[erlang-questions] map over bitstring

rgowka1 <>
Wed Oct 27 20:24:58 CEST 2010


Hi -

How can I convert a bitstring that has only characters $1 and $0 into a binary.

<<0,1,0,0,1,0,0,1,0>> to << 2#0100100100 >> to << 292 >>

something similar to io_lib:fread("~2u", [$0,$1,$0,$0,$1,$0,$0,$1,$0])
but that works on bitstring instead of string.

thanks.

On Mon, Oct 25, 2010 at 6:23 AM, Morten Krogh <> wrote:
> Kostis,
>
> I followed your suggestion and compiled it to native code with erlc +native
> zip2.erl, which improves the runtime for
> both methods.
>
> The run times are, for a 100 MB binary, and the map function X -> X + 1 hard
> coded into the module and into the map method itself (which is not quite
> realistic):
>
> Not native:
>
> comprehension :     10 s
> my own bit syntax function : 14s
>
> native:
>
> comprehension: 3.7 s
> my own bit syntax function: 6 s
>
> So, yes native is an improvement!
>
> Morten.
>
>
>
> On 10/25/10 11:30 AM, Kostis Sagonas wrote:
>>
>> Morten Krogh wrote:
>>>
>>> Sorry, in my recent reply to Tony I tested the comprehension on the
>>> constant ><<"B"">>.
>>>
>>> Putting everything in the module and comparing the same mapped function
>>> ,f , the result is that the comprehension is 30% faster than my matching
>>> based map function.
>>
>> Morten,
>>
>> You may also want to try compiling the file to native code and report
>> whether or how this improves/changes the results.
>>
>> Cheers,
>> Kostis
>
>
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