Hi,

the code in your attachment sqrt32_Fb.txt  looks different compared to 
the one at 
https://www.mikrocontroller.net/articles/AVR_Arithmetik#Wurzel

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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

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;  Fast and short 32 bits AVR sqrt routine, avr-gcc ABI compliant

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;  R25:R24 = SQRT (R25:R24:R23:R22)

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;  rounded down to integer

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;     Destroys R26,R27,R22,R23,R18,R19

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;  Cycles incl call & ret = 260-300

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;  Stack incl call = 2-3

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.text

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.global sqrt32_floor

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.type sqrt32_floor, @function

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sqrt32_floor:

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    ldi   R19, 0xc0

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    clr   R18               ; rotation mask in R19:R18

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    ldi   R27, 0x40

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    sub   R26, R26          ; developing sqrt in R27:R26, C=0

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1:  brcs  2f                ; C --> Bit is always 1

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    cp    R24, R26

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    cpc   R25, R27          ; Does test value fit?

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    brcs  3f                ; C --> nope, bit is 0

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2:  sub   R24, R26

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    sbc   R25, R27          ; Adjust argument for next bit

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    or    R26, R18

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    or    R27, R19          ; Set bit to 1

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3:  lsr   R19

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    ror   R18               ; Shift right mask, C --> end loop

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    eor   R27, R19

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    eor   R26, R18          ; Shift right only test bit in result

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    rol   R22               ; Bit 0 only set if end of loop

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    rol   R23

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    rol   R24

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    rol   R25               ; Shift left remaining argument (C used at 1:)

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    sbrs  R22, 0            ; Skip if 15 bits developed

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    rjmp  1b                ; Develop 15 bits of the sqrt

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    brcs  4f                ; C--> Last bits always 1

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    lsl   R23               ; Need bit 7 in C for cpc

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    cpc   R26, R24

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    cpc   R27, R25          ; After this C is last bit

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4:  adc   R26, R19          ; Round up if C (R19=0)

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    mov   R25, R27          ; return in R25:R24 as for avr-gcc ABI

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    mov   R24, R26

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    ret

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.size sqrt32_floor, .-sqrt32_floor

Ok, thanks

but where is jump locations ?

see line 16, brcs 2f
see line 20, brcs 3f

assembler shows an error on this instructions

Kishor S. wrote:

> Ok, thanks
>
> but where is jump locations ?
>
> see line 16, brcs 2f
> see line 20, brcs 3f
>
> assembler shows an error on this instructions

These notations are from C inline assembly language, which is very 
different from an directly usable assembly language.

The understanding of this crude notation is simple: the number describes 
the relative branch distance (in instruction words), the trailing 
character denotes, if it is a forward branch or a backward branch. Of 
course the 'f' stands for 'forward'.

So your task is: count instruction words up from the branch instruction 
and insert a label at found point in source code. Finally replace the 
branch target parameter by the name of this label.

C-hater wrote:
> The understanding of this crude notation is simple: the number describes
> the relative branch distance (in instruction words), the trailing
> character denotes, if it is a forward branch or a backward branch. Of
> course the 'f' stands for 'forward'.
>
> So your task is: count instruction words up from the branch instruction
> and insert a label at found point in source code. Finally replace the
> branch target parameter by the name of this label.

That's so wrong, even the opposite wouldn't be any better!

1f or 1b (or any other number) simply points to a numbered label in 
forward or backward direction.

Thanks a lot,

I learn this new thing, after 25 yrs. of coding practice..........

after so many efforts, I can't be able to assemble this code in assembly 
language.

I cant interpret this keyword
"brcs 2f"
"brcs 2b"
and
sbrs R22,0 (at line 33)

can anyone explain ?