Very basic bytes

[rams]

Can somebody help me in recognizing the binary values ??

I've read that 11111000 is equal to -8. I understand the reason is because the high order bit is 1.
Why shud it not be interpreted as -120 ?? And if at all I need to write -120 in binary form how shud
I go about it ??

Thanks,
rams

[poochi]

To find the binary value for negative numbers , do the following..

for -8 :

1. +8's binary value minus one..


00000....1000 -1 = 00000.... 0111




2. Take 2's (1's ? ) compliment of the result.



11111.... 1000 = -8





for -120 :

1. +120's binary value minus one



0000... 0111 1000 - 1 = 0000... 0111 0111




2. 2's(1's?) compliment of the result.. ( 0 becomes 1 and 1 becomes 0 )



1111.... 1000 1000 = -120






Poochi..

[rams]

Dear Poochi,

thanks for responding to my question.
but i am still confused. could you please explain me a little bit on the following.

i understood how to convert numbers to negative using 2's complement and adding 1 to the result.
but incase somebody gives me the number say 1111 1000 and asks me what it represents i will go with
the idea that because the high order bit is 1 its a negative number and calculating the value frm the
remaining numbers its 120. so i will end up saying -120 which is not true. can u help me with this ??

thanks,
rams.

[poochi]

Hi Ram,

In 2's compliment notation , the higher order bit always represent negative value.
If you see 1 in the higher order bit you can assume that the binary value represent
a negative number and you can proceed with that assumption.

> but incase somebody gives me the number say 1111 1000 and asks me what it represents i will go with
> the idea that because the high order bit is 1 its a negative number and calculating the value frm the
> remaining numbers its 120. so i will end up saying -120 which is not true. can u help me with this ??

How did you get the number 120 from 1111 1000 ? you have to do the reverse engg. here..
O.K if the higher order bit is 1 , then you can assume that the number is negative ,right ?

Take 1's compliment of it and add 1 with the result ( shortly , we can say 2's compliment )



1111 1000 -> 1's Compliment -> 0000 0111 + 1 -> 0000 1000 = 8




I know it's a negative number. So , it's -8.

Check the output of the following program



class Binary{
public static void main( String[] str ){
int i = 0x80000000;
System.out.println( i );
}
}





You will get the following output..



-2147483648





The bit pattern is



1000 0000 0000 0000 0000 0000 0000 0000





Since the 2's compliment's higher order bit always represent signed value , it's a negative
number. Take 2's compliment of it ( you will get the same bit value ) and convert it
to decimal and put minus infront of it.

I hope i am not confusing you..

Poochi..