Contributor: ALTON PRILLAMAN
{
ALTON PRILLAMAN
HOWEVER, now would be a good time to learn about "Bitwise Operators"
to accomplish your goal With minimal memory requirements. I'll start With
the basics (no offense intended). You may have heard, or remember from a
Programming class that a Byte is made up of 8 bits. When looking at a Byte
in binary, each bit holds a value of 0 or 1 that when put together in
their respective places will add up to make the number. Here's an
example of a Byte:
B I N A R Y
T A B L E
=========================================================================
Power | 7 6 5 4 3 2 1 0 | of 2
------+---------------------------------+-----
Bit # | 8 7 6 5 4 3 2 1 |
------+---------------------------------+-----
Value | 128 64 32 16 8 4 2 1 | HEX
------+---------------------------------+-----
0 | 0 0 0 0 0 0 0 0 | 00ドル
1 | 0 0 0 0 0 0 0 1 | 01ドル
* 2 | 0 0 0 0 0 0 1 0 | 02ドル
3 | 0 0 0 0 0 0 1 1 | 03ドル
* 4 | 0 0 0 0 0 1 0 0 | 04ドル
5 | 0 0 0 0 0 1 0 1 | 05ドル
6 | 0 0 0 0 0 1 1 0 | 06ドル
7 | 0 0 0 0 0 1 1 1 | 07ドル
* 8 | 0 0 0 0 1 0 0 0 | 08ドル
9 | 0 0 0 0 1 0 0 1 | 09ドル
10 | 0 0 0 0 1 0 1 0 | 0ドルA
11 | 0 0 0 0 1 0 1 1 | 0ドルB
12 | 0 0 0 0 1 1 0 0 | 0ドルC
13 | 0 0 0 0 1 1 0 1 | 0ドルD
14 | 0 0 0 0 1 1 1 0 | 0ドルE
15 | 0 0 0 0 1 1 1 1 | 0ドルF
* 16 | 0 0 0 1 0 0 0 0 | 10ドル
| |
* 32 | 0 0 1 0 0 0 0 0 | 20ドル
* 64 | 0 1 0 0 0 0 0 0 | 40ドル
* 128 | 1 0 0 0 0 0 0 0 | 80ドル
| |
255 | 1 1 1 1 1 1 1 1 | $FF
------+---------------------------------+-----
* = All columns to the right had filled up With 1s, so we carried to the
next column to the left.
Notice that when all of the "bit places" have a "1" in them, that the
total adds up to be 255 which is the maximum number that a Byte can hold.
In binary (the inner part of the Chart), "1" is the maximum value a bit
can hold Until it carries to the next column to the left. This brings us
to the next Chart, HEXIDECIMAL:
H E X I D E C I M A L
T A B L E
=========================================================================
Power| 1 0 |of 16 Power| 1 0 |of 16
-------+---------+----- -------+---------+-----
Decimal| | Decimal| |
Value| 16 0 | HEX Value| 16 0 | HEX
-------+---------+----- -------+---------+-----
0| 0 0 | 00ドル 31| 1 1 | 1ドルF
1| 0 1 | 01ドル * 32| 2 0 | 20ドル
2| 0 2 | 02ドル 33| 2 1 | 21ドル
3| 0 3 | 03ドル | |
4| 0 4 | 04ドル 47| 2 F | 2ドルF
5| 0 5 | 05ドル * 48| 3 0 | 30ドル
6| 0 6 | 06ドル 63| 3 F | 3ドルF
7| 0 7 | 07ドル * 64| 4 0 | 40ドル
8| 0 8 | 08ドル 79| 4 F | 4ドルF
9| 0 9 | 09ドル 80| 5 0 | 50ドル
10| 0 A | 0ドルA 95| 5 F | 5ドルF
11| 0 B | 0ドルB * 96| 6 0 | 60ドル
12| 0 C | 0ドルC 111| 6 F | 6ドルF
13| 0 D | 0ドルD * 112| 7 0 | 70ドル
14| 0 E | 0ドルE 127| 7 F | 7ドルF
15| 0 F | 0ドルF * 128| 8 0 | 80ドル
* 16| 1 0 | 10ドル 255| F F | $FF
17| 1 1 | 11ドル * 256| |0100ドル
-------+---------+----- -------+---------+-----
* = All columns to the right had filled up With 15 (F) so we carried
to the next column to the left.
