Adding and reading byte variable from the bit array?

[CuriousOne]

Hello.
I'm upgrading my ST7920 "library", so letters can have variable width, for better visual appearance.
For this purpose, I plan to have single, screen-wide bit array, in which I will write the corresponding bits from the characters.
For this I will need the following

take say bits 2 to 5 from some byte variable and write them into bits 5 to 8 of bit array.
How should I?
One way I see is to make a loop, which will read bit by bit and write it bit by bit. But this is time consuming, and I believe, there should be faster ways to do this?
I know that I can do something like this buf[5]=char.1 which will write bit 1 of char variable into 5th position into buf array. But what about more "wide", several bit operations?

[mpgmike]

The best I can think of is shifting & bit masks. If you want to use bits 2 through 5, create a generic temporary variable to put the interim result. Right shift it to put the 1st needed bit at the 0 position, then AND mask it. The Temp variable will now be %0000 xxxx. Reverse the process for the destination variable using an OR mask first, then left shift it to put the key bits in %xxxx 0000.


SourceVar VAR BYTE
DestVar VAR BYTE
TempVar VAR BYTE

TempVar = (SourceVar >> 2) AND $0F
DestVar = (TempVar << 4) OR $F0

or maybe


DestVar = (SourceVar << 2) AND $F0

[mark_s]

Have you tried something like this?




Myword2.5 = Mybyte1.2 'move bit 2 of Mybyte1 to bit 5 Myword2
Myword2.6 = Mybyte1.3
Myword2.7 = Mybyte1.4
Myword2.8 = Mybyte1.5

[CuriousOne]

The issue is that these boundaries should be changeable, since different chars will have different pixel width.
There are two ways of doing this - all capitals have same width and all non-capital letters have another, smaller width. This indeed reduces some visual gaps, but not exactly what I want.
So my idea is to have a spare, "mask" byte for each character, which will define it's width and entry and exit points.
Say, there's "t", it is 4 pixels wide, and "mask" for it will look like this 00011110. zeros will be trimmed, and bits #5,4,3,2,1 from the letter shape will be added to output image.
Another, more complex idea, is to do it "ZX Spectrum way", via complex STR/MID/LEN/ASC and other statements, currently not implemented, but still doable, in PBP....

[CuriousOne]

FOR X=1 to 5
Y=Z.X
NEXT

As I understand, such operation is not possible in PBP, I mean, it is not possible to substitute variable as a bit part identifier for another variable?

[richard]

As I understand, such operation is not possible in PBP, I mean, it is not possible to substitute variable as a bit part identifier for another variable?

where did you get that idea, it is very possible with the correct syntax

suggest a read of the manual re

Applying Offsets to Bits within a Variable or Register

[CuriousOne]

I didn't get the idea, I just tried it and it gives syntax error......