[Cfp-interest] quantexp (or .) for Part 3

[James W Thomas]

On May 28, 2013, at 1:25 AM, Mike Cowlishaw <mfc at speleotrove.com> wrote:

> 
>> At the May CFP teleconference we decided for Part 3 to add 
>> quantum-exponent functions that return in a decimal type and 
>> for Part 2 to retain its current quantexpd[32|64|128] 
>> functions that return int. What to name the new functions?
>> 
>> Following the naming pattern of using a prefix to reflect the 
>> return type, we might have dquantexp or decquantexp. In other 
>> <math.h> cases, this prefix convention is used to indicate 
>> integer type returns (ilogb, lrint, etc.), instead of the 
>> presumed floating type returns (logb, rint, etc.) for 
>> <math.h> functions. Ideally, we would have used iquantexp for 
>> the ones returning int and quantexp for the ones return 
>> decimal types. qexp won't work because it's used as the name 
>> of a function in statistics.
> 
> Perhaps it _should_ be named iquantexp: implementations that already use the TR
> names (are there any?) could provide backwards compatibility by means of a macro
> or wrapper function.
> 
>> A different approach. We might define a function that returns 
>> the quantum as defined in IEC 60559: the value of a unit in 
>> the last position of the significand (i.e., 10^q where q is 
>> the quantum exponent). We could call the function quantum. 
>> The quantum exponent could be obtained by, for example, 
>> logbdN(quantumdN(arg)). Would a quantum function be more or 
>> less useful than the quantexp function?
> 
> I have been surprised how useful the quantum function is; in particular its
> result displays and formats well alongside associated data, so it is easy to
> handle and (for common quanta) is readily understood (e.g., 0.01 for cents).

Mike, is the quantum function you've used provided by some implementation, or is it something you implemented as a user?

-Jim 

> 
> By there way, there's no reason not to provide it for binary types: woodworkers
> in the USA (for example) commonly work with inches to some binary quantum (e.g.,
> 1/32nds).
> 
> Mike
>