xref: /aosp_15_r20/external/lzma/C/Ppmd7.c (revision f6dc9357d832569d4d1f5d24eacdb3935a1ae8e6)

/* Ppmd7.c -- PPMdH codec
2023-09-07 : Igor Pavlov : Public domain
This code is based on PPMd var.H (2001): Dmitry Shkarin : Public domain */

#include "Precomp.h"

#include <string.h>

#include "Ppmd7.h"

/* define PPMD7_ORDER_0_SUPPPORT to suport order-0 mode, unsupported by orignal PPMd var.H. code */
// #define PPMD7_ORDER_0_SUPPPORT

MY_ALIGN(16)
static const Byte PPMD7_kExpEscape[16] = { 25, 14, 9, 7, 5, 5, 4, 4, 4, 3, 3, 3, 2, 2, 2, 2 };
MY_ALIGN(16)
static const UInt16 PPMD7_kInitBinEsc[] = { 0x3CDD, 0x1F3F, 0x59BF, 0x48F3, 0x64A1, 0x5ABC, 0x6632, 0x6051};

#define MAX_FREQ 124
#define UNIT_SIZE 12

#define U2B(nu) ((UInt32)(nu) * UNIT_SIZE)
#define U2I(nu) (p->Units2Indx[(size_t)(nu) - 1])
#define I2U(indx) ((unsigned)p->Indx2Units[indx])
#define I2U_UInt16(indx) ((UInt16)p->Indx2Units[indx])

#define REF(ptr) Ppmd_GetRef(p, ptr)

#define STATS_REF(ptr) ((CPpmd_State_Ref)REF(ptr))

#define CTX(ref) ((CPpmd7_Context *)Ppmd7_GetContext(p, ref))
#define STATS(ctx) Ppmd7_GetStats(p, ctx)
#define ONE_STATE(ctx) Ppmd7Context_OneState(ctx)
#define SUFFIX(ctx) CTX((ctx)->Suffix)

typedef CPpmd7_Context * PPMD7_CTX_PTR;

struct CPpmd7_Node_;

typedef Ppmd_Ref_Type(struct CPpmd7_Node_) CPpmd7_Node_Ref;

typedef struct CPpmd7_Node_
{
  UInt16 Stamp; /* must be at offset 0 as CPpmd7_Context::NumStats. Stamp=0 means free */
  UInt16 NU;
  CPpmd7_Node_Ref Next; /* must be at offset >= 4 */
  CPpmd7_Node_Ref Prev;
} CPpmd7_Node;

#define NODE(r)  Ppmd_GetPtr_Type(p, r, CPpmd7_Node)

void Ppmd7_Construct(CPpmd7 *p)
{
  unsigned i, k, m;

  p->Base = NULL;

  for (i = 0, k = 0; i < PPMD_NUM_INDEXES; i++)
  {
    unsigned step = (i >= 12 ? 4 : (i >> 2) + 1);
    do { p->Units2Indx[k++] = (Byte)i; } while (--step);
    p->Indx2Units[i] = (Byte)k;
  }

  p->NS2BSIndx[0] = (0 << 1);
  p->NS2BSIndx[1] = (1 << 1);
  memset(p->NS2BSIndx + 2, (2 << 1), 9);
  memset(p->NS2BSIndx + 11, (3 << 1), 256 - 11);

  for (i = 0; i < 3; i++)
    p->NS2Indx[i] = (Byte)i;

  for (m = i, k = 1; i < 256; i++)
  {
    p->NS2Indx[i] = (Byte)m;
    if (--k == 0)
      k = (++m) - 2;
  }

  memcpy(p->ExpEscape, PPMD7_kExpEscape, 16);
}


void Ppmd7_Free(CPpmd7 *p, ISzAllocPtr alloc)
{
  ISzAlloc_Free(alloc, p->Base);
  p->Size = 0;
  p->Base = NULL;
}


BoolInt Ppmd7_Alloc(CPpmd7 *p, UInt32 size, ISzAllocPtr alloc)
{
  if (!p->Base || p->Size != size)
  {
    Ppmd7_Free(p, alloc);
    p->AlignOffset = (4 - size) & 3;
    if ((p->Base = (Byte *)ISzAlloc_Alloc(alloc, p->AlignOffset + size)) == NULL)
      return False;
    p->Size = size;
  }
  return True;
}



// ---------- Internal Memory Allocator ----------

/* We can use CPpmd7_Node in list of free units (as in Ppmd8)
   But we still need one additional list walk pass in Ppmd7_GlueFreeBlocks().
   So we use simple CPpmd_Void_Ref instead of CPpmd7_Node in Ppmd7_InsertNode() / Ppmd7_RemoveNode()
*/

