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   1 /*
   2  * lzms_common.h
   3  *
   4  * Declarations shared between LZMS compression and decompression.
   5  */
   6
   7 #ifndef _LZMS_COMMON_H
   8 #define _LZMS_COMMON_H
   9
  10 #include "wimlib/compiler.h"
  11 #include "wimlib/lzms_constants.h"
  12 #include "wimlib/types.h"
  13
  14 /* Offset slot tables  */
  15 extern const u32 lzms_offset_slot_base[LZMS_MAX_NUM_OFFSET_SYMS + 1];
  16 extern const u8 lzms_extra_offset_bits[LZMS_MAX_NUM_OFFSET_SYMS];
  17
  18 /* Length slot tables  */
  19 extern const u32 lzms_length_slot_base[LZMS_NUM_LENGTH_SYMS + 1];
  20 extern const u8 lzms_extra_length_bits[LZMS_NUM_LENGTH_SYMS];
  21
  22 extern unsigned
  23 lzms_get_slot(u32 value, const u32 slot_base_tab[], unsigned num_slots);
  24
  25 /* Return the offset slot for the specified offset  */
  26 static inline unsigned
  27 lzms_get_offset_slot(u32 offset)
  28 {
  29         return lzms_get_slot(offset, lzms_offset_slot_base, LZMS_MAX_NUM_OFFSET_SYMS);
  30 }
  31
  32 /* Return the length slot for the specified length  */
  33 static inline unsigned
  34 lzms_get_length_slot(u32 length)
  35 {
  36         return lzms_get_slot(length, lzms_length_slot_base, LZMS_NUM_LENGTH_SYMS);
  37 }
  38
  39 extern unsigned
  40 lzms_get_num_offset_slots(size_t uncompressed_size);
  41
  42
  43 /* Probability entry for use by the range coder when in a specific state  */
  44 struct lzms_probability_entry {
  45
  46         /* The number of zeroes in the most recent LZMS_PROBABILITY_DENOMINATOR
  47          * bits that have been decoded or encoded using this probability entry.
  48          * The probability of the next bit being 0 is this value over
  49          * LZMS_PROBABILITY_DENOMINATOR, except for the cases where this would
  50          * imply 0% or 100% probability.  */
  51         u32 num_recent_zero_bits;
  52
  53         /* The most recent LZMS_PROBABILITY_DENOMINATOR bits that have been
  54          * coded using this probability entry.  The bits are ordered such that
  55          * low order is newest and high order is oldest.  */
  56         u64 recent_bits;
  57 };
  58
  59 extern void
  60 lzms_init_probability_entries(struct lzms_probability_entry *entries, size_t count);
  61
  62 /* Given a decoded or encoded bit, update the probability entry.  */
  63 static inline void
  64 lzms_update_probability_entry(struct lzms_probability_entry *entry, int bit)
  65 {
  66         BUILD_BUG_ON(LZMS_PROBABILITY_DENOMINATOR != sizeof(entry->recent_bits) * 8);
  67
  68         s32 delta_zero_bits = (s32)(entry->recent_bits >>
  69                                     (LZMS_PROBABILITY_DENOMINATOR - 1)) - bit;
  70
  71         entry->num_recent_zero_bits += delta_zero_bits;
  72         entry->recent_bits = (entry->recent_bits << 1) | bit;
  73 }
  74
  75 /* Given a probability entry, return the chance out of
  76  * LZMS_PROBABILITY_DENOMINATOR that the next decoded bit will be a 0.  */
  77 static inline u32
  78 lzms_get_probability(const struct lzms_probability_entry *prob_entry)
  79 {
  80         u32 prob = prob_entry->num_recent_zero_bits;
  81
  82         /* 0% and 100% probabilities aren't allowed.  */
  83         if (prob == 0)
  84                 prob++;
  85         else if (prob == LZMS_PROBABILITY_DENOMINATOR)
  86                 prob--;
  87         return prob;
  88 }
  89
  90 extern void
  91 lzms_init_symbol_frequencies(u32 freqs[], unsigned num_syms);
  92
  93 extern void
  94 lzms_dilute_symbol_frequencies(u32 freqs[], unsigned num_syms);
  95
  96 /* Pre/post-processing  */
  97 extern void
  98 lzms_x86_filter(u8 data[], s32 size, s32 last_target_usages[], bool undo);
  99
 100 #endif /* _LZMS_COMMON_H */