How to move bits of a number from register to eight other registers-CodePudding

I’m trying to move bits from starting register into eight consecutive registers. I’ve just started writing in assembly so I dont really know what to do.

I tried to use rol and lsr instructions. But my loop just reverses the bits. can i change the registry from r18 to r19 mid-loop?

.equ sequen = 0x10001011

ldi r17 
ldi r16, 0x8

next: lsr r17
rol r18    

             ;is there a way to move  
            ;to next register, not    
            ; inc its value?
dec r16
brbc 1, next
rjmp pc

CodePudding user response：

As say Peter Cordes it is possible. For example like this

.equ sequen = 0b1000_1011

        ldi r17, sequen
        ldi r16, 0x8

        ldi zl,18     ;Z (ZH:ZL) is used as indirect address register (pointer in C terminology)
        ldi zh,0      ;this two instruction set Z to 18 - address for first value. See AVR memmory map for details
        clr r0        
next:
        bst r17,0   
        bld r0, 0
        st  z , r0    ;save result to register and increase address (18, 19, ...|
        lsr r17
        dec r16
        brne next
        rjmp pc

CodePudding user response：

The pattern I would use in pseudo code is this.

You start with register V holding your 8 bit value, eg 0xe4 1110 0100

Set reg B to the bit pattern 0x01 Results go into R0 to R7

((V & (B << 0)) >> 0) & 0x01 goes into R0 (the bottom bit, ie bit 0) 0x00
((V & (B << 1)) >> 1)& 0x01 goes into R1 (the next bit, ie bit 1)   0x00
((V & (B << 2)) >> 2)& 0x01 goes into R2                            0x01
((V & (B << 3)) >> 3)& 0x01 goes into R3                            0x00
((V & (B << 4)) >> 4)& 0x01 goes into R4                            0x00
((V & (B << 5)) >> 5)& 0x01 goes into R5                            0x01
((V & (B << 6)) >> 6)& 0x01 goes into R6                            0x01
((V & (B << 7)) >> 7)& 0x01 goes into R7                            0x01

It could be loop where you left shift the initial bit pattern and then right shift the result of that by the shift value, then you move the result into memory location offset by the shiftvalue.

At the end of the loop, incr shiftValue and compare (or subtract) against end value jump conditionally to loop start.

loop:
  ((V & (B << ShiftValue)) >> ShiftValue) goes into Memory Shiftvalue
  ShiftValue subtract 0x80
  jump when zero loop: