 bits ->
+// [unused][value_][cached bits][0] || [unused...][value_][cached bits]
+// [........00vvvvvvBBBBBBBBBBBBB000]LSB || [...........00vvvvvvBBBBBBBBBBBBB]
+// ||
+// After calling VP8Shift(), where we need to shift away two zeros:
+// [........vvvvvvvvBBBBBBBBBBB00000]LSB || [.............vvvvvvvvBBBBBBBBBBB]
+// ||
+// Just before we need to call VP8LoadNewBytes(), the situation is:
+// [........vvvvvv000000000000000000]LSB || [..........................vvvvvv]
+// ||
+// And just after calling VP8LoadNewBytes():
+// [........vvvvvvvvBBBBBBBBBBBBBBBB]LSB || [........vvvvvvvvBBBBBBBBBBBBBBBB]
+//
+// -> we're back to height active 'value_' bits (marked 'v') and BITS cached
+// bits (marked 'B')
+//
+// The right-justify strategy tends to use less shifts and is often faster.
+
+//------------------------------------------------------------------------------
+// BITS can be any multiple of 8 from 8 to 56 (inclusive).
+// Pick values that fit natural register size.
+
+#if !defined(WEBP_REFERENCE_IMPLEMENTATION)
+
+#define USE_RIGHT_JUSTIFY
+
+#if defined(__i386__) || defined(_M_IX86) // x86 32bit
+#define BITS 16
+#elif defined(__x86_64__) || defined(_M_X64) // x86 64bit
+#define BITS 56
+#elif defined(__arm__) || defined(_M_ARM) // ARM
+#define BITS 24
+#else // reasonable default
+#define BITS 24
+#endif
+
+#else // reference choices
+
+#define USE_RIGHT_JUSTIFY
+#define BITS 8
+
+#endif
+
+//------------------------------------------------------------------------------
+// Derived types and constants
+
+// bit_t = natural register type
+// lbit_t = natural type for memory I/O
+
+#if (BITS > 32)
+typedef uint64_t bit_t;
+typedef uint64_t lbit_t;
+#elif (BITS == 32)
+typedef uint64_t bit_t;
+typedef uint32_t lbit_t;
+#elif (BITS == 24)
+typedef uint32_t bit_t;
+typedef uint32_t lbit_t;
#elif (BITS == 16)
typedef uint32_t bit_t;
typedef uint16_t lbit_t;
@@ -37,8 +106,15 @@ typedef uint32_t bit_t;
typedef uint8_t lbit_t;
#endif
+#ifndef USE_RIGHT_JUSTIFY
+typedef bit_t range_t; // type for storing range_
+#define MASK ((((bit_t)1) << (BITS)) - 1)
+#else
+typedef uint32_t range_t; // range_ only uses 8bits here. No need for bit_t.
+#endif
+
//------------------------------------------------------------------------------
-// Bitreader and code-tree reader
+// Bitreader
typedef struct VP8BitReader VP8BitReader;
struct VP8BitReader {
@@ -47,9 +123,9 @@ struct VP8BitReader {
int eof_; // true if input is exhausted
// boolean decoder
- bit_t range_; // current range minus 1. In [127, 254] interval.
- bit_t value_; // current value
- int missing_; // number of missing bits in value_ (8bit)
+ range_t range_; // current range minus 1. In [127, 254] interval.
+ bit_t value_; // current value
+ int bits_; // number of valid bits left
};
// Initialize the bit reader and the boolean decoder.
@@ -67,12 +143,12 @@ int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits);
// Read a bit with proba 'prob'. Speed-critical function!
extern const uint8_t kVP8Log2Range[128];
-extern const bit_t kVP8NewRange[128];
+extern const range_t kVP8NewRange[128];
void VP8LoadFinalBytes(VP8BitReader* const br); // special case for the tail
static WEBP_INLINE void VP8LoadNewBytes(VP8BitReader* const br) {
- assert(br && br->buf_);
+ assert(br != NULL && br->buf_ != NULL);
// Read 'BITS' bits at a time if possible.
if (br->buf_ + sizeof(lbit_t) <= br->buf_end_) {
// convert memory type to register type (with some zero'ing!)
