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Overview
Comment:Tweaks to the SUBSTR() function to make it dramatically faster in the common case where the input string is large but the 2nd and 3rd arguments are small positive integers.
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SHA1: 5a474a867c5988ad5ec03719516fdd38f0da5c2c
User & Date: drh 2009-11-11 20:53:31.000
Context
2009-11-11
23:48
Remove an obsolete (and incorrect) comment from sqlite3MemCompare(). No changes to code. (check-in: c15b70b3ae user: drh tags: trunk)
20:53
Tweaks to the SUBSTR() function to make it dramatically faster in the common case where the input string is large but the 2nd and 3rd arguments are small positive integers. (check-in: 5a474a867c user: drh tags: trunk)
13:17
Allow media sector sizes as small as 32. The former minimum size was 512. (check-in: 5a32bfc17e user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/func.c.
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  assert( argc==3 || argc==2 );
  if( sqlite3_value_type(argv[1])==SQLITE_NULL
   || (argc==3 && sqlite3_value_type(argv[2])==SQLITE_NULL)
  ){
    return;
  }
  p0type = sqlite3_value_type(argv[0]);

  if( p0type==SQLITE_BLOB ){
    len = sqlite3_value_bytes(argv[0]);
    z = sqlite3_value_blob(argv[0]);
    if( z==0 ) return;
    assert( len==sqlite3_value_bytes(argv[0]) );
  }else{
    z = sqlite3_value_text(argv[0]);
    if( z==0 ) return;
    len = 0;

    for(z2=z; *z2; len++){
      SQLITE_SKIP_UTF8(z2);
    }
  }
  p1 = sqlite3_value_int(argv[1]);

  if( argc==3 ){
    p2 = sqlite3_value_int(argv[2]);
    if( p2<0 ){
      p2 = -p2;
      negP2 = 1;
    }
  }else{








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  assert( argc==3 || argc==2 );
  if( sqlite3_value_type(argv[1])==SQLITE_NULL
   || (argc==3 && sqlite3_value_type(argv[2])==SQLITE_NULL)
  ){
    return;
  }
  p0type = sqlite3_value_type(argv[0]);
  p1 = sqlite3_value_int(argv[1]);
  if( p0type==SQLITE_BLOB ){
    len = sqlite3_value_bytes(argv[0]);
    z = sqlite3_value_blob(argv[0]);
    if( z==0 ) return;
    assert( len==sqlite3_value_bytes(argv[0]) );
  }else{
    z = sqlite3_value_text(argv[0]);
    if( z==0 ) return;
    len = 0;
    if( p1<0 ){
      for(z2=z; *z2; len++){
        SQLITE_SKIP_UTF8(z2);
      }
    }

  }
  if( argc==3 ){
    p2 = sqlite3_value_int(argv[2]);
    if( p2<0 ){
      p2 = -p2;
      negP2 = 1;
    }
  }else{
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    p1 -= p2;
    if( p1<0 ){
      p2 += p1;
      p1 = 0;
    }
  }
  assert( p1>=0 && p2>=0 );
  if( p1+p2>len ){
    p2 = len-p1;
    if( p2<0 ) p2 = 0;
  }
  if( p0type!=SQLITE_BLOB ){
    while( *z && p1 ){
      SQLITE_SKIP_UTF8(z);
      p1--;
    }
    for(z2=z; *z2 && p2; p2--){
      SQLITE_SKIP_UTF8(z2);
    }
    sqlite3_result_text(context, (char*)z, (int)(z2-z), SQLITE_TRANSIENT);
  }else{




    sqlite3_result_blob(context, (char*)&z[p1], (int)p2, SQLITE_TRANSIENT);
  }
}

/*
** Implementation of the round() function
*/








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    p1 -= p2;
    if( p1<0 ){
      p2 += p1;
      p1 = 0;
    }
  }
  assert( p1>=0 && p2>=0 );




  if( p0type!=SQLITE_BLOB ){
    while( *z && p1 ){
      SQLITE_SKIP_UTF8(z);
      p1--;
    }
    for(z2=z; *z2 && p2; p2--){
      SQLITE_SKIP_UTF8(z2);
    }
    sqlite3_result_text(context, (char*)z, (int)(z2-z), SQLITE_TRANSIENT);
  }else{
    if( p1+p2>len ){
      p2 = len-p1;
      if( p2<0 ) p2 = 0;
    }
    sqlite3_result_blob(context, (char*)&z[p1], (int)p2, SQLITE_TRANSIENT);
  }
}

/*
** Implementation of the round() function
*/
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