[Tutor] Applying a mask

[Kirby Urner]

At 04:13 PM 11/21/2001 +0100, you wrote:


>Dear all,
>
>I have a string, containing a 63-digit hexadecimal number.
>I want to build a function which extracts bits from that
>hexadecimal number, and show it as an integer (unsigned)
>value.

The long integer is a place to store big hex numbers.
In Python 2.2, we're starting to not need to specify
when an integer is long, with the 'L' suffix.

   >>> myhex = eval('0x'+'A323332BFE23231')
   >>> myhex
   734705982275465777L

eval('0x'+yourstring) will need to be written
eval('0x'+yourstring+'L') if your Python is < 2.2.

Then you can AND this with another long.

   >>> hex2 = eval('0x9234237942')
   >>> result = myhex & hex2
   >>> result
   78184067072L

If you want to convert back to hex, go:

   >>> hex(result)
   '0x1234223000L'

hex returns a string, which you can eval into a
long again if need be.

Shifting left and right is done on the longs, using
the << and >> operators.

Kirby