#define EMPTY_NODE 0


static void Ppmd7_InsertNode(CPpmd7 *p, void *node, unsigned indx)
{
  *((CPpmd_Void_Ref *)node) = p->FreeList[indx];
  // ((CPpmd7_Node *)node)->Next = (CPpmd7_Node_Ref)p->FreeList[indx];

  p->FreeList[indx] = REF(node);

}


static void *Ppmd7_RemoveNode(CPpmd7 *p, unsigned indx)
{
  CPpmd_Void_Ref *node = (CPpmd_Void_Ref *)Ppmd7_GetPtr(p, p->FreeList[indx]);
  p->FreeList[indx] = *node;
  // CPpmd7_Node *node = NODE((CPpmd7_Node_Ref)p->FreeList[indx]);
  // p->FreeList[indx] = node->Next;
  return node;
}


static void Ppmd7_SplitBlock(CPpmd7 *p, void *ptr, unsigned oldIndx, unsigned newIndx)
{
  unsigned i, nu = I2U(oldIndx) - I2U(newIndx);
  ptr = (Byte *)ptr + U2B(I2U(newIndx));
  if (I2U(i = U2I(nu)) != nu)
  {
    unsigned k = I2U(--i);
    Ppmd7_InsertNode(p, ((Byte *)ptr) + U2B(k), nu - k - 1);
  }
  Ppmd7_InsertNode(p, ptr, i);
}


/* we use CPpmd7_Node_Union union to solve XLC -O2 strict pointer aliasing problem */

typedef union
{
  CPpmd7_Node     Node;
  CPpmd7_Node_Ref NextRef;
} CPpmd7_Node_Union;

/* Original PPmdH (Ppmd7) code uses doubly linked list in Ppmd7_GlueFreeBlocks()
   we use single linked list similar to Ppmd8 code */


static void Ppmd7_GlueFreeBlocks(CPpmd7 *p)
{
  /*
  we use first UInt16 field of 12-bytes UNITs as record type stamp
    CPpmd_State    { Byte Symbol; Byte Freq; : Freq != 0
    CPpmd7_Context { UInt16 NumStats;        : NumStats != 0
    CPpmd7_Node    { UInt16 Stamp            : Stamp == 0 for free record
                                             : Stamp == 1 for head record and guard
    Last 12-bytes UNIT in array is always contains 12-bytes order-0 CPpmd7_Context record.
  */
  CPpmd7_Node_Ref head, n = 0;

  p->GlueCount = 255;


  /* we set guard NODE at LoUnit */
  if (p->LoUnit != p->HiUnit)
    ((CPpmd7_Node *)(void *)p->LoUnit)->Stamp = 1;

  {
    /* Create list of free blocks.
       We still need one additional list walk pass before Glue. */
    unsigned i;
    for (i = 0; i < PPMD_NUM_INDEXES; i++)
    {
      const UInt16 nu = I2U_UInt16(i);
      CPpmd7_Node_Ref next = (CPpmd7_Node_Ref)p->FreeList[i];
      p->FreeList[i] = 0;
      while (next != 0)
      {
        /* Don't change the order of the following commands: */
        CPpmd7_Node_Union *un = (CPpmd7_Node_Union *)NODE(next);
        const CPpmd7_Node_Ref tmp = next;
        next = un->NextRef;
        un->Node.Stamp = EMPTY_NODE;
        un->Node.NU = nu;
        un->Node.Next = n;
        n = tmp;
      }
    }
  }

  head = n;
  /* Glue and Fill must walk the list in same direction */
  {
    /* Glue free blocks */
    CPpmd7_Node_Ref *prev = &head;
    while (n)
    {
      CPpmd7_Node *node = NODE(n);
      UInt32 nu = node->NU;
      n = node->Next;
      if (nu == 0)
      {
        *prev = n;
        continue;
      }
      prev = &node->Next;
      for (;;)
      {
        CPpmd7_Node *node2 = node + nu;
        nu += node2->NU;
        if (node2->Stamp != EMPTY_NODE || nu >= 0x10000)
          break;
        node->NU = (UInt16)nu;
        node2->NU = 0;
      }
    }
  }

  /* Fill lists of free blocks */
  for (n = head; n != 0;)
  {
    CPpmd7_Node *node = NODE(n);
    UInt32 nu = node->NU;
    unsigned i;
    n = node->Next;
    if (nu == 0)
      continue;
    for (; nu > 128; nu -= 128, node += 128)
      Ppmd7_InsertNode(p, node, PPMD_NUM_INDEXES - 1);
    if (I2U(i = U2I(nu)) != nu)
    {
      unsigned k = I2U(--i);
      Ppmd7_InsertNode(p, node + k, (unsigned)nu - k - 1);
    }
    Ppmd7_InsertNode(p, node, i);
  }
}


