diff options
Diffstat (limited to 'drivers/webp/enc/backward_references.h')
| -rw-r--r-- | drivers/webp/enc/backward_references.h | 74 |
1 files changed, 67 insertions, 7 deletions
diff --git a/drivers/webp/enc/backward_references.h b/drivers/webp/enc/backward_references.h index e1c75f04f9..91c03361ed 100644 --- a/drivers/webp/enc/backward_references.h +++ b/drivers/webp/enc/backward_references.h @@ -1,10 +1,8 @@ // Copyright 2012 Google Inc. All Rights Reserved. // -// Use of this source code is governed by a BSD-style license -// that can be found in the COPYING file in the root of the source -// tree. An additional intellectual property rights grant can be found -// in the file PATENTS. All contributing project authors may -// be found in the AUTHORS file in the root of the source tree. +// This code is licensed under the same terms as WebM: +// Software License Agreement: http://www.webmproject.org/license/software/ +// Additional IP Rights Grant: http://www.webmproject.org/license/additional/ // ----------------------------------------------------------------------------- // // Author: Jyrki Alakuijala (jyrki@google.com) @@ -18,7 +16,7 @@ #include "../webp/types.h" #include "../webp/format_constants.h" -#ifdef __cplusplus +#if defined(__cplusplus) || defined(c_plusplus) extern "C" { #endif @@ -31,6 +29,68 @@ extern "C" { (NUM_LITERAL_CODES + NUM_LENGTH_CODES + (1 << MAX_COLOR_CACHE_BITS)) // ----------------------------------------------------------------------------- +// PrefixEncode() + +// use GNU builtins where available. +#if defined(__GNUC__) && \ + ((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4) +static WEBP_INLINE int BitsLog2Floor(uint32_t n) { + return n == 0 ? -1 : 31 ^ __builtin_clz(n); +} +#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_IX86)) +#include <intrin.h> +#pragma intrinsic(_BitScanReverse) + +static WEBP_INLINE int BitsLog2Floor(uint32_t n) { + unsigned long first_set_bit; + return _BitScanReverse(&first_set_bit, n) ? first_set_bit : -1; +} +#else +static WEBP_INLINE int BitsLog2Floor(uint32_t n) { + int log = 0; + uint32_t value = n; + int i; + + if (value == 0) return -1; + for (i = 4; i >= 0; --i) { + const int shift = (1 << i); + const uint32_t x = value >> shift; + if (x != 0) { + value = x; + log += shift; + } + } + return log; +} +#endif + +static WEBP_INLINE int VP8LBitsLog2Ceiling(uint32_t n) { + const int floor = BitsLog2Floor(n); + if (n == (n & ~(n - 1))) // zero or a power of two. + return floor; + else + return floor + 1; +} + +// Splitting of distance and length codes into prefixes and +// extra bits. The prefixes are encoded with an entropy code +// while the extra bits are stored just as normal bits. +static WEBP_INLINE void PrefixEncode(int distance, int* const code, + int* const extra_bits_count, + int* const extra_bits_value) { + // Collect the two most significant bits where the highest bit is 1. + const int highest_bit = BitsLog2Floor(--distance); + // & 0x3f is to make behavior well defined when highest_bit + // does not exist or is the least significant bit. + const int second_highest_bit = + (distance >> ((highest_bit - 1) & 0x3f)) & 1; + *extra_bits_count = (highest_bit > 0) ? (highest_bit - 1) : 0; + *extra_bits_value = distance & ((1 << *extra_bits_count) - 1); + *code = (highest_bit > 0) ? (2 * highest_bit + second_highest_bit) + : (highest_bit == 0) ? 1 : 0; +} + +// ----------------------------------------------------------------------------- // PixOrCopy enum Mode { @@ -145,7 +205,7 @@ int VP8LCalculateEstimateForCacheSize(const uint32_t* const argb, int xsize, int ysize, int* const best_cache_bits); -#ifdef __cplusplus +#if defined(__cplusplus) || defined(c_plusplus) } #endif |