 |
 |
| View previous topic :: View next topic |
| Author |
Message |
vtrx
Joined: 11 Oct 2017
Posts: 142
|
| Shift a byte with carry to another |
 Posted: Sun Jul 25, 2021 6:08 am |
 |
|
I'm using 8x8 modules from China that are already connected to each other (4).
I want to do the scroll effect, but these modules have different connections.
I came up with a simple solution, but I depend on some expressions.
How do I shift a byte to the left, take the MSB bit of another byte, along with the shifted first, and shift the other one?
I hope you understand me, English is not my first language. |
|
 |
Ttelmah
Joined: 11 Mar 2010
Posts: 19515
|
|
| Posted: Sun Jul 25, 2021 6:55 am |
|
|
Look at the shift_left function.,
For example:
| Code: |
char buffer[4];
int1 bit_to_add=1;
buffer[0]=0x80;
buffer[1]=0xAA;
buffer[2]=0;
buffer[3]=0;
shift_left(buffer,4,bit_to_add);
|
This shifts the 4 bytes of 'buffer' left one bit, and shifts 'bit_to_add' into the
rightmost bit. So you would have:
0x00015501
You can specify how many bytes it is to move (this is the 4), and what is
in 'bit_to_add' gets shifted in to the bottom of the sequence.. |
|
|
vtrx
Joined: 11 Oct 2017
Posts: 142
|
|
| Posted: Sun Jul 25, 2021 7:20 am |
|
|
follows a hypothetical example.
| Code: |
letter x:
1000 0000
1010 1010
0000 0000
1000 0000
letter y:
1000 0101
1111 1111
0101 0101
1001 1001
The expected result:
letter x:
0000 0001
0101 0101
0000 0000
0000 0001
letter y:
0000 1010
1111 1110
1010 1010
0011 0010
|
|
|
|
Ttelmah
Joined: 11 Mar 2010
Posts: 19515
|
|
| Posted: Sun Jul 25, 2021 10:44 am |
|
|
That seems to just be showing four individual byte shifts with no
carry between the bytes and zero shifted in at the right.
There is no carry in what you show.
That should be:
| Code: |
char buffer[4];
int1 bit_to_add=0;
buffer[0]=0x80;
buffer[1]=0xAA;
buffer[2]=0;
buffer[3]=0x80;
shift_left(&buffer[0],1,bit_to_add);
shift_left(&buffer[1],1,bit_to_add);
shift_left(&buffer[2],1,bit_to_add);
shift_left(&buffer[3],1,bit_to_add);
|
|
|
|
vtrx
Joined: 11 Oct 2017
Posts: 142
|
|
| Posted: Sun Jul 25, 2021 2:33 pm |
|
|
I actually need to shift right.
I got the expected result, but the routine is not optimized because it is 128 bytes.
it basically starts like this:
| Code: |
for(d=0;d<8;d++)
{
scroll_buf[d+16]=scroll_buf[d+16]>>1;
if(bit_test(scroll_buf[d+8],0)==1){bit_set(scroll_buf[d+16],7);}
scroll_buf[d+8]=scroll_buf[d+8]>>1;
if(bit_test(scroll_buf[d],0)==1){bit_set(scroll_buf[d+8],7);}
scroll_buf[d]=scroll_buf[d]>>1;
} |
| Code: | letter x: letter y: result x: result y:
1000 0000 -> 1000 0101 = 0100 0000 0100 0100
1010 1010 -> 1111 1111 = 0101 0101 0111 1111
0000 0000 -> 0101 0101 = 0000 0000 0010 1010
1000 0000 -> 1001 1001 = 0100 1000 0100 1100 |
|
|
|
PCM programmer
Joined: 06 Sep 2003
Posts: 21708
|
|
| Posted: Sun Jul 25, 2021 3:00 pm |
|
|
Your coding efficiency is not the greatest.
| Quote: | scroll_buf[d+16]=scroll_buf[d+16]>>1;
|
The line above (from your program) creates this list file code:
| Code: |
.................... scroll_buf[d+16]=scroll_buf[d+16]>>1;
000C2: MOVLW 10
000C4: ADDWF d,W
000C6: CLRF @03
000C8: ADDLW scroll_buf
000CA: MOVWF @01
000CC: MOVLW scroll_buf+-5
000CE: ADDWFC @03,F
000D0: MOVFF 03,@@57
000D4: MOVLW 10
000D6: ADDWF d,W
000D8: CLRF @03
000DA: ADDLW scroll_buf
000DC: MOVWF FSR0L
000DE: MOVLW scroll_buf+-5
000E0: ADDWFC @03,W
000E2: MOVWF FSR0H
000E4: BCF STATUS.C
000E6: RRCF INDF0,W
000E8: MOVFF @@57,FSR0H
000EC: MOVFF 01,FSR0L
000F0: MOVWF INDF0
|
But an equivalent way to write that line is shown below:
| Code: | scroll_buf[d+16] >>= 1;
|
It produces a much shorter (and faster) amount of ASM code:
| Code: |
.................... scroll_buf[d+16] >>= 1;
0013C: MOVLW 10
0013E: ADDWF d,W
00140: CLRF @03
00142: ADDLW scroll_buf
00144: MOVWF FSR0L
00146: MOVLW scroll_buf+-5
00148: ADDWFC @03,W
0014A: MOVWF FSR0H
0014C: BCF STATUS.C
0014E: RRCF INDF0,W
|
|
|
|
vtrx
Joined: 11 Oct 2017
Posts: 142
|
|
| Posted: Sun Jul 25, 2021 4:49 pm |
|
|
With your tip, i'm trying to optimize the code even more, but i can't fit another loop.