Z7_NO_INLINE
static void *Ppmd7_AllocUnitsRare(CPpmd7 *p, unsigned indx)
{
  unsigned i;

  if (p->GlueCount == 0)
  {
    Ppmd7_GlueFreeBlocks(p);
    if (p->FreeList[indx] != 0)
      return Ppmd7_RemoveNode(p, indx);
  }

  i = indx;

  do
  {
    if (++i == PPMD_NUM_INDEXES)
    {
      UInt32 numBytes = U2B(I2U(indx));
      Byte *us = p->UnitsStart;
      p->GlueCount--;
      return ((UInt32)(us - p->Text) > numBytes) ? (p->UnitsStart = us - numBytes) : NULL;
    }
  }
  while (p->FreeList[i] == 0);

  {
    void *block = Ppmd7_RemoveNode(p, i);
    Ppmd7_SplitBlock(p, block, i, indx);
    return block;
  }
}


static void *Ppmd7_AllocUnits(CPpmd7 *p, unsigned indx)
{
  if (p->FreeList[indx] != 0)
    return Ppmd7_RemoveNode(p, indx);
  {
    UInt32 numBytes = U2B(I2U(indx));
    Byte *lo = p->LoUnit;
    if ((UInt32)(p->HiUnit - lo) >= numBytes)
    {
      p->LoUnit = lo + numBytes;
      return lo;
    }
  }
  return Ppmd7_AllocUnitsRare(p, indx);
}


#define MEM_12_CPY(dest, src, num) \
  { UInt32 *d = (UInt32 *)(dest); \
    const UInt32 *z = (const UInt32 *)(src); \
    unsigned n = (num); \
    do { \
      d[0] = z[0]; \
      d[1] = z[1]; \
      d[2] = z[2]; \
      z += 3; \
      d += 3; \
    } while (--n); \
  }


/*
static void *ShrinkUnits(CPpmd7 *p, void *oldPtr, unsigned oldNU, unsigned newNU)
{
  unsigned i0 = U2I(oldNU);
  unsigned i1 = U2I(newNU);
  if (i0 == i1)
    return oldPtr;
  if (p->FreeList[i1] != 0)
  {
    void *ptr = Ppmd7_RemoveNode(p, i1);
    MEM_12_CPY(ptr, oldPtr, newNU)
    Ppmd7_InsertNode(p, oldPtr, i0);
    return ptr;
  }
  Ppmd7_SplitBlock(p, oldPtr, i0, i1);
  return oldPtr;
}
*/


#define SUCCESSOR(p) Ppmd_GET_SUCCESSOR(p)
static void SetSuccessor(CPpmd_State *p, CPpmd_Void_Ref v)
{
  Ppmd_SET_SUCCESSOR(p, v)
}



Z7_NO_INLINE
static
void Ppmd7_RestartModel(CPpmd7 *p)
{
  unsigned i, k;

  memset(p->FreeList, 0, sizeof(p->FreeList));

  p->Text = p->Base + p->AlignOffset;
  p->HiUnit = p->Text + p->Size;
  p->LoUnit = p->UnitsStart = p->HiUnit - p->Size / 8 / UNIT_SIZE * 7 * UNIT_SIZE;
  p->GlueCount = 0;

  p->OrderFall = p->MaxOrder;
  p->RunLength = p->InitRL = -(Int32)((p->MaxOrder < 12) ? p->MaxOrder : 12) - 1;
  p->PrevSuccess = 0;

  {
    CPpmd7_Context *mc = (PPMD7_CTX_PTR)(void *)(p->HiUnit -= UNIT_SIZE); /* AllocContext(p); */
    CPpmd_State *s = (CPpmd_State *)p->LoUnit; /* Ppmd7_AllocUnits(p, PPMD_NUM_INDEXES - 1); */

    p->LoUnit += U2B(256 / 2);
    p->MaxContext = p->MinContext = mc;
    p->FoundState = s;

    mc->NumStats = 256;
    mc->Union2.SummFreq = 256 + 1;
    mc->Union4.Stats = REF(s);
    mc->Suffix = 0;

    for (i = 0; i < 256; i++, s++)
    {
      s->Symbol = (Byte)i;
      s->Freq = 1;
      SetSuccessor(s, 0);
    }

