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Mine doesn't work? uhh I think it works perfectly.

.586

.model flat, stdcall

OPTION SCOPED

OPTION CASEMAP:NONE



INCLUDE \masm32\include\kernel32.inc

INCLUDELIB \masm32\lib\kernel32.lib

INCLUDE \masm32\include\user32.inc

INCLUDELIB \masm32\lib\user32.lib



.DATA



    notp2 DB "Not", 0

    yesp2 DB "Yes", 0

    value DD 6



.CODE



Start:



    mov eax,value 

    test eax,1

    je @PowerOfOne



    ;mov edx,value

    ;mov eax,value

    ;dec eax

    ;and eax, edx    

    ;jnz @PowerOfOne

    

    invoke  MessageBox, 0, OFFSET yesp2, 0, 0

    jmp @@Exit

    

    @PowerOfOne:

    

    invoke  MessageBox, 0, OFFSET notp2, 0, 0

    

    @@Exit:

    

    invoke  ExitProcess, 0



END Start    

Compile this proggy to test and try replacing the value with 5. This will popup yes (meaning 5 is a power of 2) :)

Hello Stryker !

I didn't write anything about your code didn't work!

I only pointed out that:


am I missing something here 4 = 1000 ?
isn't the binary number of 4 = 0100
and the binary number of 3 = 0011


Regards,

The SharK

http://home19.inet.tele.dk/assembler

;)

This one will determine if a value is root of 2. Not the power of 2. :)

[size=9]

.586

.MODEL FLAT, STDCALL

OPTION SCOPED

OPTION CASEMAP:NONE



INCLUDE \masm32\include\kernel32.inc

INCLUDELIB \masm32\lib\kernel32.lib

INCLUDE \masm32\include\user32.inc

INCLUDELIB \masm32\lib\user32.lib



.DATA



    notp2 DB "Not", 0

    yesp2 DB "Yes", 0

    

    value REAL8 16.0



.CODE



Start:



    fld value

    fsqrt

    fstp value

    fld value

    frndint

    fcomp value

    fstsw ax

    sahf

    fstp value  ;Rebalance FPU stack

    jne @@NotPowerOf2

    

        invoke MessageBox, 0, OFFSET yesp2, 0, 0

        jmp @@Exit

    

    @@NotPowerOf2:

        

        invoke MessageBox, 0, OFFSET notp2, 0, 0

        

    @@Exit:

    

    invoke  ExitProcess, 0



END Start    

[/size]

; Value to test in eax

; We will splatter ecx, so make sure nothing in there!



bsf ecx, eax

jnz NoBitsSet



btr eax, ecx

bsf ecx, eax



jnz PowerOfTwo

If you count zero as a power of 2, then you can get rid of the "jnz NoBitsSet"...

Beware, this code will be quite slow on anything less than a PPro/P2!

----- Edit -----
Alternative (non-destructive)

bsf ecx, eax

;jnz NoBitsSet ;Optional

bsr edx, eax

cmp edx, ecx

jne NonPowerOfTwo

As for BitRAKEs method, why not:

PowerOfTwo MACRO regmem:REQ

;; return EAX zero if regmem is a power of two

    mov eax, regmem

;    mov edx, regmem ;Not needed

    dec eax

    sbb edx,edx

    and eax, regmem

    xor eax, edx

ENDM

Or even:

mov edx, eax

dec eax

and eax, edx

; eax zero of powers of 2, non-zero for not

Mirno

Simple

;on exit if number is a power of two,

;eax = zero,  otherwise eax = non zero

;

;

mov eax, number		;load number to test





bsf ecx, eax		;find position of 1st on bit

			;if no bits present, eax = 0



shr eax, cl		;shift the bit down

			;if eax = 0 this does nothing.



dec eax			;if there was only 1 bit, eax = 1

			; so dec eax would be zero

Traditionally a non-zero value is TRUE, so you'd have to call this proc IsNotPowerOfTwo() for it to make sense. ;)

hmm! I tested that algo but it returned something that it shouldn't.

- Number 0 it returned 0. 0 is a power of 2 ==> 0^2 = 0.
- Number 8 it returned 1. 8 is a power of 3 ==> 2^3 = 8.
- Number 9 it returned 0. 9 is a power of 2 ==> 3^2 = 9.

This is also where my first code fell(check the first reply). The numbers 0, 8 and 9 always screws up my first algo. The last stable solution I tested was the FPU code.

Oh sorry what was I thinking :) Geez!!! I need to clear my head :) Since I got caught with the functions i'm creating right now on determining n power. :)


I mistook it as power of x it should be root of x. :)