[erlang-patches] new float_to_list/2

Björn-Egil Dahlberg <>
Fri Jan 11 14:53:53 CET 2013


On 2013-01-11 14:24, Serge Aleynikov wrote:
> While looking at this I see that the code in folder
> "erts/emulator/sys/vxworks" is present in maint but missing in the
> master branch.  Is this intentional?  If so, should I remove the part of
> the patch designed for vxworks?
Yes. Any and all vxworks support has been removed in R16 from OTP except 
for epmd, erl_interface and ic.

// Björn-Egil
>
> On 1/11/2013 3:52 AM, Fredrik wrote:
>> Hey,
>> Could you please rebase this on current 'master' branch?
>>
>> BR Fredrik Gustafsson
>> Erlang OTP Team
>> On 01/11/2013 04:06 AM, Serge Aleynikov wrote:
>>> I implemented Lukas's recommendations that were presenting an acceptance
>>> issue of the new function, so the current version of the patch does:
>>>
>>> 1. float_to_list/1 is backwards compatible.
>>> 2. float_to_list(X,[]) gives the same result as float_to_list(X).
>>> 3. float_to_list(X,[{decimals,N}]) uses the new fast implementation
>>> (with the optional compact option).
>>> 4. float_to_list(X,[{scientific,M}]) gives the same result as
>>> float_to_list(X) with the ability to control the number of decimals.
>>>
>>> The only item from Lucas's list that I left unchanged was the
>>> modification to erts/lib_src/common/erl_printf_format.c to take
>>> advantage of the speed improvement of the new implementation.  I am
>>> including a patch in this email that implements this logic, but I
>>> decided to leave the integration task to the OTP team since
>>> erl_printf_format.c is actually compiled into a liberts_internal.a
>>> library and I didn't want to introduce a dependency of it on other code
>>> - this should be decided by maintainers.
>>>
>>> The test cases of float_to_list/{1,2} have been updated.
>>>
>>> git fetch https://github.com/saleyn/otp/tree/float_to_list_2
>>>
>>> https://github.com/saleyn/otp/compare/maint...float_to_list_2
>>> https://github.com/saleyn/otp/compare/maint...float_to_list_2.patch
>>>
>>> Regards,
>>>
>>> Serge
>>>
>>> On 8/23/2012 5:10 AM, Lukas Larsson wrote:
>>>> Hi,
>>>>
>>>> I'll put it in the backlog and we'll see if it gets prioritized for R16B.
>>>>
>>>> As always if you (or someone else) wants make sure it gets in, the best
>>>> way to ensure that is to send an updated patch.
>>>>
>>>> Lukas
>>>>
>>>>
>>>> On 22/08/12 21:17, Serge Aleynikov wrote:
>>>>> I am certainly very happy to hear that you finally agreed to include
>>>>> this in the distribution.  The changes proposed below seem reasonable
>>>>> and simple.  Will the OTP team be able to modify my patch to implement
>>>>> them?
>>>>>
>>>>> On 8/22/2012 12:01 PM, Lukas Larsson wrote:
>>>>>> Hello Serge!
>>>>>>
>>>>>> I think we have finally agreed how we want this functionality to work.
>>>>>>
>>>>>> float_to_list/1 should be left as it is now for backwards compatibility.
>>>>>> float_to_list(1.0,[]) should give the same as float_to_list(1.0).
>>>>>> float_to_list(1.0,[{decimals,X}]) should use your faster implementation
>>>>>> (with the optional compact option).
>>>>>> float_to_list(1.0,[{scientific,Y}]) should give the same as
>>>>>> float_to_list(1.0) if Y is 20.
>>>>>>
>>>>>> We would also like the string rendering part of sys_double_to_chars_fast
>>>>>> to be put into erts/lib_src/common/erl_printf_format.c:fmt_double. This
>>>>>> way other parts of the vm which print floats will benefit from your
>>>>>> changes!
>>>>>>
>>>>>> I hope our indecisiveness have not caused you to shy away from taking
>>>>>> this feature into Erlang/OTP. If you have any further questions or
>>>>>> ponderings just let me know.
>>>>>>
>>>>>> Lukas
>>>>>>
>>>>>> On 18/07/12 20:47, Serge Aleynikov wrote:
>>>>>>> On 7/18/2012 5:18 AM, Lukas Larsson wrote:
>>>>>>>> However, I would also like the fast functionality to be used by