    #ifdef PPMD7_ORDER_0_SUPPPORT
    if (p->MaxOrder == 0)
    {
      CPpmd_Void_Ref r = REF(mc);
      s = p->FoundState;
      for (i = 0; i < 256; i++, s++)
        SetSuccessor(s, r);
      return;
    }
    #endif
  }

  for (i = 0; i < 128; i++)



    for (k = 0; k < 8; k++)
    {
      unsigned m;
      UInt16 *dest = p->BinSumm[i] + k;
      const UInt16 val = (UInt16)(PPMD_BIN_SCALE - PPMD7_kInitBinEsc[k] / (i + 2));
      for (m = 0; m < 64; m += 8)
        dest[m] = val;
    }


  for (i = 0; i < 25; i++)
  {

    CPpmd_See *s = p->See[i];



    unsigned summ = ((5 * i + 10) << (PPMD_PERIOD_BITS - 4));
    for (k = 0; k < 16; k++, s++)
    {
      s->Summ = (UInt16)summ;
      s->Shift = (PPMD_PERIOD_BITS - 4);
      s->Count = 4;
    }
  }

  p->DummySee.Summ = 0; /* unused */
  p->DummySee.Shift = PPMD_PERIOD_BITS;
  p->DummySee.Count = 64; /* unused */
}


void Ppmd7_Init(CPpmd7 *p, unsigned maxOrder)
{
  p->MaxOrder = maxOrder;

  Ppmd7_RestartModel(p);
}



/*
  Ppmd7_CreateSuccessors()
  It's called when (FoundState->Successor) is RAW-Successor,
  that is the link to position in Raw text.
  So we create Context records and write the links to
  FoundState->Successor and to identical RAW-Successors in suffix
  contexts of MinContex.

  The function returns:
  if (OrderFall == 0) then MinContext is already at MAX order,
    { return pointer to new or existing context of same MAX order }
  else
    { return pointer to new real context that will be (Order+1) in comparison with MinContext

  also it can return pointer to real context of same order,
*/

Z7_NO_INLINE
static PPMD7_CTX_PTR Ppmd7_CreateSuccessors(CPpmd7 *p)
{
  PPMD7_CTX_PTR c = p->MinContext;
  CPpmd_Byte_Ref upBranch = (CPpmd_Byte_Ref)SUCCESSOR(p->FoundState);
  Byte newSym, newFreq;
  unsigned numPs = 0;
  CPpmd_State *ps[PPMD7_MAX_ORDER];

  if (p->OrderFall != 0)
    ps[numPs++] = p->FoundState;

  while (c->Suffix)
  {
    CPpmd_Void_Ref successor;
    CPpmd_State *s;
    c = SUFFIX(c);


    if (c->NumStats != 1)
    {
      Byte sym = p->FoundState->Symbol;
      for (s = STATS(c); s->Symbol != sym; s++);

    }
    else
    {
      s = ONE_STATE(c);

    }
    successor = SUCCESSOR(s);
    if (successor != upBranch)
    {
      // (c) is real record Context here,
      c = CTX(successor);
      if (numPs == 0)
      {
        // (c) is real record MAX Order Context here,
        // So we don't need to create any new contexts.
        return c;
      }
      break;
    }
    ps[numPs++] = s;
  }

  // All created contexts will have single-symbol with new RAW-Successor
  // All new RAW-Successors will point to next position in RAW text
  // after FoundState->Successor

  newSym = *(const Byte *)Ppmd7_GetPtr(p, upBranch);
  upBranch++;


  if (c->NumStats == 1)
    newFreq = ONE_STATE(c)->Freq;
  else
  {
    UInt32 cf, s0;
    CPpmd_State *s;
    for (s = STATS(c); s->Symbol != newSym; s++);
    cf = (UInt32)s->Freq - 1;
    s0 = (UInt32)c->Union2.SummFreq - c->NumStats - cf;
    /*
      cf - is frequency of symbol that will be Successor in new context records.
      s0 - is commulative frequency sum of another symbols from parent context.
      max(newFreq)= (s->Freq + 1), when (s0 == 1)
      we have requirement (Ppmd7Context_OneState()->Freq <= 128) in BinSumm[]
      so (s->Freq < 128) - is requirement for multi-symbol contexts
    */
    newFreq = (Byte)(1 + ((2 * cf <= s0) ? (5 * cf > s0) : (2 * cf + s0 - 1) / (2 * s0) + 1));
  }

  // Create new single-symbol contexts from low order to high order in loop

  do
  {
    PPMD7_CTX_PTR c1;
    /* = AllocContext(p); */
    if (p->HiUnit != p->LoUnit)
      c1 = (PPMD7_CTX_PTR)(void *)(p->HiUnit -= UNIT_SIZE);
    else if (p->FreeList[0] != 0)
      c1 = (PPMD7_CTX_PTR)Ppmd7_RemoveNode(p, 0);
    else
    {
      c1 = (PPMD7_CTX_PTR)Ppmd7_AllocUnitsRare(p, 0);
      if (!c1)
        return NULL;
    }

    c1->NumStats = 1;
    ONE_STATE(c1)->Symbol = newSym;
    ONE_STATE(c1)->Freq = newFreq;
    SetSuccessor(ONE_STATE(c1), upBranch);
    c1->Suffix = REF(c);
    SetSuccessor(ps[--numPs], REF(c1));
    c = c1;
  }
  while (numPs != 0);

