text: /* Ppmd.h -- PPMD codec common code
  2010-03-12 : Igor Pavlov : Public domain
  This code is based on PPMd var.H (2001): Dmitry Shkarin : Public domain */
  
  #ifndef __PPMD_H
  #define __PPMD_H
  
  #include "Types.h"
  #include "CpuArch.h"
  
  EXTERN_C_BEGIN
  
  #ifdef MY_CPU_32BIT
    #define PPMD_32BIT
  #endif
  
  #define PPMD_INT_BITS 7
  #define PPMD_PERIOD_BITS 7
  #define PPMD_BIN_SCALE (1 << (PPMD_INT_BITS + PPMD_PERIOD_BITS))
  
  #define PPMD_GET_MEAN_SPEC(summ, shift, round) (((summ) + (1 << ((shift) - (round)))) >> (shift))
  #define PPMD_GET_MEAN(summ) PPMD_GET_MEAN_SPEC((summ), PPMD_PERIOD_BITS, 2)
  #define PPMD_UPDATE_PROB_0(prob) ((prob) + (1 << PPMD_INT_BITS) - PPMD_GET_MEAN(prob))
  #define PPMD_UPDATE_PROB_1(prob) ((prob) - PPMD_GET_MEAN(prob))
  
  #define PPMD_N1 4
  #define PPMD_N2 4
  #define PPMD_N3 4
  #define PPMD_N4 ((128 + 3 - 1 * PPMD_N1 - 2 * PPMD_N2 - 3 * PPMD_N3) / 4)
  #define PPMD_NUM_INDEXES (PPMD_N1 + PPMD_N2 + PPMD_N3 + PPMD_N4)
  
  #pragma pack(push,1)
  
  /* SEE-contexts for PPM-contexts with masked symbols */
  typedef struct
  {
    UInt16 Summ; /* Freq */
    Byte Shift;  /* Speed of Freq change; low Shift is for fast change */
    Byte Count;  /* Count to next change of Shift */
  } CPpmd_See;
  
  #define Ppmd_See_Update(p)  if ((p)->Shift < PPMD_PERIOD_BITS && --(p)->Count == 0) \
      { (p)->Summ <<= 1; (p)->Count = (Byte)(3 << (p)->Shift++); }
  
  typedef struct
  {
    Byte Symbol;
    Byte Freq;
    UInt16 SuccessorLow;
    UInt16 SuccessorHigh;
  } CPpmd_State;
  
  #pragma pack(pop)
  
  typedef
    #ifdef PPMD_32BIT
      CPpmd_State *
    #else
      UInt32
    #endif
    CPpmd_State_Ref;
  
  typedef
    #ifdef PPMD_32BIT
      void *
    #else
      UInt32
    #endif
    CPpmd_Void_Ref;
  
  typedef
    #ifdef PPMD_32BIT
      Byte *
    #else
      UInt32
    #endif
    CPpmd_Byte_Ref;
  
  #define PPMD_SetAllBitsIn256Bytes(p) \
    { unsigned i; for (i = 0; i < 256 / sizeof(p[0]); i += 8) { \
    p[i+7] = p[i+6] = p[i+5] = p[i+4] = p[i+3] = p[i+2] = p[i+1] = p[i+0] = ~(size_t)0; }}
  
  EXTERN_C_END
   
  #endif
  