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// Copyright (c) the JPEG XL Project Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
#ifndef LIB_JPEGLI_BIT_WRITER_H_
#define LIB_JPEGLI_BIT_WRITER_H_
#include <stdint.h>
#include <string.h>
#include "lib/jpegli/common.h"
#include "lib/jxl/base/byte_order.h"
#include "lib/jxl/base/compiler_specific.h"
namespace jpegli {
// Handles the packing of bits into output bytes.
struct JpegBitWriter {
j_compress_ptr cinfo;
uint8_t* data;
size_t len;
size_t pos;
size_t output_pos;
uint64_t put_buffer;
int free_bits;
bool healthy;
};
void JpegBitWriterInit(j_compress_ptr cinfo);
bool EmptyBitWriterBuffer(JpegBitWriter* bw);
void JumpToByteBoundary(JpegBitWriter* bw);
// Returns non-zero if and only if x has a zero byte, i.e. one of
// x & 0xff, x & 0xff00, ..., x & 0xff00000000000000 is zero.
static JXL_INLINE uint64_t HasZeroByte(uint64_t x) {
return (x - 0x0101010101010101ULL) & ~x & 0x8080808080808080ULL;
}
/**
* Writes the given byte to the output, writes an extra zero if byte is 0xFF.
*
* This method is "careless" - caller must make sure that there is enough
* space in the output buffer. Emits up to 2 bytes to buffer.
*/
static JXL_INLINE void EmitByte(JpegBitWriter* bw, int byte) {
bw->data[bw->pos++] = byte;
if (byte == 0xFF) bw->data[bw->pos++] = 0;
}
static JXL_INLINE void DischargeBitBuffer(JpegBitWriter* bw) {
// At this point we are ready to emit the bytes of put_buffer to the output.
// The JPEG format requires that after every 0xff byte in the entropy
// coded section, there is a zero byte, therefore we first check if any of
// the bytes of put_buffer is 0xFF.
if (HasZeroByte(~bw->put_buffer)) {
// We have a 0xFF byte somewhere, examine each byte and append a zero
// byte if necessary.
EmitByte(bw, (bw->put_buffer >> 56) & 0xFF);
EmitByte(bw, (bw->put_buffer >> 48) & 0xFF);
EmitByte(bw, (bw->put_buffer >> 40) & 0xFF);
EmitByte(bw, (bw->put_buffer >> 32) & 0xFF);
EmitByte(bw, (bw->put_buffer >> 24) & 0xFF);
EmitByte(bw, (bw->put_buffer >> 16) & 0xFF);
EmitByte(bw, (bw->put_buffer >> 8) & 0xFF);
EmitByte(bw, (bw->put_buffer >> 0) & 0xFF);
} else {
// We don't have any 0xFF bytes, output all 8 bytes without checking.
StoreBE64(bw->put_buffer, bw->data + bw->pos);
bw->pos += 8;
}
}
static JXL_INLINE void WriteBits(JpegBitWriter* bw, int nbits, uint64_t bits) {
// This is an optimization; if everything goes well,
// then |nbits| is positive; if non-existing Huffman symbol is going to be
// encoded, its length should be zero; later encoder could check the
// "health" of JpegBitWriter.
if (nbits == 0) {
bw->healthy = false;
return;
}
bw->free_bits -= nbits;
if (bw->free_bits < 0) {
bw->put_buffer <<= (bw->free_bits + nbits);
bw->put_buffer |= (bits >> -bw->free_bits);
DischargeBitBuffer(bw);
bw->free_bits += 64;
bw->put_buffer = nbits;
}
bw->put_buffer <<= nbits;
bw->put_buffer |= bits;
}
} // namespace jpegli
#endif // LIB_JPEGLI_BIT_WRITER_H_
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