Do you have an idea?
| Code: | for(d=0;d<8;d++)
{
scroll_buf[d+256]>>=1;
if(bit_test(scroll_buf[d+248],0)==1){bit_set(scroll_buf[d+256],7);}
scroll_buf[d+248]>>=1;
if(bit_test(scroll_buf[d+240],0)==1){bit_set(scroll_buf[d+248],7);}
scroll_buf[d+240]>>=1;
if(bit_test(scroll_buf[d+232],0)==1){bit_set(scroll_buf[d+240],7);}
scroll_buf[d+232]>>=1;
if(bit_test(scroll_buf[d+224],0)==1){bit_set(scroll_buf[d+232],7);}
scroll_buf[d+224]>>=1;
if(bit_test(scroll_buf[d+216],0)==1){bit_set(scroll_buf[d+224],7);}
scroll_buf[d+216]>>=1;
if(bit_test(scroll_buf[d+208],0)==1){bit_set(scroll_buf[d+216],7);}
scroll_buf[d+208]>>=1;
if(bit_test(scroll_buf[d+200],0)==1){bit_set(scroll_buf[d+208],7);}
scroll_buf[d+200]>>=1;
if(bit_test(scroll_buf[d+192],0)==1){bit_set(scroll_buf[d+200],7);}
scroll_buf[d+192]>>=1;
if(bit_test(scroll_buf[d+184],0)==1){bit_set(scroll_buf[d+192],7);}
scroll_buf[d+184]>>=1;
if(bit_test(scroll_buf[d+176],0)==1){bit_set(scroll_buf[d+184],7);}
scroll_buf[d+176]>>=1;
if(bit_test(scroll_buf[d+168],0)==1){bit_set(scroll_buf[d+176],7);}
scroll_buf[d+168]>>=1;
if(bit_test(scroll_buf[d+160],0)==1){bit_set(scroll_buf[d+168],7);}
scroll_buf[d+160]>>=1;
if(bit_test(scroll_buf[d+152],0)==1){bit_set(scroll_buf[d+160],7);}
scroll_buf[d+152]>>=1;
if(bit_test(scroll_buf[d+144],0)==1){bit_set(scroll_buf[d+152],7);}
scroll_buf[d+144]>>=1;
if(bit_test(scroll_buf[d+136],0)==1){bit_set(scroll_buf[d+144],7);}
scroll_buf[d+136]>>=1;
if(bit_test(scroll_buf[d+128],0)==1){bit_set(scroll_buf[d+136],7);}
scroll_buf[d+128]>>=1;
if(bit_test(scroll_buf[d+120],0)==1){bit_set(scroll_buf[d+128],7);}
scroll_buf[d+120]>>=1;
if(bit_test(scroll_buf[d+112],0)==1){bit_set(scroll_buf[d+120],7);}
scroll_buf[d+112]>>=1;
if(bit_test(scroll_buf[d+104],0)==1){bit_set(scroll_buf[d+112],7);}
scroll_buf[d+104]>>=1;
if(bit_test(scroll_buf[d+96],0)==1){bit_set(scroll_buf[d+104],7);}
scroll_buf[d+96]>>=1;
if(bit_test(scroll_buf[d+88],0)==1){bit_set(scroll_buf[d+96],7);}
scroll_buf[d+88]>>=1;
if(bit_test(scroll_buf[d+80],0)==1){bit_set(scroll_buf[d+88],7);}
scroll_buf[d+80]>>=1;
if(bit_test(scroll_buf[d+72],0)==1){bit_set(scroll_buf[d+80],7);}
scroll_buf[d+72]>>=1;
if(bit_test(scroll_buf[d+64],0)==1){bit_set(scroll_buf[d+72],7);}
scroll_buf[d+64]>>=1;
if(bit_test(scroll_buf[d+56],0)==1){bit_set(scroll_buf[d+64],7);}
scroll_buf[d+56]>>=1;
if(bit_test(scroll_buf[d+48],0)==1){bit_set(scroll_buf[d+56],7);}
scroll_buf[d+48]>>=1;
if(bit_test(scroll_buf[d+40],0)==1){bit_set(scroll_buf[d+48],7);}
scroll_buf[d+40]>>=1;
if(bit_test(scroll_buf[d+32],0)==1){bit_set(scroll_buf[d+40],7);}
scroll_buf[d+32]>>=1;
if(bit_test(scroll_buf[d+24],0)==1){bit_set(scroll_buf[d+32],7);}
scroll_buf[d+24]>>=1;
if(bit_test(scroll_buf[d+16],0)==1){bit_set(scroll_buf[d+24],7);}
scroll_buf[d+16]>>=1;
if(bit_test(scroll_buf[d+8],0)==1){bit_set(scroll_buf[d+16],7);}
scroll_buf[d+8]>>=1;
if(bit_test(scroll_buf[d],0)==1){bit_set(scroll_buf[d+8],7);}
scroll_buf[d]>>=1;
} |
|
|
|
Ttelmah
Joined: 11 Mar 2010
Posts: 19515
|
|
| Posted: Mon Jul 26, 2021 4:05 am |
|
|
You are just using an 8 element loop, and then doing this for every eighth
element. Why not just loop from 256?. So something like:
| Code: |
void scroll(int16 index)
{
scroll_buf[index] >>= 1;
if(bit_test(scroll_buf[index-8],0)==1)
scroll_buf[index]+=128;
}
for(d=256;d>=0;d--)
{
scroll(d);
}
//d has to be a signed int16 to use like this
|
To deal with the bottom eight elements I add a test to ensure it doesn't
start trying to pull in the carry from below zero. |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
FAQ 
Search
Register
Profile 
Log in to check your private messages 
Log in