  return c;
}



#define SWAP_STATES(s) \
  { CPpmd_State tmp = s[0]; s[0] = s[-1]; s[-1] = tmp; }


void Ppmd7_UpdateModel(CPpmd7 *p);
Z7_NO_INLINE
void Ppmd7_UpdateModel(CPpmd7 *p)
{
  CPpmd_Void_Ref maxSuccessor, minSuccessor;
  PPMD7_CTX_PTR c, mc;
  unsigned s0, ns;



  if (p->FoundState->Freq < MAX_FREQ / 4 && p->MinContext->Suffix != 0)
  {
    /* Update Freqs in Suffix Context */

    c = SUFFIX(p->MinContext);

    if (c->NumStats == 1)
    {
      CPpmd_State *s = ONE_STATE(c);
      if (s->Freq < 32)
        s->Freq++;
    }
    else
    {
      CPpmd_State *s = STATS(c);
      Byte sym = p->FoundState->Symbol;

      if (s->Symbol != sym)
      {
        do
        {
          // s++; if (s->Symbol == sym) break;
          s++;
        }
        while (s->Symbol != sym);

        if (s[0].Freq >= s[-1].Freq)
        {
          SWAP_STATES(s)
          s--;
        }
      }

      if (s->Freq < MAX_FREQ - 9)
      {
        s->Freq = (Byte)(s->Freq + 2);
        c->Union2.SummFreq = (UInt16)(c->Union2.SummFreq + 2);
      }
    }
  }


  if (p->OrderFall == 0)
  {
    /* MAX ORDER context */
    /* (FoundState->Successor) is RAW-Successor. */
    p->MaxContext = p->MinContext = Ppmd7_CreateSuccessors(p);
    if (!p->MinContext)
    {
      Ppmd7_RestartModel(p);
      return;
    }
    SetSuccessor(p->FoundState, REF(p->MinContext));
    return;
  }


  /* NON-MAX ORDER context */

  {
    Byte *text = p->Text;
    *text++ = p->FoundState->Symbol;
    p->Text = text;
    if (text >= p->UnitsStart)
    {
      Ppmd7_RestartModel(p);
      return;
    }
    maxSuccessor = REF(text);
  }

  minSuccessor = SUCCESSOR(p->FoundState);

  if (minSuccessor)
  {
    // there is Successor for FoundState in MinContext.
    // So the next context will be one order higher than MinContext.

    if (minSuccessor <= maxSuccessor)
    {
      // minSuccessor is RAW-Successor. So we will create real contexts records:
      PPMD7_CTX_PTR cs = Ppmd7_CreateSuccessors(p);
      if (!cs)
      {
        Ppmd7_RestartModel(p);
        return;
      }
      minSuccessor = REF(cs);
    }

    // minSuccessor now is real Context pointer that points to existing (Order+1) context

    if (--p->OrderFall == 0)
    {
      /*
      if we move to MaxOrder context, then minSuccessor will be common Succesor for both:
        MinContext that is (MaxOrder - 1)
        MaxContext that is (MaxOrder)
      so we don't need new RAW-Successor, and we can use real minSuccessor
      as succssors for both MinContext and MaxContext.
      */
      maxSuccessor = minSuccessor;

      /*
      if (MaxContext != MinContext)
      {
        there was order fall from MaxOrder and we don't need current symbol
        to transfer some RAW-Succesors to real contexts.
        So we roll back pointer in raw data for one position.
      }
      */
      p->Text -= (p->MaxContext != p->MinContext);
    }
  }
  else
  {
    /*
    FoundState has NULL-Successor here.
    And only root 0-order context can contain NULL-Successors.
    We change Successor in FoundState to RAW-Successor,
    And next context will be same 0-order root Context.
    */
    SetSuccessor(p->FoundState, maxSuccessor);
    minSuccessor = REF(p->MinContext);
  }

  mc = p->MinContext;
  c = p->MaxContext;

  p->MaxContext = p->MinContext = CTX(minSuccessor);

  if (c == mc)
    return;

  // s0 : is pure Escape Freq
  s0 = mc->Union2.SummFreq - (ns = mc->NumStats) - ((unsigned)p->FoundState->Freq - 1);

  do
  {
    unsigned ns1;
    UInt32 sum;

