SQLite

      int i;

      if( !zDetail ) continue;
      nDetail = STRLEN(zDetail);

      for(i=0; i<nDetail; i++){
        const char *zIdx = 0;
        if( i+13<nDetail && memcmp(&zDetail[i], " USING INDEX ", 13)==0 ){
          zIdx = &zDetail[i+13];
        }else if( i+22<nDetail 
            && memcmp(&zDetail[i], " USING COVERING INDEX ", 22)==0 
        ){
          zIdx = &zDetail[i+22];
        }
        if( zIdx ){
          const char *zSql;
          int nIdx = 0;
          while( zIdx[nIdx]!='\0' && (zIdx[nIdx]!=' ' || zIdx[nIdx+1]!='(') ){
            nIdx++;

2  COMPILATION AND USAGE

  The easiest way to compile and use the ICU extension is to build
  and use it as a dynamically loadable SQLite extension. To do this
  using gcc on *nix:

    gcc -fPIC -shared icu.c `pkg-config --libs --cflags icu-uc icu-io` \
        -o libSqliteIcu.so

  You may need to add "-I" flags so that gcc can find sqlite3ext.h
  and sqlite3.h. The resulting shared lib, libSqliteIcu.so, may be
  loaded into sqlite in the same way as any other dynamically loadable
  extension.

** This routine is called when the extension is loaded.
** Register the new VFS.
*/
int sqlite3MemdbInit(void){
  sqlite3_vfs *pLower = sqlite3_vfs_find(0);
  int sz = pLower->szOsFile;
  memdb_vfs.pAppData = pLower;


  /* The following conditional can only be true when compiled for
  ** Windows x86 and SQLITE_MAX_MMAP_SIZE=0.  We always leave
  ** it in, to be safe, but it is marked as NO_TEST since there
  ** is no way to reach it under most builds. */
  if( sz<sizeof(MemFile) ) sz = sizeof(MemFile); /*NO_TEST*/
  memdb_vfs.szOsFile = sz;
  return sqlite3_vfs_register(&memdb_vfs, 0);
}
#endif /* SQLITE_ENABLE_DESERIALIZE */

  sqlite3_free(zTmpname);
  pFile->pMethod = pAppData ? pAppData->pMethod : &winIoMethod;
  pFile->pVfs = pVfs;
  pFile->h = h;
  if( isReadonly ){
    pFile->ctrlFlags |= WINFILE_RDONLY;
  }
  if( (flags & SQLITE_OPEN_MAIN_DB)
   && sqlite3_uri_boolean(zName, "psow", SQLITE_POWERSAFE_OVERWRITE) 
  ){
    pFile->ctrlFlags |= WINFILE_PSOW;
  }
  pFile->lastErrno = NO_ERROR;
  pFile->zPath = zName;
#if SQLITE_MAX_MMAP_SIZE>0
  pFile->hMap = NULL;
  pFile->pMapRegion = 0;

    assert( desiredEnc==SQLITE_UTF8 );
    if( pMem->enc==SQLITE_UTF16LE ){
      /* UTF-16 Little-endian -> UTF-8 */
      while( zIn<zTerm ){
        c = *(zIn++);
        c += (*(zIn++))<<8;
        if( c>=0xd800 && c<0xe000 ){
#ifdef SQLITE_REPLACE_INVALID_UTF
          if( c>=0xdc00 || zIn>=zTerm ){
            c = 0xfffd;
          }else{
            int c2 = *(zIn++);
            c2 += (*(zIn++))<<8;
            if( c2<0xdc00 || c2>=0xe000 ){
              zIn -= 2;
              c = 0xfffd;
            }else{
              c = ((c&0x3ff)<<10) + (c2&0x3ff) + 0x10000;
            }
          }
#else
          if( zIn<zTerm ){
            int c2 = (*zIn++);
            c2 += ((*zIn++)<<8);
            c = (c2&0x03FF) + ((c&0x003F)<<10) + (((c&0x03C0)+0x0040)<<10);
          }
#endif
        }
        WRITE_UTF8(z, c);
      }
    }else{
      /* UTF-16 Big-endian -> UTF-8 */
      while( zIn<zTerm ){
        c = (*(zIn++))<<8;
        c += *(zIn++);
        if( c>=0xd800 && c<0xe000 ){
#ifdef SQLITE_REPLACE_INVALID_UTF
          if( c>=0xdc00 || zIn>=zTerm ){
            c = 0xfffd;
          }else{
            int c2 = (*(zIn++))<<8;
            c2 += *(zIn++);
            if( c2<0xdc00 || c2>=0xe000 ){
              zIn -= 2;
              c = 0xfffd;
            }else{
              c = ((c&0x3ff)<<10) + (c2&0x3ff) + 0x10000;
            }
          }
#else
          if( zIn<zTerm ){
            int c2 = ((*zIn++)<<8);
            c2 += (*zIn++);
            c = (c2&0x03FF) + ((c&0x003F)<<10) + (((c&0x03C0)+0x0040)<<10);
          }
#endif
        }
        WRITE_UTF8(z, c);
      }
    }
    pMem->n = (int)(z - zOut);
  }
  *z = 0;

