Re: How to read 12 bits from a stream ?
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- Subject: [mg131885] Re: How to read 12 bits from a stream ?
- From: roby <roby.nowak at gmail.com>
- Date: Wed, 23 Oct 2013 23:45:54 -0400 (EDT)
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Am Dienstag, 22. Oktober 2013 06:53:24 UTC+2 schrieb J=E1nos L=F6bb:
> Hi,
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> I am trying to read a mixed file - binary and text - with OpenRead and Read and BinaryRead, but I am not seeing a seek option, that is to move the pointer inside the file where I want it to be. Of course I can do a read in a loop with a counter, but I hoped there is a better way to do it.
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> The file is 16.1MB, the first 912 elements are characters and binary mixed, followed by 16MB binary section. The binary in this second section is packed in the way that 2 times 12 bits of little endian value is packed into 3 bytes. I need to unpack them and put them into big endian order. I am not seeing how can I read 12 bits at once with BinaryRead, it is aligned at the multiples of 8 bits.
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> Any good tip ?
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> Thanks ahead,
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> J=E1nos
Hi Janos,
SetStreamPosition[stream, pos]
does the positioning miracle
BinaryRead[stream, "UnsignedInteger24",ByteOrdering -> -1]
lets you read 24 bits
BinaryRead[stream, "UnsignedInteger24",ByteOrdering -> -1]//{BitAnd[#, 2^12- 1], BitAnd[BitShiftRight[#, 12], 2^12 - 1]} &
gets you two 12bit numbers.
Regards Robert