    if ((ns1 = c->NumStats) != 1)
    {
      if ((ns1 & 1) == 0)
      {
        /* Expand for one UNIT */
        const unsigned oldNU = ns1 >> 1;
        const unsigned i = U2I(oldNU);
        if (i != U2I((size_t)oldNU + 1))
        {
          void *ptr = Ppmd7_AllocUnits(p, i + 1);
          void *oldPtr;
          if (!ptr)
          {
            Ppmd7_RestartModel(p);
            return;
          }
          oldPtr = STATS(c);
          MEM_12_CPY(ptr, oldPtr, oldNU)
          Ppmd7_InsertNode(p, oldPtr, i);
          c->Union4.Stats = STATS_REF(ptr);
        }
      }
      sum = c->Union2.SummFreq;
      /* max increase of Escape_Freq is 3 here.
         total increase of Union2.SummFreq for all symbols is less than 256 here */
      sum += (UInt32)(unsigned)((2 * ns1 < ns) + 2 * ((unsigned)(4 * ns1 <= ns) & (sum <= 8 * ns1)));
      /* original PPMdH uses 16-bit variable for (sum) here.
         But (sum < 0x9000). So we don't truncate (sum) to 16-bit */
      // sum = (UInt16)sum;
    }
    else
    {
      // instead of One-symbol context we create 2-symbol context
      CPpmd_State *s = (CPpmd_State*)Ppmd7_AllocUnits(p, 0);
      if (!s)
      {
        Ppmd7_RestartModel(p);
        return;
      }
      {
        unsigned freq = c->Union2.State2.Freq;
        // s = *ONE_STATE(c);
        s->Symbol = c->Union2.State2.Symbol;
        s->Successor_0 = c->Union4.State4.Successor_0;
        s->Successor_1 = c->Union4.State4.Successor_1;
        // SetSuccessor(s, c->Union4.Stats);  // call it only for debug purposes to check the order of
                                              // (Successor_0 and Successor_1) in LE/BE.
        c->Union4.Stats = REF(s);
        if (freq < MAX_FREQ / 4 - 1)
          freq <<= 1;
        else
          freq = MAX_FREQ - 4;
        // (max(s->freq) == 120), when we convert from 1-symbol into 2-symbol context
        s->Freq = (Byte)freq;
        // max(InitEsc = PPMD7_kExpEscape[*]) is 25. So the max(escapeFreq) is 26 here
        sum = (UInt32)(freq + p->InitEsc + (ns > 3));
      }
    }

    {
      CPpmd_State *s = STATS(c) + ns1;
      UInt32 cf = 2 * (sum + 6) * (UInt32)p->FoundState->Freq;
      UInt32 sf = (UInt32)s0 + sum;
      s->Symbol = p->FoundState->Symbol;
      c->NumStats = (UInt16)(ns1 + 1);
      SetSuccessor(s, maxSuccessor);

      if (cf < 6 * sf)
      {
        cf = (UInt32)1 + (cf > sf) + (cf >= 4 * sf);
        sum += 3;
        /* It can add (0, 1, 2) to Escape_Freq */
      }
      else
      {
        cf = (UInt32)4 + (cf >= 9 * sf) + (cf >= 12 * sf) + (cf >= 15 * sf);
        sum += cf;
      }

      c->Union2.SummFreq = (UInt16)sum;
      s->Freq = (Byte)cf;
    }
    c = SUFFIX(c);
  }
  while (c != mc);
}



Z7_NO_INLINE
static void Ppmd7_Rescale(CPpmd7 *p)
{
  unsigned i, adder, sumFreq, escFreq;
  CPpmd_State *stats = STATS(p->MinContext);
  CPpmd_State *s = p->FoundState;

  /* Sort the list by Freq */
  if (s != stats)
  {
    CPpmd_State tmp = *s;
    do
      s[0] = s[-1];
    while (--s != stats);
    *s = tmp;
  }

  sumFreq = s->Freq;
  escFreq = p->MinContext->Union2.SummFreq - sumFreq;

  /*
  if (p->OrderFall == 0), adder = 0 : it's     allowed to remove symbol from     MAX Order context
  if (p->OrderFall != 0), adder = 1 : it's NOT allowed to remove symbol from NON-MAX Order context
  */

  adder = (p->OrderFall != 0);

  #ifdef PPMD7_ORDER_0_SUPPPORT
  adder |= (p->MaxOrder == 0); // we don't remove symbols from order-0 context
  #endif

  sumFreq = (sumFreq + 4 + adder) >> 1;
  i = (unsigned)p->MinContext->NumStats - 1;
  s->Freq = (Byte)sumFreq;

  do
  {
    unsigned freq = (++s)->Freq;
    escFreq -= freq;
    freq = (freq + adder) >> 1;
    sumFreq += freq;
    s->Freq = (Byte)freq;
    if (freq > s[-1].Freq)
    {
      CPpmd_State tmp = *s;
      CPpmd_State *s1 = s;
      do
      {
        s1[0] = s1[-1];
      }
      while (--s1 != stats && freq > s1[-1].Freq);
      *s1 = tmp;
    }
  }
  while (--i);

  if (s->Freq == 0)
  {
    /* Remove all items with Freq == 0 */
    CPpmd7_Context *mc;
    unsigned numStats, numStatsNew, n0, n1;

    i = 0; do { i++; } while ((--s)->Freq == 0);

