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diff --git a/brotli/enc/write_bits.h b/brotli/enc/write_bits.h
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+// Copyright 2010 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.
+//
+// Write bits into a byte array.
+
+#ifndef BROTLI_ENC_WRITE_BITS_H_
+#define BROTLI_ENC_WRITE_BITS_H_
+
+#include <assert.h>
+#if defined(OS_MACOSX)
+  #include <machine/endian.h>
+#else
+  #include <endian.h>
+#endif
+#include <stdint.h>
+#include <stdio.h>
+
+#include "./port.h"
+
+namespace brotli {
+
+//#define BIT_WRITER_DEBUG
+
+// This function writes bits into bytes in increasing addresses, and within
+// a byte least-significant-bit first.
+//
+// The function can write up to 56 bits in one go with WriteBits
+// Example: let's assume that 3 bits (Rs below) have been written already:
+//
+// BYTE-0     BYTE+1       BYTE+2
+//
+// 0000 0RRR    0000 0000    0000 0000
+//
+// Now, we could write 5 or less bits in MSB by just sifting by 3
+// and OR'ing to BYTE-0.
+//
+// For n bits, we take the last 5 bits, OR that with high bits in BYTE-0,
+// and locate the rest in BYTE+1, BYTE+2, etc.
+inline void WriteBits(int n_bits,
+                      uint64_t bits,
+                      int * __restrict pos,
+                      uint8_t * __restrict array) {
+#ifdef BIT_WRITER_DEBUG
+  printf("WriteBits  %2d  0x%016llx  %10d\n", n_bits, bits, *pos);
+#endif
+#ifdef IS_LITTLE_ENDIAN
+  // This branch of the code can write up to 56 bits at a time,
+  // 7 bits are lost by being perhaps already in *p and at least
+  // 1 bit is needed to initialize the bit-stream ahead (i.e. if 7
+  // bits are in *p and we write 57 bits, then the next write will
+  // access a byte that was never initialized).
+  uint8_t *p = &array[*pos >> 3];
+  uint64_t v = *p;
+  v |= bits << (*pos & 7);
+  BROTLI_UNALIGNED_STORE64(p, v);  // Set some bits.
+  *pos += n_bits;
+#else
+  // implicit & 0xff is assumed for uint8_t arithmetics
+  uint8_t *array_pos = &array[*pos >> 3];
+  const int bits_reserved_in_first_byte = (*pos & 7);
+  bits <<= bits_reserved_in_first_byte;
+  *array_pos++ |= bits;
+  for (int bits_left_to_write = n_bits - 8 + bits_reserved_in_first_byte;
+       bits_left_to_write >= 1;
+       bits_left_to_write -= 8) {
+    bits >>= 8;
+    *array_pos++ = bits;
+  }
+  *array_pos = 0;
+  *pos += n_bits;
+#endif
+}
+
+inline void WriteBitsPrepareStorage(int pos, uint8_t *array) {
+#ifdef BIT_WRITER_DEBUG
+  printf("WriteBitsPrepareStorage            %10d\n", pos);
+#endif
+  assert((pos & 7) == 0);
+  array[pos >> 3] = 0;
+}
+
+}  // namespace brotli
+
+#endif  // BROTLI_ENC_WRITE_BITS_H_