@@ -80,68 +156,124 @@ static WEBP_INLINE void VP8LoadNewBytes(VP8BitReader* const br) {
lbit_t in_bits = *(lbit_t*)br->buf_;
br->buf_ += (BITS) >> 3;
#if !defined(__BIG_ENDIAN__)
-#if (BITS == 32)
+#if (BITS > 32)
+// gcc 4.3 has builtin functions for swap32/swap64
+#if defined(__GNUC__) && \
+ (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3))
+ bits = (bit_t)__builtin_bswap64(in_bits);
+#elif defined(_MSC_VER)
+ bits = (bit_t)_byteswap_uint64(in_bits);
+#elif defined(__x86_64__)
+ __asm__ volatile("bswapq %0" : "=r"(bits) : "0"(in_bits));
+#else // generic code for swapping 64-bit values (suggested by bdb@)
+ bits = (bit_t)in_bits;
+ bits = ((bits & 0xffffffff00000000ull) >> 32) |
+ ((bits & 0x00000000ffffffffull) << 32);
+ bits = ((bits & 0xffff0000ffff0000ull) >> 16) |
+ ((bits & 0x0000ffff0000ffffull) << 16);
+ bits = ((bits & 0xff00ff00ff00ff00ull) >> 8) |
+ ((bits & 0x00ff00ff00ff00ffull) << 8);
+#endif
+ bits >>= 64 - BITS;
+#elif (BITS >= 24)
#if defined(__i386__) || defined(__x86_64__)
__asm__ volatile("bswap %k0" : "=r"(in_bits) : "0"(in_bits));
- bits = (bit_t)in_bits; // 32b -> 64b zero-extension
+ bits = (bit_t)in_bits; // 24b/32b -> 32b/64b zero-extension
#elif defined(_MSC_VER)
- bits = _byteswap_ulong(in_bits);
+ bits = (bit_t)_byteswap_ulong(in_bits);
#else
bits = (bit_t)(in_bits >> 24) | ((in_bits >> 8) & 0xff00)
| ((in_bits << 8) & 0xff0000) | (in_bits << 24);
#endif // x86
+ bits >>= (32 - BITS);
#elif (BITS == 16)
// gcc will recognize a 'rorw $8, ...' here:
bits = (bit_t)(in_bits >> 8) | ((in_bits & 0xff) << 8);
+#else // BITS == 8
+ bits = (bit_t)in_bits;
#endif
-#else // LITTLE_ENDIAN
+#else // BIG_ENDIAN
bits = (bit_t)in_bits;
#endif
- br->value_ |= bits << br->missing_;
- br->missing_ -= (BITS);
+#ifndef USE_RIGHT_JUSTIFY
+ br->value_ |= bits << (-br->bits_);
+#else
+ br->value_ = bits | (br->value_ << (BITS));
+#endif
+ br->bits_ += (BITS);
} else {
VP8LoadFinalBytes(br); // no need to be inlined
}
}
-static WEBP_INLINE int VP8BitUpdate(VP8BitReader* const br, bit_t split) {
- const bit_t value_split = split | (MASK);
- if (br->missing_ > 0) { // Make sure we have a least BITS bits in 'value_'
+static WEBP_INLINE int VP8BitUpdate(VP8BitReader* const br, range_t split) {
+ if (br->bits_ < 0) { // Make sure we have a least BITS bits in 'value_'
VP8LoadNewBytes(br);
}
- if (br->value_ > value_split) {
- br->range_ -= value_split + 1;
- br->value_ -= value_split + 1;
+#ifndef USE_RIGHT_JUSTIFY
+ split |= (MASK);
+ if (br->value_ > split) {
+ br->range_ -= split + 1;
+ br->value_ -= split + 1;
return 1;
} else {
- br->range_ = value_split;
+ br->range_ = split;
return 0;
}
+#else
+ {
+ const int pos = br->bits_;
+ const range_t value = (range_t)(br->value_ >> pos);
+ if (value > split) {
+ br->range_ -= split + 1;
+ br->value_ -= (bit_t)(split + 1) << pos;
+ return 1;
+ } else {
+ br->range_ = split;
+ return 0;
+ }
+ }
+#endif
}
static WEBP_INLINE void VP8Shift(VP8BitReader* const br) {
+#ifndef USE_RIGHT_JUSTIFY
// range_ is in [0..127] interval here.
- const int idx = br->range_ >> (BITS);
+ const bit_t idx = br->range_ >> (BITS);
const int shift = kVP8Log2Range[idx];
br->range_ = kVP8NewRange[idx];
br->value_ <<= shift;
- br->missing_ += shift;
+ br->bits_ -= shift;
+#else
+ const int shift = kVP8Log2Range[br->range_];
+ assert(br->range_ < (range_t)128);
+ br->range_ = kVP8NewRange[br->range_];
+ br->bits_ -= shift;
+#endif
}
-
static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) {
+#ifndef USE_RIGHT_JUSTIFY
// It's important to avoid generating a 64bit x 64bit multiply here.
// We just need an 8b x 8b after all.
- const bit_t split =
- (bit_t)((uint32_t)(br->range_ >> (BITS)) * prob) << ((BITS) - 8);
+ const range_t split =
+ (range_t)((uint32_t)(br->range_ >> (BITS)) * prob) << ((BITS) - 8);
+ const int bit = VP8BitUpdate(br, split);
+ if (br->range_ <= (((range_t)0x7e << (BITS)) | (MASK))) {
+ VP8Shift(br);
+ }
+ return bit;
+#else
+ const range_t split = (br->range_ * prob) >> 8;
const int bit = VP8BitUpdate(br, split);
- if (br->range_ <= (((bit_t)0x7e << (BITS)) | (MASK))) {
+ if (br->range_ <= (range_t)0x7e) {
VP8Shift(br);
}
return bit;
+#endif
}
static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) {
- const bit_t split = (br->range_ >> 1);
+ const range_t split = (br->range_ >> 1);
const int bit = VP8BitUpdate(br, split);
VP8Shift(br);
return bit ? -v : v;
@@ -149,16 +281,18 @@ static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) {
// -----------------------------------------------------------------------------
-// Bitreader
+// 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,
@@ -174,17 +308,14 @@ 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);
-
-// 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 = (br->val_ >> br->bit_pos_) & 1;
- ++br->bit_pos_;
- return val;
+// 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_);
+}
+
+// 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.
generated by cgit v1.1 at 2025-01-24 13:17:48 +0000