    /* We increase (escFreq) for the number of removed symbols.
       So we will have (0.5) increase for Escape_Freq in avarage per
       removed symbol after Escape_Freq halving */
    escFreq += i;
    mc = p->MinContext;
    numStats = mc->NumStats;
    numStatsNew = numStats - i;
    mc->NumStats = (UInt16)(numStatsNew);
    n0 = (numStats + 1) >> 1;

    if (numStatsNew == 1)
    {
      /* Create Single-Symbol context */
      unsigned freq = stats->Freq;

      do
      {
        escFreq >>= 1;
        freq = (freq + 1) >> 1;
      }
      while (escFreq > 1);

      s = ONE_STATE(mc);
      *s = *stats;
      s->Freq = (Byte)freq; // (freq <= 260 / 4)
      p->FoundState = s;
      Ppmd7_InsertNode(p, stats, U2I(n0));
      return;
    }

    n1 = (numStatsNew + 1) >> 1;
    if (n0 != n1)
    {
      // p->MinContext->Union4.Stats = STATS_REF(ShrinkUnits(p, stats, n0, n1));
      unsigned i0 = U2I(n0);
      unsigned i1 = U2I(n1);
      if (i0 != i1)
      {
        if (p->FreeList[i1] != 0)
        {
          void *ptr = Ppmd7_RemoveNode(p, i1);
          p->MinContext->Union4.Stats = STATS_REF(ptr);
          MEM_12_CPY(ptr, (const void *)stats, n1)
          Ppmd7_InsertNode(p, stats, i0);
        }
        else
          Ppmd7_SplitBlock(p, stats, i0, i1);
      }
    }
  }
  {
    CPpmd7_Context *mc = p->MinContext;
    mc->Union2.SummFreq = (UInt16)(sumFreq + escFreq - (escFreq >> 1));
    // Escape_Freq halving here
    p->FoundState = STATS(mc);
  }
}


CPpmd_See *Ppmd7_MakeEscFreq(CPpmd7 *p, unsigned numMasked, UInt32 *escFreq)
{
  CPpmd_See *see;
  const CPpmd7_Context *mc = p->MinContext;
  unsigned numStats = mc->NumStats;
  if (numStats != 256)
  {
    unsigned nonMasked = numStats - numMasked;
    see = p->See[(unsigned)p->NS2Indx[(size_t)nonMasked - 1]]
        + (nonMasked < (unsigned)SUFFIX(mc)->NumStats - numStats)
        + 2 * (unsigned)(mc->Union2.SummFreq < 11 * numStats)
        + 4 * (unsigned)(numMasked > nonMasked) +
        p->HiBitsFlag;
    {
      // if (see->Summ) field is larger than 16-bit, we need only low 16 bits of Summ
      const unsigned summ = (UInt16)see->Summ; // & 0xFFFF
      const unsigned r = (summ >> see->Shift);
      see->Summ = (UInt16)(summ - r);
      *escFreq = (UInt32)(r + (r == 0));
    }
  }
  else
  {
    see = &p->DummySee;
    *escFreq = 1;
  }
  return see;
}


static void Ppmd7_NextContext(CPpmd7 *p)
{
  PPMD7_CTX_PTR c = CTX(SUCCESSOR(p->FoundState));
  if (p->OrderFall == 0 && (const Byte *)c > p->Text)
    p->MaxContext = p->MinContext = c;
  else
    Ppmd7_UpdateModel(p);
}


void Ppmd7_Update1(CPpmd7 *p)
{
  CPpmd_State *s = p->FoundState;
  unsigned freq = s->Freq;
  freq += 4;
  p->MinContext->Union2.SummFreq = (UInt16)(p->MinContext->Union2.SummFreq + 4);
  s->Freq = (Byte)freq;
  if (freq > s[-1].Freq)
  {
    SWAP_STATES(s)
    p->FoundState = --s;
    if (freq > MAX_FREQ)
      Ppmd7_Rescale(p);
  }
  Ppmd7_NextContext(p);
}


void Ppmd7_Update1_0(CPpmd7 *p)
{
  CPpmd_State *s = p->FoundState;
  CPpmd7_Context *mc = p->MinContext;
  unsigned freq = s->Freq;
  const unsigned summFreq = mc->Union2.SummFreq;
  p->PrevSuccess = (2 * freq > summFreq);
  p->RunLength += (Int32)p->PrevSuccess;
  mc->Union2.SummFreq = (UInt16)(summFreq + 4);
  freq += 4;
  s->Freq = (Byte)freq;
  if (freq > MAX_FREQ)
    Ppmd7_Rescale(p);
  Ppmd7_NextContext(p);
}


