[boost] two_pi or pi_twice?

From: Paul A. Bristow (boost_at_[hidden])
Date: 2002-10-23 11:12:25

I had previously produced a naming scheme for constants, but this is now
in conflict with the naming scheme using by the recently introduced Interval
Library.

So I would appreciate views (I have a zero expectation of any consensus!!) on
the relative attractiveness of two schemes:

Previous Meth Constant Naming Convention

In general, a Standard Library C++ style is used, favouring longer and easier to
read names over ease of typing, and all lower case and underscore _ as
separator. Of course, names cannot start with a digit, so words, like two and
half, are used instead. C99 names are used where appropriate, but names are not
in all capitals as used in many C programs using the rationale that these names
are variable names and not macro or #define names.

Some examples, and a rationale for them, should make this clearer than an
attempt to write a formal specification. (Of course there are always problems
with more complex constants where brackets would be used).

pi      // Prefer lower case only - use uppercase only for class_names and MACRO
constants.
ln_pi   // _ as separator clearer than lnpi, even if longer and hard to type.
sqrt_2  // shorter than sqrt_two and clearer than sqrt2.
        // sqrt is commonly used and much shorter than square_root_2.
cbrt_2  // ugly, but is C99 name.
ten     // can’t be decimal digits like 10 so use a word instead.
third   // shorter than one_div_three.
one_div_sqrt_2 // one_div rather than reciprocal – short but clear.
        // _div rather than _on or _upon.
half_pi // rather than pi_div_2.
pi_sqr  // pi_squared is rather long.
two_pow_three_halves // two_pow_three_div_two is ambiguous.
minus_ln_ln_2 // can't start with - sign so use word "minus".

Or should it be the Interval library convention that puts the constant name
first - an obvious plus point when making ordered lists - all the pi constants
will come together.

pi_half  // should be halved?
pi_quarter // quarter_pi is nicer?
pi_twice // Not as clear as two_pi?
pi_thrice // Hmmm
pi_four_thirds //  or four_thirds_pi
pi_four_times // four_pi is much better.
pi_times_four // four_pi is better?
pi_ln    // Not so clear as ln_pi?
pi_log10 // base 10
pi_sqrt  //
pi_sqr   // as above scheme.
pi_cbrt  // ugly but C99
pi_reciprocal // because can't have one_div_pi

two // fine.
two_sqrt // sqrt_2 or sqrt_two are much clearer.
five_cbrt // Hmmm.

one_minus // Nasty compared to minus_one or minus_1
half_minus //

And while I am seeking views on names, do the following seem sensible:

Explicit typed names

pi_f // float
pi_d // double
pi_l // long double or pi_l ??
// Potential ambiguity of long int and long double here!
// C standard ISO 9899:1999 (a.k.a. C99) choses _l for long double
pi_i // integer
pi_li // long integer // or pi_l conflists with C99 ??

Interval limit static const constant variable names - add _l and _u

pi // nearest to pi (usually == either upper and/or lower interval limit)
pi_l // pi interval lower limit
pi_u // pi interval upper limit
pi_f_l // pi float lower limit
pi_l_l // pi long double lower limit
pi_l_u // pi long double upper limit

Are there any other precedents or good examples - before I expose Math Cosntants
to another Formal Review.  I think consistency in naming is surprisingly
important.

Thank you.

Paul

PS Has anyone devised or used a 32, 64 or 128 bit signed or unsigned fractional
type (in C++) - like a floating point type with all significand and without
exponent.

Paul A Bristow, Prizet Farmhouse, Kendal, Cumbria, LA8 8AB  UK
[phone]   Mobile [phone]
Mobile mailto:pabristow_at_[hidden]
mailto:pbristow_at_[hidden]