/* 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)
 
 /* 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;
 
 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