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counting digits

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counting digits

Dec 14th, 2006

Does anyone knows how can I count how many digits are there in a binary number? Any ideas???

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Re: counting digits

Dec 14th, 2006

create a loop that repeatedly divides the value by 10 until its value becomes 0. increment a counter on each loop iteration. see the description for the idiv instruction if you do not know what it does.

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Re: counting digits

Dec 14th, 2006

You would need to convert the binary number to an integer first for that though, wouldn't you?

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Re: counting digits

Dec 14th, 2006

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Originally Posted by cscgal

You would need to convert the binary number to an integer first for that though, wouldn't you?

binary numbers are either signed or unsigned integers. No conversion necessary.

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Re: counting digits

Dec 14th, 2006

I'm thinking of a binary number being stored as a string. Nevermind.

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Re: counting digits

Dec 17th, 2006

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Originally Posted by kiks

Does anyone knows how can I count how many digits are there in a binary number? Any ideas???

From what I understand, you want to count the number of digits in binary form, ex. 10001 (decimal 17) has 5 digits. You simply test the most significant towards least significant bits untill you reach a bit that is set on or 1. Total bits minus that count is the number of digits, example would be a 16bit register and a 0000000000010001 binary will give you 11 as your count (as theres 11 zeros). So 16-11 = 5. If you want the number of digits in base 10 then refer to the previous posts.

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Re: counting digits

Jan 4th, 2007

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Originally Posted by Ryu

From what I understand, you want to count the number of digits in binary form, ex. 10001 (decimal 17) has 5 digits. You simply test the most significant towards least significant bits untill you reach a bit that is set on or 1. Total bits minus that count is the number of digits, example would be a 16bit register and a 0000000000010001 binary will give you 11 as your count (as theres 11 zeros). So 16-11 = 5. If you want the number of digits in base 10 then refer to the previous posts.

How do i test the most/last significant bits of register?
In a general, is there list of all assembly functions available somewhere on web, i haven't found one ?

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Re: counting digits

Jan 7th, 2007

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Originally Posted by vov4ik

How do i test the most/last significant bits of register?
In a general, is there list of all assembly functions available somewhere on web, i haven't found one ?

You use the TEST instruction, I'm assuming that you are working with IA32 architecture.

Example:

 Help with Code Tags 
 Assembly Syntax (Toggle Plain Text) 
mov ax, myBinaryValue
mov dx, 0000000000000001b  ; first ROR will make this most significant bit
mov cx, 16  ; 16 bits
 
LOOP:
ror   dx, 1   ; rotate bits to the right by 1
test  dx, ax ; this test will set ZF=0 (not zero) when the a bit is found on
jnz   BITFOUND
dec  cx       ; decrease bit count
jnz   LOOP  ; test again
 
;;;; if program enters here myBinaryValue is zero ;;;;
 
BITFOUND:
 
;;;; if program enters here a bit set on was found ;;;;
;;;; number of digits should be in CX register ;;;
mov ax, myBinaryValue
mov dx, 0000000000000001b  ; first ROR will make this most significant bit
mov cx, 16  ; 16 bits
 
LOOP:
ror   dx, 1   ; rotate bits to the right by 1
test  dx, ax ; this test will set ZF=0 (not zero) when the a bit is found on
jnz   BITFOUND
dec  cx       ; decrease bit count
jnz   LOOP  ; test again
 
;;;; if program enters here myBinaryValue is zero ;;;;
 
BITFOUND:
 
;;;; if program enters here a bit set on was found ;;;;
;;;; number of digits should be in CX register ;;;

Note: this program was never tested.

Last edited by Ryu; Jan 7th, 2007 at 12:49 pm.

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Re: counting digits

Jan 8th, 2007

 Help with Code Tags 
 Assembly Syntax (Toggle Plain Text) 
;
; Assuming 386 32 bit assembler code
;
   mov ecx,val 
   xor eax,eax  ; Counts the number of '1' bits
 
again:
   shl ecx,1
   adc eax,0
   or ecx,ecx
   jnz again
 
done:
;
; EAX has the count of bits in "val"
;
;
; Assuming 386 32 bit assembler code
;
   mov ecx,val 
   xor eax,eax  ; Counts the number of '1' bits

again:
   shl ecx,1
   adc eax,0
   or ecx,ecx
   jnz again

done:
;
; EAX has the count of bits in "val"
;