I'm sure I'm missing something obvious, but I'd like to be able to convert integers to and from byte arrays in native machine byte ordering, without resorting to a new primitive.
1) Does Squeak know the byte order convention of the hardware it's running on? I can't find any method to query for this.
2) Class ByteArray knows how to convert itself into integers, given that you can tell it the answer to question 1. Is there any existing method for converting an integer into a four byte array?
Thanks.
David:
The way to do this is to leverage off the fact that BitBlt can copy into either a ByteArray or a Bitmap object. (See the method "hackBits:".) What you do is to make a one-word Form with a byte array as its bits, then set the first byte to, say, 1. You BitBlt it into another one-word Form with a real Bitmap as its bits and read out the word using "bits at: 1". You'll either get 1 or 2^24, depending on the native byte ordering of the underlying architecture.
Warning: BitBlt may soon change so that this trick no longer works. But there will probably be a similar trick that you can use.
Hope this helps.
-- John
is pretty easy to do if you realize that
I'm sure I'm missing something obvious, but I'd like to be able to convert integers to and from byte arrays in native machine byte ordering, without resorting to a new primitive.
- Does Squeak know the byte order convention of the hardware it's running
on? I can't find any method to query for this.
- Class ByteArray knows how to convert itself into integers, given that
you can tell it the answer to question 1. Is there any existing method for converting an integer into a four byte array?
Thanks.
On Sun, Oct 31, 1999 at 11:37:59AM -0500, David T. Lewis wrote:
I'm sure I'm missing something obvious, but I'd like to be able to convert integers to and from byte arrays in native machine byte ordering, without resorting to a new primitive.
- Does Squeak know the byte order convention of the hardware it's running
on? I can't find any method to query for this.
- Class ByteArray knows how to convert itself into integers, given that
you can tell it the answer to question 1. Is there any existing method for converting an integer into a four byte array?
For what it's worth, here is what I ended up using, based on several suggestions and tips. Duly noted that code which relies on byte ordering, word size, and so forth is a Very Bad Idea and is almost certainly unnecessary.
isLittleEndian "Answer true if the machine on which we are executing uses little endian byte order conventions."
^ ((ReadStream on: (ByteArray newFrom: #(0 0 4 210))) nextNumber: 4) == 1234
isBigEndian "Answer true if the machine on which we are executing uses big endian byte order conventions."
^ self isLittleEndian not
byteArrayFromInteger: anInteger "Convert anInteger into a four byte ByteArray in machine dependent byte ordering. Assumes 32 bit integer word size for this machine."
| b | b _ ByteArray new: 4. self isBigEndian ifTrue: [(WriteStream on: b) nextNumber: 4 put: anInteger] ifFalse: [(WriteStream on: b) nextLitteEndianNumber: 4 put: anInteger]. ^ b
integerFromByteArray: anArrayOfFourBytes "Convert a four byte ByteArray in machine dependent byte ordering to an integer. Assumes 32 bit integer word size for this machine."
^ anArrayOfFourBytes longAt: 1 bigEndian: self isBigEndian
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David T. Lewis -
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