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Multiplication and shif operator

ather ali

Joined: Nov 08, 2001
Posts: 15
hi guys
can any one tell me how computer can multipy internally any number with 3,6,7,9 etc
cuz if u multiply any number with two that means
number << 1;
number << 2 // means multiplied by 4
number << 3 // means multipled by 8
how i can multipy a number with 3 5 7 etc
i hope u have understood my question..
Marilyn de Queiroz

Joined: Jul 22, 2000
Posts: 9056
This question has nothing to do with Programmer Certification. I'm moving it to Java in General(intermediate).

"Yesterday is history, tomorrow is a mystery, and today is a gift; that's why they call it the present." Eleanor Roosevelt
Rob Ross

Joined: Jan 07, 2002
Posts: 2205
In a modern binary computer, you can only use the integer value and multiply using decimal arthimetic, ie,
int i = 3;
i = i*3 ;// multiply by three
i = i * 5; //multiply by five
There's no bit-shifting trick for these. The "trick" only works for powers of two, because it's in Base-2.
Think about the same thing in the decimal system when multiplying by powers of 10...since we use base ten this is as simple as shifting over the digits and adding a zero on the end...
112 << 1 : multiplying by 10 "shifts" digits one time to left
(These are pretend - java doesn't have Base-10 shifting, but this is how it would look if it did )
112 << 1 = 1120 //multiplied by 10
13 << 2 = 1300 //mutliplied by 100
But the answer to your question is "you cant."
[ April 18, 2002: Message edited by: Rob Ross ]

SCJP 1.4
John Lee
Ranch Hand

Joined: Aug 05, 2001
Posts: 2545
Hardware-wise, I think computer calculate each binary byte from right to left.
I agree. Here's the link:
subject: Multiplication and shif operator
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