summaryrefslogtreecommitdiffstats
path: root/modules/brotli/enc/write_bits.h
diff options
context:
space:
mode:
Diffstat (limited to 'modules/brotli/enc/write_bits.h')
-rw-r--r--modules/brotli/enc/write_bits.h85
1 files changed, 85 insertions, 0 deletions
diff --git a/modules/brotli/enc/write_bits.h b/modules/brotli/enc/write_bits.h
new file mode 100644
index 000000000..36515a689
--- /dev/null
+++ 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_ */