"Stretching" a byte variable into two byte variables?


+ Reply to Thread
Results 1 to 10 of 10
  1. #1
    Join Date
    Feb 2013
    Posts
    753

    Default "Stretching" a byte variable into two byte variables?

    Hello
    I don't know the exact term I need, so here's what I'm doing. Since I've created custom 8x8 fonts for ST7920, I also want it to be able to display bigger letters too. Stretching vertically is not a problem - just double the lines and that's all. But when it comes to horizontal stretching, I'm facing some issues. The code should work as follows - initial bitmap data, read from single byte in eeprom, should be "stretched" into two byte variables and written to display. The code below shows how I see it. But it has a lot of if-then lines, and my guess is, that there should be a something simpler to do this task. Any ideas?

    Code:
    'bytes in eeprom at left, what should be at output - at right
    'this is a letter "A"
    'A		B	 C
    '(eeprom)	(MSB)	 (LSB)
    '00111100	00001111 11110000
    '01000010	00110000 00001100
    '01000010	00110000 00001100
    '01111110	00111111 11111100
    '01000010	00110000 00001100
    '01000010	00110000 00001100
    	
    IF A.0=0 THEN B.0=0:B.1=0
    IF A.0=1 THEN B.0=1:B.1=1
    IF A.1=0 THEN B.2=0:B.3=0
    IF A.1=1 THEN B.2=1:B.3=1
    IF A.2=0 THEN B.4=0:B.5=0
    IF A.2=1 THEN B.4=1:B.5=1
    IF A.3=0 THEN B.6=0:B.7=0
    IF A.3=1 THEN B.6=1:B.7=1
    
    
    IF A.4=0 THEN C.0=0:C.1=0
    IF A.4=1 THEN C.0=1:C.1=1
    IF A.5=0 THEN C.2=0:C.3=0
    IF A.5=1 THEN C.2=1:C.3=1
    IF A.6=0 THEN C.4=0:C.5=0
    IF A.6=1 THEN C.4=1:C.5=1
    IF A.7=0 THEN C.6=0:C.7=0
    IF A.7=1 THEN C.6=1:C.7=1

  2. #2
    Join Date
    May 2013
    Location
    australia
    Posts
    1,945

    Default Re: "Stretching" a byte variable into two byte variables?

    sample the msb of your byte
    if its set add three to your word var
    shift left the byte var 1 bit the word 2 bits
    repeat for all 8 bits
    This is more entertaining than Free to Air TV

  3. #3
    Join Date
    Feb 2013
    Posts
    753

    Default Re: "Stretching" a byte variable into two byte variables?

    and if it not?

  4. #4
    Join Date
    May 2013
    Location
    australia
    Posts
    1,945

    Default Re: "Stretching" a byte variable into two byte variables?

    don't add 3
    This is more entertaining than Free to Air TV

  5. #5

    Default Re: "Stretching" a byte variable into two byte variables?

    If you start off with B=0 and C=0 you can skip half those statements and only do the ones where A.x = 1

  6. #6
    Join Date
    Feb 2013
    Posts
    753

    Default Re: "Stretching" a byte variable into two byte variables?

    I wanted it to be shorter, by using loop and

    X.Y=Z
    but as I can see, you can't use another variable as bit reference, only static values.

  7. #7
    Join Date
    Feb 2013
    Posts
    753

    Default Re: "Stretching" a byte variable into two byte variables?

    uint16_t enlargeYourByte(uint8_t input)

    2 {

    3 uint16_t x = input;

    4 x = (x ^ (x << 4)) & 0x0f0f;

    5 x = (x ^ (x << 2)) & 0x3333;

    6 x = (x ^ (x << 1)) & 0x5555;

    7 return x | (x << 1));

    8 }



    This is how they do it in C. Can we port this to PBP ?

  8. #8
    Join Date
    Apr 2014
    Location
    Northeast
    Posts
    415

    Default Re: "Stretching" a byte variable into two byte variables?

    I think this does it:
    Code:
    Input VAR BYTE
    Wide VAR WORD
    X VAR WORD
    Y VAR WORD
    
    EnlargeYourByte:
    X = Input
    Y = Input << 4
    X = X ^ Y
    X = X & $0F0F
    Y = X << 2
    X = X ^ Y
    X = X & $3333
    Y = X << 1
    X = X ^ Y
    X = X & $5555
    Wide = X << 1
    RETURN

  9. #9
    Join Date
    May 2013
    Location
    australia
    Posts
    1,945

    Default Re: "Stretching" a byte variable into two byte variables?

    Code:
        any_byte=101011  ;eg input any_byte-> 10101011
        for any_cnt=0 to 7
        any_word=any_word<<2
        if  any_byte.7 then any_word=any_word+3
        any_byte=any_byte<<1
        next
    output any_word-> 1100110011001111


    mikes
    Code:
    X VAR WORD
    Y VAR WORD
    ;eg input any_byte-> 10101011
    
    
    X = ani_r
    Y = ani_r << 4
    X = X ^ Y
    X = X & $0F0F
    Y = X << 2
    X = X ^ Y
    X = X & $3333
    Y = X << 1
    X = X ^ Y
    X = X & $5555
    ani_h = X << 1
    output any_word-> 1000100010001010


    not working



    corrected

    Code:
    x = ani_r;
    x = (x ^ (x << 4)) & $0f0f;
    x = (x ^ (x << 2)) & $3333;
    x = (x ^ (x << 1)) & $5555;
    ani_h = x | (x << 1);

    and works , probably quicker the my loop
    Last edited by richard; - 25th October 2021 at 00:30.
    This is more entertaining than Free to Air TV

  10. #10
    Join Date
    May 2013
    Location
    australia
    Posts
    1,945

    Default Re: "Stretching" a byte variable into two byte variables?

    full test code here
    This is more entertaining than Free to Air TV

Similar Threads

  1. "Variable already an alias" - is there a way to avoid this?
    By CuriousOne in forum mel PIC BASIC Pro
    Replies: 24
    Last Post: - 20th August 2020, 06:48
  2. Byte from variable
    By Lilleljung in forum mel PIC BASIC Pro
    Replies: 2
    Last Post: - 14th February 2015, 23:29
  3. Replies: 0
    Last Post: - 14th November 2013, 04:32
  4. Replies: 3
    Last Post: - 15th October 2012, 09:06
  5. AN Question for "word" variable read The serial port
    By redfoen in forum mel PIC BASIC Pro
    Replies: 1
    Last Post: - 14th December 2007, 18:39

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts