For positive integers, we have an infinite serie of 0 bits, but we don't care, we just don't print them. The problem with two complement is that you have an infinite serie of leading 1 bits... Otherwise, you can access the bit at any rank with bitAt: For example, you could use bitRepresentation ^(self digitLength * 8 + 1 to: 1 by: -1) collect: [:i | Character value: $0 charCode + (self bitAt: i)] as: String The first bit will aways be the sign with the + 1 trick. Nicolas 2011/7/4 Sven Van Caekenberghe <sven@beta9.be>:
On 04 Jul 2011, at 20:16, Stéphane Ducasse wrote:
I would like to see the two complement representation of numbers.
This is what I do, for reading/writing unsigned or two complement signed integer from/to byte streams.
Note that two complement is only defined for a specific number size, 8, 16, 32 bits.
unsignedToSigned: integer size: size     ^ integer < (2 raisedTo: size - 1)         ifTrue: [ integer ]         ifFalse: [ (self twoComplement: integer size: size) negated ]
signedToUnsigned: integer size: size     ^ integer negative         ifTrue: [ self twoComplement: integer size: size ]         ifFalse: [ integer ]
twoComplement: integer size: size     | mask |     mask := (2 raisedTo: size) - 1.     ^ mask bitAnd: ((integer abs bitXor: mask) + 1)
These are also very handy in this context (I believe I once submitted that as an issue):
integerFromByteArray: bytes     | integer |     integer := 0.     bytes withIndexDo: [ :each :index |         integer := integer + (each bitShift: (bytes size - index) * 8) ].     ^ integer
and Integer>>#asByteArrayOfSize:
Once you have a byte representation, you can render it as bits as well.
Sven