Update from https://crrev.com/318214

third_party/brotli/dec/bit_reader.h

+/* Copyright 2013 Google Inc. All Rights Reserved.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+   Bit reading helpers
+*/
+
+#ifndef BROTLI_DEC_BIT_READER_H_
+#define BROTLI_DEC_BIT_READER_H_
+
+#include <string.h>
+#include "./streams.h"
+#include "./types.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+#define BROTLI_MAX_NUM_BIT_READ   25
+#define BROTLI_READ_SIZE          4096
+#define BROTLI_IBUF_SIZE          (2 * BROTLI_READ_SIZE + 32)
+#define BROTLI_IBUF_MASK          (2 * BROTLI_READ_SIZE - 1)
+
+#define UNALIGNED_COPY64(dst, src) memcpy(dst, src, 8)
+#define UNALIGNED_MOVE64(dst, src) memmove(dst, src, 8)
+
+static const uint32_t kBitMask[BROTLI_MAX_NUM_BIT_READ] = {
+  0, 1, 3, 7, 15, 31, 63, 127, 255, 511, 1023, 2047, 4095, 8191, 16383, 32767,
+  65535, 131071, 262143, 524287, 1048575, 2097151, 4194303, 8388607, 16777215
+};
+
+typedef struct {
+  /* Input byte buffer, consist of a ringbuffer and a "slack" region where */
+  /* bytes from the start of the ringbuffer are copied. */
+  uint8_t buf_[BROTLI_IBUF_SIZE];
+  uint8_t*    buf_ptr_;      /* next input will write here */
+  BrotliInput input_;        /* input callback */
+  uint64_t    val_;          /* pre-fetched bits */
+  uint32_t    pos_;          /* byte position in stream */
+  uint32_t    bit_pos_;      /* current bit-reading position in val_ */
+  uint32_t    bit_end_pos_;  /* bit-reading end position from LSB of val_ */
+  int         eos_;          /* input stream is finished */
+} BrotliBitReader;
+
+int BrotliInitBitReader(BrotliBitReader* const br, BrotliInput input);
+
+/* Return the prefetched bits, so they can be looked up. */
+static BROTLI_INLINE uint32_t BrotliPrefetchBits(BrotliBitReader* const br) {
+  return (uint32_t)(br->val_ >> br->bit_pos_);
+}
+
+/* For jumping over a number of bits in the bit stream when accessed with */
+/* BrotliPrefetchBits and BrotliFillBitWindow. */
+static BROTLI_INLINE void BrotliSetBitPos(BrotliBitReader* const br,
+                                          uint32_t val) {
+#ifdef BROTLI_DECODE_DEBUG
+  uint32_t n_bits = val - br->bit_pos_;
+  const uint32_t bval = (uint32_t)(br->val_ >> br->bit_pos_) & kBitMask[n_bits];
+  printf("[BrotliReadBits]  %010d %2d  val: %6x\n",
+         (br->pos_ << 3) + br->bit_pos_ - 64, n_bits, bval);
+#endif
+  br->bit_pos_ = val;
+}
+
+/* Reload up to 64 bits byte-by-byte */
+static BROTLI_INLINE void ShiftBytes(BrotliBitReader* const br) {
+  while (br->bit_pos_ >= 8) {
+    br->val_ >>= 8;
+    br->val_ |= ((uint64_t)br->buf_[br->pos_ & BROTLI_IBUF_MASK]) << 56;
+    ++br->pos_;
+    br->bit_pos_ -= 8;
+    br->bit_end_pos_ -= 8;
+  }
+}
+
+/* Fills up the input ringbuffer by calling the input callback.
+
+   Does nothing if there are at least 32 bytes present after current position.
+
+   Returns 0 if either:
+    - the input callback returned an error, or
+    - there is no more input and the position is past the end of the stream.