The hexidecimal table is derived from BASE 16. The value that each column
may hold a value of 15 (F) before we carry to the next column. Also
notice that when both columns fill up With a value of "F" ($FF) that the
result is 255, which is the maximum For a Byte.
Okay, With that behind us, let's take a look at your application. As you
may have noticed in the binary table in the previous message, a Byte will
give us the ability to track up to 8 bits. Our goal here is to turn on or
off each of the 8 bits as each channel is turned on or off. I assume that
you've got 16 channels to work With, so we'll use a Word instead of a
Byte. When looked at in binary, a Word is like placing two Bytes
side-by-side. Notice that the HEXIDECIMAL works the same way.
256-------------------------+ +---------------------------- 128
512----------------------+ | | +------------------------- 64
1024-------------------+ | | | | +---------------------- 32
2048----------------+ | | | | | | +------------------- 16
4096-------------+ | | | | | | | | +---------------- 8
8192----------+ | | | | | | | | | | +------------- 4
16384-------+ | | | | | | | | | | | | +---------- 2
32768----+ | | | | | | | | | | | | | | +------- 1
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
Power | 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0|of 2
-------+------------------------------------------------+-------
Bit # | 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1|
-------+------------------------------------------------+-------
Decimal| |
Value| BINARY | HEX
-------+------------------------------------------------+-------
1| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1| 0001ドル
2| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0| 0002ドル
4| 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0| 0004ドル
8| 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0| 0008ドル
16| 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0| 0010ドル
32| 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0| 0020ドル
64| 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0| 0040ドル
128| 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0| 0080ドル
256| 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0| 0100ドル
512| 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0| 0200ドル
1024| 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0| 0400ドル
2048| 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0| 0800ドル
4096| 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0| 1000ドル
8192| 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0| 2000ドル
16384| 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0| 4000ドル
32768| 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0| 8000ドル
-------+------------------------------------------------+-------
Though it has taken us a While to get here, you now have a "value" for
each of your midi channels. if you need to use more than 16 channels, you
can use the same methods applied above using a LongInt to give you a total
of 32 channels (or bits).
You can now declare these as Constants in your Program like so:
}
Program MidiStuff;
Const
{Midi Channels}
Ch1 = 0001ドル;
Ch2 = 0002ドル;
Ch3 = 0004ドル;
Ch4 = 0008ドル;
Ch5 = 0010ドル;
Ch6 = 0020ドル;
Ch7 = 0040ドル;
Ch8 = 0080ドル;
Ch9 = 0100ドル;
Ch10 = 0200ドル;
Ch11 = 0400ドル;
Ch12 = 0800ドル;
Ch13 = 1000ドル;
Ch14 = 2000ドル;
Ch15 = 4000ドル;
Ch16 = 8000ドル;
Var
MidiChannels : Word;
{ Now you can turn on or off each channel and check to see if one is set by
using the following Procedures and Functions. You can accomplish this by
using the or and and operators. }
Function ChannelIsOn(Ch : Word) : Boolean;
begin
ChannelIsOn := (MidiChannels and Ch = Ch);
end;
Procedure TurnOnChannel(Ch : Word);
begin
MidiChannels := MidiChannels or Ch;
end;
Procedure TurnOffChannel(Ch : Word);
begin
MidiChannels := MidiChannels and not Ch;
end;
begin
MidiChannels := 0000ドル; {Initialize MidiChannels - No channels on!}
TurnOnChannel(Ch2);
if ChannelIsOn(Ch2) then
Writeln('Channel 2 is on!')
else
Writeln('Channel 2 is off!');
if ChannelIsOn(Ch3) then
Writeln('Channel 3 is on!')
else
Writeln('Channel 3 is off!');
TurnOnChannel(Ch16);
TurnOnChannel(Ch10);
TurnOffChannel(Ch2);
if ChannelIsOn(Ch2) then
Writeln('Channel 2 is on!')
else
Writeln('Channel 2 is off!');
end.