[sac-user] print function alternatives?

Robert Bernecky bernecky at snakeisland.com
Mon Aug 9 16:07:15 CEST 2010

Such resource issues are usually negligible in real applications.
E.g., the time spent converting doubles to printable form
outweighs any time spent copying character arrays.

Consider real text-generation apps, such as creation
of web pages, formatting paychecks (Yes, I know they're
passe, but this sort of thing is common.), and the like.

The idea that formatting and output are more than
peripherally related is the sort of thing that gave
us ideas like I/O primitives that write to pseudo-devices,
so you could pseudo-read the result back in and tinker
it, sprintf(), and other miracles of computer engineering
that offer no elegance and end up making apps slower
to write, debug, and maintain than if the tasks of
formatting and I/O were clearly isolated from each other.

Divorcing formatting from I/O offers advantages to
the app writer. For example, the APEX compiler often
does things like this:

I can conceive of optimizations to speed up formatting
of arrays, but once you start introducing things like
This Result Must Be Generated One Row At A Time,
then things get messy. And then get worse.


Clemens Grelck wrote:
> I fully agree on the diversity of printing options. My only
> concern was to create a character array (!) explicitly, whose
> only purpose in life is to be printed. In one way or another
> this means copying one buffer into another and substantial
> organisational overhead as for instance the character array
> needs to be constructed incrementally, etc.
> I agree that from a software engineering point of view separating
> formatting issues from I/O issues is desirable.  From a resource
> point of view it is not.
> Still formatting is technically orthogonal from the I/O issue and
> all problems are the same. I thought about higher-order functions
> for providing entire print functions (or formatting functions) as
> arguments instead of format strings. But that is a long term issue
> and maybe not even worth it for the purpose of nice printing.
>  Clemens
> Robert Bernecky wrote:
>> Not necessarily so:
>> The conversion of a numeric array into a character
>> array (Strings can stay at home, please) offers several
>> advantages over code that includes output/input:
>> 1. In real applications, it becomes necessary to combine
>>    formatted arrays, as when creating reports:
>>       name             phone             salary
>>       Prof             (+44) 123 345     40 million pazoozas
>>       Lowly underling  (+1) 416 555 1212 20 pazoozas
>>    Each element of the report generally will need custom formatting;
>>    the use of a formatting function that produces a character matrix
>>    permits the individually formatted columns to be joined with
>>    catenation.
>> 2. Creation of certain sorts of files, such as CSV files, requires
>>    that formatted matrix elements be decorated (e.g., with commas
>>    separating them, with quotes around character fields, etc.), then
>>    have new-line characters appended, and the whole thing then
>>    ravelled to a vector, perhaps will trailing blanks removed,
>>    if you want to be tidy. This gets messy if you try to combine
>>    arbitrary formatting and I/O into the same construct.
>> I am not sure if higher-order functions help a lot here. For
>> example, the commas in CSV files are needed for all but the last
>> item in a row. Not sure what you have in mind here.
>> For real applications, you nearly always end up with custom
>> formatting functions anyway, except for the most trivial apps.
>> Bob
>> Clemens Grelck wrote:
>>> Much better. ;-)
>>> What might prove problematic in ArrayFormat is that, if I understand
>>> it correctly, an entire array is transformed into a string before that
>>> string (normally) is printed to some file descriptor and then removed
>>> again.
>>> I think this would be a good example for having higher-order functions,
>>> because what you in the end want to do is to map a print function to 
>>> each
>>> element of an array. And to have this print function user-controlled.
>>> A less comprehensive but then much easier and quicker to realise 
>>> solution
>>> could be to simply expose the format string in the user API. The
>>> implementation of the ArrayIO module already has this abstraction layer.
>>> At the moment, the exposed API function calls this one hard-wiring the
>>> format string. I think this could be realised within 15 minutes or so.
>>>  Clemens
>>> Robert Bernecky wrote:
>>>> Is this better?
>>>> 0.07
>>>> 0.07
>>>> 0.0700000000000000067
>>>> rbe at obelix:~> cat crud.sac
>>>> use Array:all;
>>>> use StdIO:all;
>>>> use ArrayFormat:all;
>>>> int main()
>>>> {
>>>>  x = 0.07;
>>>>  show(x);
>>>>  show(format(x));
>>>>  show(format(x,18));
>>>>  return(0);
>>>> }
>>>> Bob
>>>> Raphael 'kena' Poss wrote:
>>>>> Hi all,
>>>>> Op 2 aug 2010, om 18:45 heeft Robert Bernecky het volgende geschreven:
>>>>>> In particular, it still uses printf() [...]
>>>>>> My intent was to make it use a precise formatter, such
>>>>>> as that proposed in "Printing Floating-Point Numbers Quickly and 
>>>>>> Accurately", by Robert G. Burger and R. Kent Dybvig.
>>>>> For your information, many open-source Unices nowadays use the 
>>>>> gdtoa library by D. Gay from netlib: 
>>>>> http://www.netlib.org/fp/gdtoa.tgz
>>>>> This uses concepts and algorithms from
>>>>> T. J. Dekker, "A Floating-Point Technique for Extending the
>>>>> Available Precision", Numer. Math. 18 (1971), pp. 224-242
>>>>> and
>>>>> "How to Print Floating-Point Numbers Accurately" by
>>>>> Guy L. Steele, Jr. and Jon L. White [Proc. ACM SIGPLAN '90, pp. 
>>>>> 112-126].
>>>>> As far as precision goes, this is formally specified. I don't know 
>>>>> how it compares to the techniques in Burger & Dybvig, actually.
>>>>> As an option, is it possible to output floats in hexadecimal? This 
>>>>> should prevent rounding errors.
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