+
+   After encountering the end of the input stream, 32 additional zero bytes are
+   copied to the ringbuffer, therefore it is safe to call this function after
+   every 32 bytes of input is read.
+*/
+static BROTLI_INLINE int BrotliReadMoreInput(BrotliBitReader* const br) {
+  if (br->bit_end_pos_ > 256) {
+    return 1;
+  } else if (br->eos_) {
+    return br->bit_pos_ <= br->bit_end_pos_;
+  } else {
+    uint8_t* dst = br->buf_ptr_;
+    int bytes_read = BrotliRead(br->input_, dst, BROTLI_READ_SIZE);
+    if (bytes_read < 0) {
+      return 0;
+    }
+    if (bytes_read < BROTLI_READ_SIZE) {
+      br->eos_ = 1;
+      /* Store 32 bytes of zero after the stream end. */
+#if (defined(__x86_64__) || defined(_M_X64))
+      *(uint64_t*)(dst + bytes_read) = 0;
+      *(uint64_t*)(dst + bytes_read + 8) = 0;
+      *(uint64_t*)(dst + bytes_read + 16) = 0;
+      *(uint64_t*)(dst + bytes_read + 24) = 0;
+#else
+      memset(dst + bytes_read, 0, 32);
+#endif
+    }
+    if (dst == br->buf_) {
+      /* Copy the head of the ringbuffer to the slack region. */
+#if (defined(__x86_64__) || defined(_M_X64))
+      UNALIGNED_COPY64(br->buf_ + BROTLI_IBUF_SIZE - 32, br->buf_);
+      UNALIGNED_COPY64(br->buf_ + BROTLI_IBUF_SIZE - 24, br->buf_ + 8);
+      UNALIGNED_COPY64(br->buf_ + BROTLI_IBUF_SIZE - 16, br->buf_ + 16);
+      UNALIGNED_COPY64(br->buf_ + BROTLI_IBUF_SIZE - 8, br->buf_ + 24);
+#else
+      memcpy(br->buf_ + (BROTLI_READ_SIZE << 1), br->buf_, 32);
+#endif
+      br->buf_ptr_ = br->buf_ + BROTLI_READ_SIZE;
+    } else {
+      br->buf_ptr_ = br->buf_;
+    }
+    br->bit_end_pos_ += ((uint32_t)bytes_read << 3);
+    return 1;
+  }
+}
+
+/* Advances the Read buffer by 5 bytes to make room for reading next 24 bits. */
+static BROTLI_INLINE void BrotliFillBitWindow(BrotliBitReader* const br) {
+  if (br->bit_pos_ >= 40) {
+#if (defined(__x86_64__) || defined(_M_X64))
+    br->val_ >>= 40;
+    /* The expression below needs a little-endian arch to work correctly. */
+    /* This gives a large speedup for decoding speed. */
+    br->val_ |= *(const uint64_t*)(
+        br->buf_ + (br->pos_ & BROTLI_IBUF_MASK)) << 24;
+    br->pos_ += 5;
+    br->bit_pos_ -= 40;
+    br->bit_end_pos_ -= 40;
+#else
+    ShiftBytes(br);
+#endif
+  }
+}
+
+/* Reads the specified number of bits from Read Buffer. */
+static BROTLI_INLINE uint32_t BrotliReadBits(
+    BrotliBitReader* const br, int n_bits) {
+  uint32_t val;
+  BrotliFillBitWindow(br);
+  val = (uint32_t)(br->val_ >> br->bit_pos_) & kBitMask[n_bits];
+#ifdef BROTLI_DECODE_DEBUG
+  printf("[BrotliReadBits]  %010d %2d  val: %6x\n",
+         (br->pos_ << 3) + br->bit_pos_ - 64, n_bits, val);
+#endif
+  br->bit_pos_ += (uint32_t)n_bits;
+  return val;
+}
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    /* extern "C" */
+#endif
+
+#endif  /* BROTLI_DEC_BIT_READER_H_ */