On Jul 5, 2011, at 12:26 AM, Nicolas Cellier wrote: > 2011/7/5 Douglas McPherson <[email protected]>: >> Two's complement is a platform representation of integers not (necessarily) >> a smalltalk one. The concept of negative numbers has nothing to do with the >> radix a number is expressed in. >> >> There are convenient extensions to the ByteArray protocol added by FFI which >> allow easy conversion though. I don't have time this second to list them, >> but will do so in a few hours. >> >> > > That's true, but the internal implementation leaks out the bitAnd: > bitOr: and other bit operations...
what do you mean by this sentence? That using bitAnd: we can get an idea of the implementation? exactly :) > > Nicolas > >> >> On Jul 4, 2011, at 15:14 , Stéphane Ducasse wrote: >> >>> Sven do your code work with Smalltalk smallInteger? >>> Because I think that in that case you should have 31 bits? >>> >>> >>>>> 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 >>>> >>>> >>>> >>> >>> >> >> >> >
