XrdOssCsiCrcUtils.hh

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#ifndef _XRDOSSCSICRCUTILS_H
#define _XRDOSSCSICRCUTILS_H
/******************************************************************************/
/*                                                                            */
/*                X r d O s s C s i C r c U t i l s . h h                     */
/*                                                                            */
/* (C) Copyright 2021 CERN.                                                   */
/*                                                                            */
/* This file is part of the XRootD software suite.                            */
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/* XRootD is free software: you can redistribute it and/or modify it under    */
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#include "XrdOuc/XrdOucCRC.hh"
#include "XrdSys/XrdSysPageSize.hh"
#include "assert.h"
 
class XrdOssCsiCrcUtils {
public:
 
   // crc32c_combine
   //
   // crc1: crc32c value of data1
   // crc2: crc32c value of data2
   // len2: length of data2
   //
   // returns crc of concatenation of data1|data2
   // note: using Calc32C: some optimisation could be made
   static uint32_t crc32c_combine(uint32_t crc1, uint32_t crc2, size_t len2)
   {
      if (len2==0)
         return crc1;
 
      assert(len2<=XrdSys::PageSize);
 
      const uint32_t c1 = XrdOucCRC::Calc32C(g_bz, len2, ~crc1);
      return ~c1^crc2;
   }
 
   // crc32c_split1
   //
   // crctot: crc32c of data1|data2
   // crc2:   crc32c of data2
   // len2:   length of data2
   //
   // returns crc of data1
   // note: crc bitshift to right, significant optimisation likely
   //       possible with intrinsics or a precomputed table
   static uint32_t crc32c_split1(uint32_t crctot, uint32_t crc2, size_t len2)
   {
      if (len2==0)
         return crctot;
 
      assert(len2<=XrdSys::PageSize);
      uint32_t crc = (crctot ^ crc2);
      for(size_t i=0;i<8*len2;i++) {
         crc = (crc<<1)^((crc&0x80000000) ? (CrcPoly << 1 | 0x1) : 0);
      }
      return crc;
   }
 
   // crc32c_split2
   //
   // crctot: crc32c of data1|data2
   // crc1:   crc32c of data1
   // len2:   length of data2
   //
   // returns crc of data2
   // note: using Calc32C: some optimisation could be made
   static uint32_t crc32c_split2(uint32_t crctot, uint32_t crc1, size_t len2)
   {
      if (len2==0)
         return 0;
 
      assert(len2<=XrdSys::PageSize);
      uint32_t c1 = XrdOucCRC::Calc32C(g_bz, len2, ~crc1);
      return ~c1^crctot;
   }
 
   // crc32c_extendwith_zero
   //
   // crc: crc32c of data
   // len: number of zero bytes to append
   //
   // returns crc of data|[0x00 x len]
   // note: using Calc32C: some optimisation could be made
   static uint32_t crc32c_extendwith_zero(uint32_t crc, size_t len)
   {
      if (len==0)
         return crc;
 
      assert(len<=XrdSys::PageSize);
      return XrdOucCRC::Calc32C(g_bz, len, crc);
   }
 
private:
 
   static const uint8_t g_bz[XrdSys::PageSize];
 
   // CRC-32C (iSCSI) polynomial in reversed bit order.
   static const uint32_t CrcPoly = 0x82F63B78;
};
 
#endif