    }while( aData<aEnd );
  }

  aOut[0] = s1;
  aOut[1] = s2;
}

/*
** If there is the possibility of concurrent access to the SHM file
** from multiple threads and/or processes, then do a memory barrier.
*/
static void walShmBarrier(Wal *pWal){
  if( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE ){
    sqlite3OsShmBarrier(pWal->pDbFd);
  }
}

/*
** Add the SQLITE_NO_TSAN as part of the return-type of a function
** definition as a hint that the function contains constructs that
** might give false-positive TSAN warnings.
**
** See tag-20200519-1.
*/
#if defined(__clang__) && !defined(SQLITE_NO_TSAN)
# define SQLITE_NO_TSAN __attribute__((no_sanitize_thread))
#else
# define SQLITE_NO_TSAN
#endif

/*
** Write the header information in pWal->hdr into the wal-index.
**
** The checksum on pWal->hdr is updated before it is written.
*/
static SQLITE_NO_TSAN void walIndexWriteHdr(Wal *pWal){
  volatile WalIndexHdr *aHdr = walIndexHdr(pWal);
  const int nCksum = offsetof(WalIndexHdr, aCksum);

  assert( pWal->writeLock );
  pWal->hdr.isInit = 1;
  pWal->hdr.iVersion = WALINDEX_MAX_VERSION;
  walChecksumBytes(1, (u8*)&pWal->hdr, nCksum, 0, pWal->hdr.aCksum);
  /* Possible TSAN false-positive.  See tag-20200519-1 */
  memcpy((void*)&aHdr[1], (const void*)&pWal->hdr, sizeof(WalIndexHdr));
  walShmBarrier(pWal);
  memcpy((void*)&aHdr[0], (const void*)&pWal->hdr, sizeof(WalIndexHdr));
}

/*
** This function encodes a single frame header and writes it to a buffer

    ** safe to write into the database.  Frames beyond mxSafeFrame might
    ** overwrite database pages that are in use by active readers and thus
    ** cannot be backfilled from the WAL.
    */
    mxSafeFrame = pWal->hdr.mxFrame;
    mxPage = pWal->hdr.nPage;
    for(i=1; i<WAL_NREADER; i++){




















      u32 y = AtomicLoad(pInfo->aReadMark+i);
      if( mxSafeFrame>y ){
        assert( y<=pWal->hdr.mxFrame );
        rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(i), 1);
        if( rc==SQLITE_OK ){
          u32 iMark = (i==1 ? mxSafeFrame : READMARK_NOT_USED);
          AtomicStore(pInfo->aReadMark+i, iMark);
          walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
        }else if( rc==SQLITE_BUSY ){
          mxSafeFrame = y;
          xBusy = 0;
        }else{
          goto walcheckpoint_out;
        }
      }
    }

    /* Allocate the iterator */
    if( pInfo->nBackfill<mxSafeFrame ){
      rc = walIteratorInit(pWal, pInfo->nBackfill, &pIter);
      assert( rc==SQLITE_OK || pIter==0 );
    }

    if( pIter
     && (rc = walBusyLock(pWal,xBusy,pBusyArg,WAL_READ_LOCK(0),1))==SQLITE_OK
    ){
      u32 nBackfill = pInfo->nBackfill;

      pInfo->nBackfillAttempted = mxSafeFrame;

