[erlang-questions] Arithmetic expressions [WAS: Re: Binaries problem]
Wed May 2 22:52:19 CEST 2007
Jim Thompson wrote:
> Francesco Pierfederici wrote:
> > > Hi,
> > >
> > > I have encountered a problem with handling binaries and I do not know
> > > what the cause might be. In a nutshell, I seem to be unable to
> > > assemble binaries larger than 2097149 bytes:
> > >
> Per Gustafsson wrote:
>> I think that the problem you are running in to is that you are creating
>> an integer that is too big for the erlang runtime system. I'm not sure
>> exactly where this limit is but it should be in the order of what you
>> are creating.
> jim@REDACTED:~$ erl
> Erlang (BEAM) emulator version 5.5.2 [source] [async-threads:0]
> Eshell V5.5.2 (abort with ^G)
> 1> round(math:pow(2,21))-3.
Unrelated to the topic, but we had weird cases where the HiPE compiler
was crashing when compiling binaries in R11B-3. They were all related
to use of an expression that was similar to the one Jim is using:
round(math:pow(2,N)) - K.
In examining the problem, we realized that this was a very stupid way of
denoting this quantity. We solved the problem (in R11B-4) by adopting a
much better (and significantly faster) way of writing the same
expression in Erlang:
(2 bsl (N-1)) - K
I suspect this "round + math:pow(2)" combination is not so uncommon
after all ... although there is really no reason to use it.
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