text: /* 7zCrc.c -- CRC32 init
  2017-06-06 : Igor Pavlov : Public domain */
  
  #include "Precomp.h"
  
  #include "7zCrc.h"
  #include "CpuArch.h"
  
  #define kCrcPoly 0xEDB88320
  
  #ifdef MY_CPU_LE
    #define CRC_NUM_TABLES 8
  #else
    #define CRC_NUM_TABLES 9
  
    #define CRC_UINT32_SWAP(v) ((v >> 24) | ((v >> 8) & 0xFF00) | ((v << 8) & 0xFF0000) | (v << 24))
  
    UInt32 MY_FAST_CALL CrcUpdateT1_BeT4(UInt32 v, const void *data, size_t size, const UInt32 *table);
    UInt32 MY_FAST_CALL CrcUpdateT1_BeT8(UInt32 v, const void *data, size_t size, const UInt32 *table);
  #endif
  
  #ifndef MY_CPU_BE
    UInt32 MY_FAST_CALL CrcUpdateT4(UInt32 v, const void *data, size_t size, const UInt32 *table);
    UInt32 MY_FAST_CALL CrcUpdateT8(UInt32 v, const void *data, size_t size, const UInt32 *table);
  #endif
  
  typedef UInt32 (MY_FAST_CALL *CRC_FUNC)(UInt32 v, const void *data, size_t size, const UInt32 *table);
  
  CRC_FUNC g_CrcUpdateT4;
  CRC_FUNC g_CrcUpdateT8;
  CRC_FUNC g_CrcUpdate;
  
  UInt32 g_CrcTable[256 * CRC_NUM_TABLES];
  
  UInt32 MY_FAST_CALL CrcUpdate(UInt32 v, const void *data, size_t size)
  {
    return g_CrcUpdate(v, data, size, g_CrcTable);
  }
  
  UInt32 MY_FAST_CALL CrcCalc(const void *data, size_t size)
  {
    return g_CrcUpdate(CRC_INIT_VAL, data, size, g_CrcTable) ^ CRC_INIT_VAL;
  }
  
  #define CRC_UPDATE_BYTE_2(crc, b) (table[((crc) ^ (b)) & 0xFF] ^ ((crc) >> 8))
  
  UInt32 MY_FAST_CALL CrcUpdateT1(UInt32 v, const void *data, size_t size, const UInt32 *table)
  {
    const Byte *p = (const Byte *)data;
    const Byte *pEnd = p + size;
    for (; p != pEnd; p++)
      v = CRC_UPDATE_BYTE_2(v, *p);
    return v;
  }
  
  void MY_FAST_CALL CrcGenerateTable()
  {
    UInt32 i;
    for (i = 0; i < 256; i++)
    {
      UInt32 r = i;
      unsigned j;
      for (j = 0; j < 8; j++)
        r = (r >> 1) ^ (kCrcPoly & ((UInt32)0 - (r & 1)));
      g_CrcTable[i] = r;
    }
    for (i = 256; i < 256 * CRC_NUM_TABLES; i++)
    {
      UInt32 r = g_CrcTable[(size_t)i - 256];
      g_CrcTable[i] = g_CrcTable[r & 0xFF] ^ (r >> 8);
    }
  
    #if CRC_NUM_TABLES < 4
    
    g_CrcUpdate = CrcUpdateT1;
    
    #else
   
    #ifdef MY_CPU_LE
  
      g_CrcUpdateT4 = CrcUpdateT4;
      g_CrcUpdate = CrcUpdateT4;
  
      #if CRC_NUM_TABLES >= 8
        g_CrcUpdateT8 = CrcUpdateT8;
    
        #ifdef MY_CPU_X86_OR_AMD64
        if (!CPU_Is_InOrder())
        #endif
          g_CrcUpdate = CrcUpdateT8;
      #endif
  
    #else
    {
      #ifndef MY_CPU_BE
      UInt32 k = 0x01020304;
      const Byte *p = (const Byte *)&k;
      if (p[0] == 4 && p[1] == 3)
      {
        g_CrcUpdateT4 = CrcUpdateT4;
        g_CrcUpdate = CrcUpdateT4;
        #if CRC_NUM_TABLES >= 8
        g_CrcUpdateT8 = CrcUpdateT8;
        g_CrcUpdate = CrcUpdateT8;
        #endif
      }
      else if (p[0] != 1 || p[1] != 2)
        g_CrcUpdate = CrcUpdateT1;
      else
      #endif
      {
        for (i = 256 * CRC_NUM_TABLES - 1; i >= 256; i--)
        {
          UInt32 x = g_CrcTable[(size_t)i - 256];
          g_CrcTable[i] = CRC_UINT32_SWAP(x);
        }
        g_CrcUpdateT4 = CrcUpdateT1_BeT4;
        g_CrcUpdate = CrcUpdateT1_BeT4;
        #if CRC_NUM_TABLES >= 8
        g_CrcUpdateT8 = CrcUpdateT1_BeT8;
        g_CrcUpdate = CrcUpdateT1_BeT8;
        #endif
      }
    }
    #endif
  
    #endif
  }
  