Efficient bitwise operations
Mon Jun 23 09:53:36 CEST 2003
Rudolph van Graan writes:
> I've had to write some bitwise operations yesterday, because I couldn't
> locate any bifs or operations that do the same:
Bengt has already mentioned bsl/bsr. Also, writing
> lroll1(<<B7:1,B6:1,B5:1,B4:1,B3:1,B2:1,B1:1,B0:1>>) ->
works, but is rather more verbose than
the latter also generates shorter BEAM assembly (try the 'S' option
when you compile).
> My question here has to do with the efficiency of the above code.
> Normally, I would have used a single assembly instruction to achieve the
> same result, but even though the code works, how efficient can it really
> be? Are there any obvious things I've missed in the documentation?
The pragmatic approach is: if you are thinking about "how many
assembly instructions does this bit manipulation turn into", then it's
time to move the code to something more suited to the task, such as C
or assembler. Either that, or stop thinking about it ;-)
There are several ways of interfacing C code to Erlang, each with its
own convenience/performance tradeoffs. They're described at
More information about the erlang-questions