On Jan 16, 2008 2:41 PM, Dominic Steinitz
tlv_ bin = do tagValueVal <- getBits bin 5 tagConstructionVal <- getBits bin 1 tagTypeVal <- getBits bin 2
I'm sure I'm wrong but putting bits into [Bool] doesn't look very efficient. Of course, NewBinary didn't address what happened for n >= 8. Some possibilities are a) not allowing more than 8 b) returning [Word8] or c) (which I thought was where we'd go) a ByteString with some sort of padding.
BitGet is just an API RFC at the moment, so I'm just describing it here - not trying to justify it. In BitGet there's getAsWord[8|16|32|64] which take a number of bits ($n$) and returns the next $n$ bits in the bottom of a Word$x$. Thus, getAsWord8 is what you call getBits and, if you had a 48 bit number, you could use getAsWord64 and the bottom 48-bits of the resulting Word64 would be what you want. Equally, asking for more than $x$ bits when calling getAsWord$x$ is a mistake, however I don't check for it in the interest of speed. There are also get[Left|Right]ByteString which return the next $n$ bits in a ByteString of Word8's. The padding is either at the end of the last byte (left aligned) or at the beginning of the first byte (right aligned). If you did want a [Bool], you could use: bits <- sequence $ take n $ repeat getBit AGL -- Adam Langley agl@imperialviolet.org http://www.imperialviolet.org 650-283-9641