      /* Sync the WAL to disk */
      rc = sqlite3OsSync(pWal->pWalFd, CKPT_SYNC_FLAGS(sync_flags));

** If and only if the read is consistent and the header is different from
** pWal->hdr, then pWal->hdr is updated to the content of the new header
** and *pChanged is set to 1.
**
** If the checksum cannot be verified return non-zero. If the header
** is read successfully and the checksum verified, return zero.
*/
static SQLITE_NO_TSAN int walIndexTryHdr(Wal *pWal, int *pChanged){
  u32 aCksum[2];                  /* Checksum on the header content */
  WalIndexHdr h1, h2;             /* Two copies of the header content */
  WalIndexHdr volatile *aHdr;     /* Header in shared memory */

  /* The first page of the wal-index must be mapped at this point. */
  assert( pWal->nWiData>0 && pWal->apWiData[0] );

  /* Read the header. This might happen concurrently with a write to the
  ** same area of shared memory on a different CPU in a SMP,
  ** meaning it is possible that an inconsistent snapshot is read
  ** from the file. If this happens, return non-zero.
  **
  ** tag-20200519-1:
  ** There are two copies of the header at the beginning of the wal-index.
  ** When reading, read [0] first then [1].  Writes are in the reverse order.
  ** Memory barriers are used to prevent the compiler or the hardware from
  ** reordering the reads and writes.  TSAN and similar tools can sometimes
  ** give false-positive warnings about these accesses because the tools do not
  ** account for the double-read and the memory barrier. The use of mutexes
  ** here would be problematic as the memory being accessed is potentially
  ** shared among multiple processes and not all mutex implementions work
  ** reliably in that environment.
  */
  aHdr = walIndexHdr(pWal);
  memcpy(&h1, (void *)&aHdr[0], sizeof(h1)); /* Possible TSAN false-positive */
  walShmBarrier(pWal);
  memcpy(&h2, (void *)&aHdr[1], sizeof(h2));

  if( memcmp(&h1, &h2, sizeof(h1))!=0 ){
    return 1;   /* Dirty read */
  }  
  if( h1.isInit==0 ){

  */
  iMinHash = walFramePage(pWal->minFrame);
  for(iHash=walFramePage(iLast); iHash>=iMinHash; iHash--){
    WalHashLoc sLoc;              /* Hash table location */
    int iKey;                     /* Hash slot index */
    int nCollide;                 /* Number of hash collisions remaining */
    int rc;                       /* Error code */
    u32 iH;

    rc = walHashGet(pWal, iHash, &sLoc);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    nCollide = HASHTABLE_NSLOT;
    iKey = walHash(pgno);
    while( (iH = AtomicLoad(&sLoc.aHash[iKey]))!=0 ){
      u32 iFrame = iH + sLoc.iZero;
      if( iFrame<=iLast && iFrame>=pWal->minFrame && sLoc.aPgno[iH]==pgno ){
        assert( iFrame>iRead || CORRUPT_DB );
        iRead = iFrame;
      }
      if( (nCollide--)==0 ){
        return SQLITE_CORRUPT_BKPT;
      }
      iKey = walNextHash(iKey);
    }
    if( iRead ) break;
  }

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
  /* If expensive assert() statements are available, do a linear search
  ** of the wal-index file content. Make sure the results agree with the

  sqlite3 db :memory:
  db eval {
    PRAGMA encoding=UTF8;
    CREATE TABLE t1(x);
    INSERT INTO t1 VALUES(hex_to_utf16be('D800'));
    SELECT hex(x) FROM t1;
  }
} {EDA080}
do_test tkt-3fe89-1.2 {
  db eval {
    DELETE FROM t1;
    INSERT INTO t1 VALUES(hex_to_utf16le('00D8'));
    SELECT hex(x) FROM t1;
  }
} {EDA080}
do_test tkt-3fe89-1.3 {
  db eval {
    DELETE FROM t1;
    INSERT INTO t1 VALUES(hex_to_utf16be('DFFF'));
    SELECT hex(x) FROM t1;
  }
} {EDBFBF}
do_test tkt-3fe89-1.4 {
  db eval {
    DELETE FROM t1;
    INSERT INTO t1 VALUES(hex_to_utf16le('FFDF'));
    SELECT hex(x) FROM t1;
  }
} {EDBFBF}


finish_test