At Sat, 8 Oct 2011 17:41:35 +0100, "nicolas.o...@gmail.com" wrote: > I am trying to write a small implementation of Protocol Buffers ( > http://code.google.com/p/protobuf/ ) and I have difficulties > with bit manipulations, especially to transform a negative integer into a > series of bytes and back. > > I can not find an implementation of a non-arithmetic shift for fixnums, and > a way to specify which size of fixnum to construct.
There aren't different sizes of fixnums. When you want to convert an exact integer to bytes, then `integer->integer-bytes' lets you specify the size. There also isn't a logical shift operator, if I understand what you're after. If you work with positive integers, then `arithmetic-shift' (plus `bitwise-and'?) behaves like a logical shift. If you want logical-shift effects for finite 2's complement representations, then you probably don't really want to work on fixnum representations, which are 63 or 31 bits, but instead some power of 2 via bitwise operations like `bitwise-ior', `bitwise-and', and arithmetic shifts of negative numbers. Note also that `integer-bytes->integer' lets you say whether to interpret a set of bytes as unsigned or as 2's complement. > I can't also find an easy way to get the byte representation of flonums. `real->floating-point-bytes' _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
