SPUG: The bit pattern of a number (was sum-of-squares)

Mathew D. Watson matw at eclipse-optics.com
Mon Oct 6 08:20:04 CDT 2003


Thanks folks! This looks perfect.

--Mat

> -----Original Message-----
> From: spug-list-bounces at mail.pm.org
> [mailto:spug-list-bounces at mail.pm.org]On Behalf Of John W. Krahn
> Sent: Sunday, October 05, 2003 2:38 PM
> To: SPUG List
> Subject: Re: SPUG: The bit pattern of a number (was sum-of-squares)
> 
> 
> On Sunday 05 October 2003 10:51, Ben Reser wrote:
> > On Sun, Oct 05, 2003 at 09:57:34AM -0700, John W. Krahn wrote:
> > > $ perl -le'print scalar reverse unpack "b*", pack "d", 1'
> > > 0011111111110000000000000000000000000000000000000000000000000000
> > > $ perl -le'print scalar reverse unpack "b*", pack "d", -1'
> > > 1011111111110000000000000000000000000000000000000000000000000000
> > > $ perl -le'print scalar reverse unpack "b*", pack "d", 1e25'
> > > 0100010100100000100010110010101000101100001010000000001010010001
> > > $ perl -le'print scalar reverse unpack "b*", pack "d", 1e-25'
> > > 0011101010111110111100101101000011110101110110100111110111011001
> >
> > pack/unpack doesen't return the internal representation, but rather
> > the representation that you asked for via your format.  I.E. This
> > output may not match the output that perl actually was storing the
> > data in.  Which is what I think he was looking for.
> 
> It does if you use the correct formats:
> 
> $ perl -le'print unpack "B*", pack "S", 0b0001001000110100'
> 0011010000010010
> 
> That might be clearer using hexadecimal:
> 
> $ perl -le'print unpack "H*", pack "S", 0x1234'
> 3412
> 
> Which shows the little-endian representation on my Intel compatable
> machine.
> 
> 
> John
> -- 
> use Perl;
> program
> fulfillment
> 
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