On 14 April 2024 16:55:43 BST, Saki Takamachi <s...@sakiot.com> wrote:
>Hi Gina,
>
>> Hello internals,
>>
>> While reviewing the PR for the "Adding bcround, bcfloor and bcceil to
>> BCMath" RFC [1] with the different rounding modes,
>> I was made aware of the unfortunate wrong terminology usage of
>> PHP_ROUND_HALF_UP and PHP_ROUND_HALF_DOWN.
>>
>> Indeed, PHP_ROUND_HALF_UP is implemented as "rounding half away from zero"
>> and not "rounding half up" (which is also called rounding toward positive
>> infinity).
>> The behaviour for positive numbers is the same, however for negative numbers
>> the rounding *is* different.
>> In the same vein, PHP_ROUND_HALD_DOWN is implemented as "rounding half
>> toward zero" and not "rounding half down" (/round half toward negative
>> infinity).
>>
>> Taking -1.5 as our number:
>> - Rounding half-up: -1
>> - Rounding half away from zero: -2
>> - Rounding half-down: -2
>> - Rounding half towards zero: -1
>>
>> For a detailed explanation about rounding, the Wikipedia page is of great
>> use. [2]
>> And the following rounding calculator on Calculator Soup is useful to check
>> the differences and behaviour of different rounding modes. [3]
>>
>> It should be noted that PHP is in good company about being wrong about those
>> two rounding modes, Java, Python, and Ruby (and probably others) are also
>> wrong in this regard.
>>
>> Considering that PHP 8.4 is also adding new rounding modes via the "Add 4
>> new rounding modes to round() function" RFC [4] attempting to solve this
>> issue in this next version of PHP seems like a good idea.
>> In my discussions with Saki about this issue, it seems that her and Tim have
>> thought about creating a new enum for rounding modes, looking something like
>> this:
>>
>> enum RoundingMode {
>> case HalfAwayFromZero;
>> case HalfTowardsZero;
>> case HalfEven;
>> case HalfOdd;
>> case TowardsZero;
>> case AwayFromZero;
>> case NegativeInfinity; // or case Floor;
>> case PositiveInfinity; // or case Ceiling;
>> }
>>
>> and change the signature of round from:
>> round(int|float $num, int $precision = 0, int $mode = PHP_ROUND_HALF_UP):
>> float
>> to
>> round(int|float $num, int $precision = 0, RoundingMode $mode =
>> RoundingMode::HalfAwayFromZero): float
>>
>> and changing the definition of the existing constants to effectively be:
>> define('PHP_ROUND_HALF_UP', RoundingMode::HalfAwayFromZero);
>> define('PHP_ROUND_HALF_DOWN', RoundingMode::HalfTowardsZero);
>> define('PHP_ROUND_HALF_EVEN', RoundingMode::HalfEven);
>> define('PHP_ROUND_HALF_ODD', RoundingMode::HalfOdd);
>>
>> This should not cause any BC breaks, while allowing us to potentially
>> implement the half up/down rounding modes properly, and deprecate the
>> existing rounding constants in the future to get rid of the confusing names.
>>
>> I wanted to know if anyone has any object to introducing this new enum and
>> signature change.
>> The only thing I could think of is if this enum should be in a new Maths (or
>> Math or just Mathematics to not need to deal with regional difference in the
>> short spelling of "Mathematics") namespace.
>>
>> Best regards,
>>
>> Gina P. Banyard
>>
>> [1] https://wiki.php.net/rfc/adding_bcround_bcfloor_bcceil_to_bcmath
>> [2] https://en.wikipedia.org/wiki/Rounding
>> [3]
>> https://www.calculatorsoup.com/calculators/math/rounding-methods-calculator.php
>> [4] https://wiki.php.net/rfc/new_rounding_modes_to_round_function
>
>In my discussions with Tim, I want to make it clear that all ideas derived are
>Tim's. :)
>
>Now, of course I agree with this, and agree with using namespaces. However, if
>didn't use namespaces, that's fine by me. For reference, we found
>approximately 100 pieces of code using the namespace `Math` on Github Code
>Search. There are only a few cases for `Maths` and 0 for `Mathematics`.
>
>Regards,
>
>Saki
Math is American English spelling, Maths/Mathematics the British English one.
As we also have color (and not the "correct" colour), going with the American
spelling seems better.
But I would query whether we actually need it in a namespace.
cheers
Derick
