That is true if you can tell at *compile time* that the divisor is a power of
2. On the other hand if the divisor is an indeterminate that is constrained to
be a power of 2 then you have to do the shift on your own.
/* *********************** Example (Before) ************************** */
public int getRandomPowerOfTwo( Random random )
{
// gets 5 bit int ( value between 0 and 31 )
int power = random.next( 5 );
// 2 raised to 31 is beyond the int range
// so get another instead
while( power == 31 )
{
power = random.next( 5 );
}
return 1 << power;
}
public int processValue( int value )
{
Random random = new Random();
// following division not converted to shift
return value / getRandomPowerOfTwo( random );
}
/* *********************** Example (After) ************************** */
public int getRandomPowerOfTwoExponent( Random random )
{
// gets 5 bit int ( value between 0 and 31 )
int power = random.next( 5 );
// 2 raised to 31 is beyond the int range
// so get another instead
while( power == 31 )
{
power = random.next( 5 );
}
return power;
}
public int processValue( int value )
{
Random random = new Random();
// following division performed by explicit shift
return value >> getRandomPowerOfTwoExponent( random );
}
/* ****************************************************************** */
-- Roger Glover
--- Joseph Ottinger <[EMAIL PROTECTED]> wrote:
> Actually, nearly every modern compiler will optimize divisions by powers of
> two *into* bit shifts, so >> isn't faster than / at all... unless your
> compiler/optimizer is retarded.
>
>
> >From: "Paul Franz" <[EMAIL PROTECTED]>
> >Reply-To: "JDJList" <[EMAIL PROTECTED]>
> >To: "JDJList" <[EMAIL PROTECTED]>
> >Subject: [jdjlist] Re: Shift Operator: What is it good for?
> >Date: Thu, 5 Sep 2002 14:40:06 -0400
> >
> >Shift Operator: What is it good for?Dividing by a multiple of 2. This is
> >faster than using the / operator.
> >
> >Paul Franz
> > ----- Original Message -----
> > From: Hansen, Knud
> > To: JDJList
> > Sent: Thursday, September 05, 2002 2:19 PM
> > Subject: [jdjlist] Shift Operator: What is it good for?
> >
> >
> > During the discussion about 'Getting digits from an integer' there was a
> >reference to the binary shift operator >>. In my 15 years of programming I
> >have never once used the shift operator. I am sure it must be used for
> >something, but I can not think of anything useful. Anybody out there every
> >use it? If so, what for?
> >
> > Thanks
> > Knud Hansen
> >
> >
> >
> >
> >
> > To change your JDJList options, please visit:
> >http://www.sys-con.com/java/list.cfm
> >
> >
> >To change your JDJList options, please visit:
> >http://www.sys-con.com/java/list.cfm
>
>
> -----------------------------------------------
> Joseph B. Ottinger [EMAIL PROTECTED]
> http://enigmastation.com IT Consultant
>
> _________________________________________________________________
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=====
-- Roger Glover
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