bits - Xtreme Visual Basic Talk

05-12-2002, 01:30 PM

n2amg

Junior Contributor

Join Date: Aug 2001

Posts: 235

bits

I need a tutorial on bits... I need to enter various numbers into the following bit locations but I don't know how to figure what goes where...

here is the message I send to the application:
PostMessage MMTY_HWND, MMTTY_MSG, RXM_SETVIEW, xxyy

where xxyy is the following

b0-b2 Display width of FFT spectrum
b4-b5 FFT gain
b6-b7 FFT response time
b8 XY scope size
b10-b11 XY scope quality
b12 XY scope display on/off
b13 FFT gain test mode

Also will someone explain to me this upper16 bit and lower 16 bit
again using the same format post message

PostMessage MMTY_HWND, MMTTY_MSG, RXM_WINPOS, xxyy

lParam (upper 16 bits) = Y-axis position (screen pixel value)
lParam (lower 16 bits) = X-axis position (screen pixel value)

Thanks
Rick

05-12-2002, 01:36 PM

Squirm

Political Coder

Retired Moderator
* Guru *

Join Date: Mar 2001

Location: London, England

Posts: 8,037

You can alter a bitmask with Or and And Not.

The bits are:

Code:

0 - 1       8 - 256
1 - 2       9 - 512
2 - 4       10 - 1024
3 - 8       11 - 2048
4 - 16      12 - 4096
5 - 32      13 - 8192
6 - 64      14 - 16384
7 - 128     15 - 32768

So if you wanted to turn bit 5 on, you would do:

Number = Number Or 32

If you wanted to turn bit 14 off, you would do:

Number = Number And (Not 16384)

__________________
Search the forums | Use [vb][/vb] tags | Still IRCing

05-12-2002, 01:42 PM

Banjo

Hell's Angel

Retired Moderator
* Guru *

Join Date: Jul 2001

Location: Yorkshire, UK

Posts: 10,394

A long is a 32-bit number. That is 32 binary digits. The x and y co-ordinates only need 16 bits each, so they have been combined into one 32 bit number.
In this case the 16 bit Y is assigned to the upper 16 bits of the 32 bit long. The 16 bit X is assigned to the lower 16 bits of the 32 bit number.

In base 2 (binary) multiplying by 2 shifts the bits to one the left. That is you multiple by 2^1. To shift 2 places you multiple by 2 twice. Ie 2^2.

So to get the y co-ord in to the upper 16 bits you need to multiple by 2 ^ 16. You need add then OR in the lower 16 bits (the x co-ord).

So the code you want is:

Code:

Function Make32BitNum(ByVal iUpper As Integer, ByVal iLower As Integer) As Long
    Make32BitNum = (iUpper * 2 ^ 16) Or iLower
End Function

__________________
A wise one man once said "what you talking about dog breath"

05-12-2002, 01:48 PM

Banjo

Hell's Angel

Retired Moderator
* Guru *

Join Date: Jul 2001

Location: Yorkshire, UK

Posts: 10,394

Also remember that signed numbers (as all numbers in VB are) use a scheme called two's complement. Basically to get the negative version of a number you invert it and then add 1. So to invert 12 you'd have this:

12 = 00001100

invert to gives the negative in 1's complement:

-12 = 11110011

then add one to give the negative in 2's complement:

-12 = 11110100

Note that for all negative numbers the leftmost bit is zero bits is 1 and for all positive numbers the leftmost bit is 0.

To work out a negative number from the bit pattern you have to take the ordinal value of the leftmost bit, invert it and then add the ordinal values of the other bits that are 1:

11110100 = -128 + 64 + 32 + 16 + 4 = -12

__________________
A wise one man once said "what you talking about dog breath"