>>>>>>>> float_to_list_1 as well, is possible to do this and stay backwards
>>>>>>>> compatible? Hopefully you just have to shift the comma and add e+XX at
>>>>>>>> the end of the optimized case and call sys_double_to_chars for the
>>>>>>>> unoptimized.
>>>>>>> See my comments below regarding 'scientific' option.  Since
>>>>>>> float_to_list_2 is a new function I would think that you are
>>>>>>> questioning
>>>>>>> the issue of backward compatibility only in terms of converting
>>>>>>> float_to_list_1 to use float_to_list_2 implementation.  However, I
>>>>>>> think
>>>>>>> that this will have adverse performance tax on float_to_list_2, which
>>>>>>> will diminish the benefit.  It's been a while however, since I wrote
>>>>>>> that patch, perhaps there's a way to retrofit scientific notation
>>>>>>> without a performance penalty.
>>>>>>>
>>>>>>> It's more than simple shifting of the comma, since there's also
>>>>>>> rounding
>>>>>>> involved.
>>>>>>>
>>>>>>> This case is easy:
>>>>>>>
>>>>>>> 4> float_to_list(1.01234).
>>>>>>> "1.01234000000000001762e+00"
>>>>>>> 5> float_to_list(1.01234, [{decimals, 20}]).
>>>>>>> "1.01234000000000001762"
>>>>>>>
>>>>>>> This case is a bit more complex (illustration of rounding impact):
>>>>>>>
>>>>>>> 7> float_to_list(10123412345.0123451234).
>>>>>>> "1.01234123450123443604e+10"
>>>>>>> 8> float_to_list(10123412345.0123451234, [{decimals, 20}]).
>>>>>>> "10123412345.01234436035156250000"
>>>>>>>
>>>>>>>> Also float_to_list(1.0) should return the same thing as
>>>>>>>> float_to_list(1.0,[]), otherwise the API will be inconsistent with how
>>>>>>>> other such APIs work.
>>>>>>> Actually if you trace this subject back there was another request that
>>>>>>> the default number of decimals is chosen to be consistent with what
>>>>>>> printf() does, so I changed the implementation to accommodate that
>>>>>>> request:
>>>>>>>
>>>>>>> Eshell V5.9  (abort with ^G)
>>>>>>> 1> float_to_list(1.0, []).
>>>>>>> "1.000000"
>>>>>>>
>>>>>>> Which is different from the default of float_to_list/1:
>>>>>>>
>>>>>>> 2> float_to_list(1.0).
>>>>>>> "1.00000000000000000000e+00"
>>>>>>>
>>>>>>> Maybe one could introduce a 'scientific' option to float_to_list/2, to
>>>>>>> use the float_to_list/1 implementation?
>>>>>>>
>>>>>>> Serge
>>>>>>>
>>>>>>>> On 24/05/12 16:02, Serge Aleynikov wrote:
>>>>>>>>> Henrik,
>>>>>>>>>
>>>>>>>>> Fetch:    git fetch
>>>>>>>>> https://github.com/saleyn/otp/tree/float_to_list_2
>>>>>>>>> Diff:    https://github.com/saleyn/otp/compare/float_to_list_2
>>>>>>>>>
>>>>>>>>> I added the definition for the new BIF to make the type checker
>>>>>>>>> happy:
>>>>>>>>> https://github.com/saleyn/otp/commit/f9ddbeda5426ca83cda03c06a9860220ea4a22c7
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Once you do the "otp_build tests", how do you execute all tests
>>>>>>>>> suites
>>>>>>>>> in $ERL_TOP or if possible only tests in a given SUITE?  I tried the
>>>>>>>>> following but all tests fail:
>>>>>>>>>
>>>>>>>>> [otp/erts/emulator/test]$ ../../../bin/erl -noshell -s
>>>>>>>>> test_server_ctrl
>>>>>>>>> run_test DIR "." -s erlang halt
>>>>>>>>>
>>>>>>>>> I did however run individual tests in bif_SUIT:types to make sure my
>>>>>>>>> patch didn't break anything.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Serge
>>>>>>>>>
>>>>>>>>> On 5/24/2012 5:17 AM, Henrik Nord wrote:
>>>>>>>>>> Hi again.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> This test is not passing: emulator/bif_SUIT:types
>>>>>>>>>>
>>>>>>>>>> No type information:
>>>>>>>>>>
>>>>>>>>>> [{erlang,float_to_list,2}]
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On 04/21/2012 07:19 AM, Serge Aleynikov wrote:
>>>>>>>>>>> git fetch https://github.com/saleyn/otp/tree/float_to_list_2
>>>>>>>>> _______________________________________________
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