1 files changed, 85 insertions, 0 deletions
diff --git a/modules/brotli/enc/write_bits.h b/modules/brotli/enc/write_bits.h
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+++ b/modules/brotli/enc/write_bits.h
@@ -0,0 +1,85 @@
+/* Copyright 2010 Google Inc. All Rights Reserved.
+
+   Distributed under MIT license.
+   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+/* Write bits into a byte array. */
+
+#ifndef BROTLI_ENC_WRITE_BITS_H_
+#define BROTLI_ENC_WRITE_BITS_H_
+
+#include "../common/platform.h"
+#include <brotli/types.h>
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+/*#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. */
+static BROTLI_INLINE void BrotliWriteBits(size_t n_bits,
+                                          uint64_t bits,
+                                          size_t* BROTLI_RESTRICT pos,
+                                          uint8_t* BROTLI_RESTRICT array) {
+#if defined(BROTLI_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 = (uint64_t)(*p);  /* Zero-extend 8 to 64 bits. */
+  BROTLI_LOG(("WriteBits  %2d  0x%08x%08x  %10d\n", (int)n_bits,
+      (uint32_t)(bits >> 32), (uint32_t)(bits & 0xFFFFFFFF),
+      (int)*pos));
+  BROTLI_DCHECK((bits >> n_bits) == 0);
+  BROTLI_DCHECK(n_bits <= 56);
+  v |= bits << (*pos & 7);
+  BROTLI_UNALIGNED_STORE64LE(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 size_t bits_reserved_in_first_byte = (*pos & 7);
+  size_t bits_left_to_write;
+  bits <<= bits_reserved_in_first_byte;
+  *array_pos++ |= (uint8_t)bits;
+  for (bits_left_to_write = n_bits + bits_reserved_in_first_byte;
+       bits_left_to_write >= 9;
+       bits_left_to_write -= 8) {
+    bits >>= 8;
+    *array_pos++ = (uint8_t)bits;
+  }
+  *array_pos = 0;
+  *pos += n_bits;
+#endif
+}
+
+static BROTLI_INLINE void BrotliWriteBitsPrepareStorage(
+    size_t pos, uint8_t* array) {
+  BROTLI_LOG(("WriteBitsPrepareStorage            %10d\n", (int)pos));
+  BROTLI_DCHECK((pos & 7) == 0);
+  array[pos >> 3] = 0;
+}
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}  /* extern "C" */
+#endif
+
+#endif  /* BROTLI_ENC_WRITE_BITS_H_ */