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From: routley@tle.enet.dec.com
Newsgroups: comp.os.msdos.programmer
Subject: TC++ bugs reported to Borland
Message-ID: <16797@shlump.nac.dec.com>
Date: 29 Oct 90 22:20:42 GMT
Sender: newsdaemon@shlump.nac.dec.com
Reply-To: routley@tle.enet.dec.com ()
Organization: Digital Equipment Corporation
Lines: 155

I have submitted the following TC++ bug report to Borland.

Kevin Routley - Digital Equipment Corporation
routley@tle.enet.dec.com

          Product: Turbo C++
          Version: 1.00
          OS: MS-DOS V3.2


          1. Bitfield Operation Performance

             Bitfield operations are not optimal. See Example 1
             for an example program.

             Testing the first bit of a multi-bit bitfield struc-
             ture is done in 20 (8086) cycles with the TEST
             instruction:

                  TEST    WORD PTR [BP-06], 0001

             The third bit in a multi-bit bitfield structure is
             testing by performing a pair of shift instructions,
             requiring 25 cycles:

                  MOV    AX, WORD PTR [BP-06]
                  SHR    AX, 1
                  SHR    AX, 1
                  TEST   AX, 0001

             Larger bitfield structures use the multiple shift
             instruction to test higher bits. For example, the
             eighth bit requires seven shifts and 61 cycles to
             test:

                  MOV    AX, WORD PTR [BP-06]
                  MOV    CL, 7
                  SHR    AX, CL
                  TEST   AX, 0001

             This poor optimization places severe penalties on
             those programs that might choose to use bitfields
             to store flags instead of char objects. As far as
             space is concerned, it is more efficient to use a
             bitfield structure for three or more boolean flags
             rather than chars.

             The bitwise & operator illustrates that all three
             tests above could have been performed with individ-
             ual TEST instructions (a total of 63 cycles compared
             to the 106 cycles required by the above tests):

                  TEST    WORD PTR [BP-06], 0001
                  TEST    WORD PTR [BP-06], 0004
                  TEST    WORD PTR [BP-06], 0080

             In fact, a series of similar (& or |) operations on
             bitfield structure elements could be optimized to a
             single TEST instruction.

          Example 1:  Example Bitfield Program
          _______________________________________________________

          #include <stdio.h>
          main()
              {
              struct foo
                  {
                  unsigned flag1 : 1;
                  unsigned flag2 : 1;
                  unsigned flag3 : 1;
                  unsigned flag4 : 1;
                  unsigned flag5 : 1;
                  unsigned flag6 : 1;
                  unsigned flag7 : 1;
                  unsigned flag8 : 1;
                  } flags;

              char lflag1 = 0;
              char lflag2 = 1;
              char lflag3 = 0;
              char lflag4 = 1;

              flags.flag1 = flags.flag8 = 1;

              if ( flags.flag1 &&
                   flags.flag8 &&
                   lflag2      &&
                   lflag4        )
                  printf("True\n");
              else
                  printf("False\n");
          ____}__________________________________________________

          2. Macro Expansion Limit

             The limitation of 4096 characters for a macro ex-
             pansion is too small for non-toy programs. This can
             prevent Turbo C++ from being used as a development
             environment for large programs. Ideally a macro
             expansion should only be limited by the compiling
             machine's memory (if that, using memory swapping).

             As an example, multiple data structures can be
             easily and conveniently initialized from a single
             instance of the entered information (illustrated
             in Example 2. If table_data contains more than a
             few lines with more than a couple of items, and the
             author uses spaces to insure readibility, you can
             easily exceed the 4096 character limit.

          Example 2:  Struct Init. from a Single Set of Data
          _______________________________________________________

          /* setup the data to init all the structures with
          */
          #define table_data \
             X( "text1",    0,    CONST1, 1, 1, 0,     struct1, 1 )\
             X( "text1234", 0, CONST1234, 1, 1, 0,     struct2, 1 )\
              . . .
             X( "text99",   0,   CONST99, 0, 0, 0, structure99, 0 )

          /* setup the macro to init table1. Only some of the fields
             are used.
          */
          #define X (string, foo, bar, fum, foobar, dataptr, flag )\
              { foo, bar, fum, flag }

          /* table1 is an array of structs, each with four int fields
          */
          table1[MAX_TABLE] = { table_data };

          #undef X

          /* setup a different macro to init table2.  Different fields
             are used this time.
          */
          #define X (string, foo, bar, fum, foobar, dataptr, flag )\
              { flag, string }

          table2[MAX_TABLE] = { table_data };
          #undef_X_______________________________________________

          3. TC.EXE Display Customization

             I am unable to customize the colors of the inte-
             grated environment so that they display reasonably
             on my monochrome VGA monitor.

             TCINST has an option "Mode for Display". No matter
             which option I select (e.g. Black and White, or
             Monochrome) to customize TC.EXE to have, I always
             get the same default color display mode when I
             invoke TC.EXE. The default mode is very difficult to
             read on my monochrome display.