On Mon, Aug 20, 2012 at 1:29 PM, Dennis Lee Bieber
<wlfr...@ix.netcom.com> wrote:
> On Mon, 20 Aug 2012 16:52:42 +0200, Jean-Michel Pichavant
> <jeanmic...@sequans.com> declaimed the following in
> gmane.comp.python.general:
>
>> note that the builtin bin function is not available with python ver < 2.6
>>
>> def Denary2Binary(n):
>> '''convert denary integer n to binary string bStr'''
>> bStr = ''
>> if n < 0: raise ValueError, "must be a positive integer"
>> if n == 0: return '0'
>> while n > 0:
>> bStr = str(n % 2) + bStr
>> n = n >> 1
>> return bStr
>>
>> JM
>>
>> (not my function but I can't remember who I stole from)
>
> I think I typically have done this by going through a hex
> representation.
>
> H2B_Lookup = { "0" : "0000", "1" : "0001",
> "2" : "0010", "3" : "0011",
> "4" : "0100", "5" : "0101",
> "6" : "0110", "7" : "0111",
> "8" : "1000", "9" : "1001",
> "A" : "1010", "B" : "1011",
> "C" : "1100", "D" : "1101",
> "D" : "1110", "F" : "1111" }
>
> def I2B(i):
> sgn = " "
> if i < 0:
> sgn = "-"
> i = -i
> h = ("%X" % i)
> return sgn + "".join([H2B_Lookup[c] for c in h])
>
>>>> from i2b import I2B
>>>> I2B(10)
> ' 1010'
>>>> I2B(1238)
> ' 010011100110'
>>>> I2B(-6)
> '-0110'
>>>>
> --
> Wulfraed Dennis Lee Bieber AF6VN
> wlfr...@ix.netcom.com HTTP://wlfraed.home.netcom.com/
>
> --
> http://mail.python.org/mailman/listinfo/python-list
This may be moving off topic, but since you encode -6 as -0110 I
thought I'd chime in on 'two's complement'
with binary number, you can represent 0 to 255 in a byte, or you can
represent numbers from 127 to -128. To get the negative you
complement each bit (0s to 1s, 1s to 0s), then add one to the result.
So:
3 --> 00000011
~3 -> 111111100
add 1 1
result 111111101
The nice thing about this representation is that arithmetic works just
fine with a mixture of negative and positive numbers.
eg 8 + (-3) ----> 00001000
111111101
gives: 00000101
which is 5!
--
Joel Goldstick
--
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