Re: Tiger Decoding problem
Re: Tiger Decoding problem
- Subject: Re: Tiger Decoding problem
- From: Nicholas Crosbie <email@hidden>
- Date: Tue, 31 May 2005 12:55:48 +1000 (EST)
Thanks again Dustin, but see my comment below viz.
big endian data.
Nick
--- Dustin Voss <email@hidden> wrote:
> On 30 May 2005, at 6:54 PM, Nicholas Crosbie wrote:
>
> > Thanks Dustin. I think now I'll be going places.
> But
> > before
> > I go away and play with this, note that my data
> was
> > produced for
> > a mac and is in the form of "\$BYTEORD\4,3,2,1"
> .
>
> I have no idea what that notation means...
Actually, according to the data file specification,
this
implies the data is written with the most important
bit first, ie. big endian.
> > Also, the data I'm trying to read is "a 10-bit
> > number.....stored in 16-bit space.......leaving 6
> > empty bits"
>
> ...but this means that it is a 2-byte number less
> than 1024. I
> correctly guessed little-endian.
>
> > Does this mean that I need to include a bitmask?
> Do
> > you know
> > how to do that?
>
> You do not need to use a bit-mask here. A bit-mask
> simply removes
> certain bits from consideration by setting them to
> 0. In your case,
> the irrelevant bits are already "empty," meaning 0.
> But...
>
> If you ever do need to construct a bit-mask, you
> simply have a 1 for
> every relevant bit, and a 0 for every irrelevant
> bit. The bit-mask
> for 10 of 16 bits like in your file is:
>
> 0b0000001111111111 or 0x03FF
>
> You apply the bit-mask, setting the irrelevant bits
> to 0, with the &
> operator:
>
> #define BITMASK 0x03ff
> maskedValue = rawValue & BITMASK;
>
> You alter the relevant bits of a mask like this:
>
> newValue = rawValue & ~BITMASK;
> newValue |= /*a bit to set*/ | /*another bit to
> set*/;
>
> If you know your Boolean logic, you can see how this
> works.
>
>
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