/*
void Ppmd7_UpdateBin(CPpmd7 *p)
{
  unsigned freq = p->FoundState->Freq;
  p->FoundState->Freq = (Byte)(freq + (freq < 128));
  p->PrevSuccess = 1;
  p->RunLength++;
  Ppmd7_NextContext(p);
}
*/

void Ppmd7_Update2(CPpmd7 *p)
{
  CPpmd_State *s = p->FoundState;
  unsigned freq = s->Freq;
  freq += 4;
  p->RunLength = p->InitRL;
  p->MinContext->Union2.SummFreq = (UInt16)(p->MinContext->Union2.SummFreq + 4);
  s->Freq = (Byte)freq;
  if (freq > MAX_FREQ)
    Ppmd7_Rescale(p);
  Ppmd7_UpdateModel(p);
}



/*
PPMd Memory Map:
{
  [ 0 ]           contains subset of original raw text, that is required to create context
                  records, Some symbols are not written, when max order context was reached
  [ Text ]        free area
  [ UnitsStart ]  CPpmd_State vectors and CPpmd7_Context records
  [ LoUnit ]      free  area for CPpmd_State and CPpmd7_Context items
[ HiUnit ]      CPpmd7_Context records
  [ Size ]        end of array
}

These addresses don't cross at any time.
And the following condtions is true for addresses:
  (0  <= Text < UnitsStart <= LoUnit <= HiUnit <= Size)

Raw text is BYTE--aligned.
the data in block [ UnitsStart ... Size ] contains 12-bytes aligned UNITs.

Last UNIT of array at offset (Size - 12) is root order-0 CPpmd7_Context record.
The code can free UNITs memory blocks that were allocated to store CPpmd_State vectors.
The code doesn't free UNITs allocated for CPpmd7_Context records.

The code calls Ppmd7_RestartModel(), when there is no free memory for allocation.
And Ppmd7_RestartModel() changes the state to orignal start state, with full free block.


The code allocates UNITs with the following order:

Allocation of 1 UNIT for Context record
  - from free space (HiUnit) down to (LoUnit)
  - from FreeList[0]
  - Ppmd7_AllocUnitsRare()

Ppmd7_AllocUnits() for CPpmd_State vectors:
  - from FreeList[i]
  - from free space (LoUnit) up to (HiUnit)
  - Ppmd7_AllocUnitsRare()

Ppmd7_AllocUnitsRare()
  - if (GlueCount == 0)
       {  Glue lists, GlueCount = 255, allocate from FreeList[i]] }
  - loop for all higher sized FreeList[...] lists
  - from (UnitsStart - Text), GlueCount--
  - ERROR


Each Record with Context contains the CPpmd_State vector, where each
CPpmd_State contains the link to Successor.
There are 3 types of Successor:
  1) NULL-Successor   - NULL pointer. NULL-Successor links can be stored
                        only in 0-order Root Context Record.
                        We use 0 value as NULL-Successor
  2) RAW-Successor    - the link to position in raw text,
                        that "RAW-Successor" is being created after first
                        occurrence of new symbol for some existing context record.
                        (RAW-Successor > 0).
  3) RECORD-Successor - the link to CPpmd7_Context record of (Order+1),
                        that record is being created when we go via RAW-Successor again.

For any successors at any time: the following condtions are true for Successor links:
(NULL-Successor < RAW-Successor < UnitsStart <= RECORD-Successor)


---------- Symbol Frequency, SummFreq and Range in Range_Coder ----------

CPpmd7_Context::SummFreq = Sum(Stats[].Freq) + Escape_Freq

The PPMd code tries to fulfill the condition:
  (SummFreq <= (256 * 128 = RC::kBot))

We have (Sum(Stats[].Freq) <= 256 * 124), because of (MAX_FREQ = 124)
So (4 = 128 - 124) is average reserve for Escape_Freq for each symbol.
If (CPpmd_State::Freq) is not aligned for 4, the reserve can be 5, 6 or 7.
SummFreq and Escape_Freq can be changed in Ppmd7_Rescale() and *Update*() functions.
Ppmd7_Rescale() can remove symbols only from max-order contexts. So Escape_Freq can increase after multiple calls of Ppmd7_Rescale() for
max-order context.

When the PPMd code still break (Total <= RC::Range) condition in range coder,
we have two ways to resolve that problem:
  1) we can report error, if we want to keep compatibility with original PPMd code that has no fix for such cases.
  2) we can reduce (Total) value to (RC::Range) by reducing (Escape_Freq) part of (Total) value.
*/

#undef MAX_FREQ
#undef UNIT_SIZE
#undef U2B
#undef U2I
#undef I2U
#undef I2U_UInt16
#undef REF
#undef STATS_REF
#undef CTX
#undef STATS
#undef ONE_STATE
#undef SUFFIX
#undef NODE
#undef EMPTY_NODE
#undef MEM_12_CPY
#undef SUCCESSOR
#undef SWAP_STATES