Optimiz2.Txt

        This text file is the second part of a guide for use by QB/QBASIC
programmers to help optimize the program code for greater efficiency.  If
you have any questions, contact VirtuaSoft at gump@gnt.net.  Address to
Danny.
        (Note: This is not for the beginning programmer.  A strong
        background in QB/QBASIC programming is highly recommended.)

        2. Poke and Peek
                a. Never Use PSET and POINT
                b. Integers vs. LONG Integers
                c. Memory Segments

2. Poke and Peek

        a. Never Use PSET        
                The QB/QBASIC PSET statement is very slow.  It is this way
        because it needs to be generic so that it can work in every graphics
        screen mode.  But POKE is more specific, yet broad.  The memory
        segment to address is simply given, and a direct memory write can
        take place.  POINT is equally as slow as PSET.  PEEK should be used
        in place of POINT whenever possible.
                I will give you a hint on where to and not to use POKE and
        PEEK so that you don't confuse yourself as I did at first.  You
        should still use PSET and POINT in any graphics screen below 13H.  I
        advise this because memory is arranged in difficult to decipher ways
        in these screen modes.  Some are four bits per pixel.  Others are two
        or one.  Some divide the memory within screen pages.  Yet others use
        more than 64k requiring bank-switching (very messy if you don't know
        what you are doing).
                Screen 13H and the text screens have one byte per pixel,
        character, or character color.  This makes it very easy to address
        memory for these modes.  (Memory addressing will further be covered
        in 2c of the lesson.)

        b. Integers vs. LONG-Integers
                If you are already trying to use screen 13h (320*200*256) by
        POKEing colors, you may notice that below around the center of the
        screen, an INTEGER variable will overflow when a value > 32767 is
        POKEd.  Thus you would think that a LONG-INTEGER should be used...
        nope, it's not needed.
                For those of you who have started programming in assembly,
        you may notice that the 16-bit integers have no negative values, so
        they can go beyond BASIC's 32767 all the way to 65535.  Actually,
        this is only partially true...assembly's 16-bit numbers do have
        negatives.  -5=-5+65536=65531 (modular arithmetic)!  A negative in
        assembly is the same as that number plus 2^(# bits).
                This can be used to POKE the bottom half of the screen in
        13H.  To POKE 32768, simply take 32768-65536=-32768, and you would
        say it like this: POKE -32768, color.

        c. Memory Segments
                The foloowing are memory segments and offsets that are
        important for programming:

                                Segment                 Offset
        Graphics                &HA000                  0
        Text                    &HB800                  0
        ASCII characters        &HFFA6                  14

                The segments can be achieved by: DEF SEG=[Segment #] and
        the offsets are used whole peeking: PEEK ([Byte]+[Offset]).

               ... This concludes the lesson ...