Feedback for n3704 - Clean up frexp, ldexp, and scalbn prototypes

[Alejandro Colomar <une+c@alejandro-colomar.es>]

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Hi!


I see n3704 attempts to fix the issues reported by Vincent; that's good.
<https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3704.pdf>

However, the paper renames the pointer to 'p', which doesn't seem to
have good mnemonics nor relate to what it is.  'p' seems to just be
for 'pointer'?  We can and should do better.

I think alx-0051 was better, in using a parameter name that relates to
what the parameter means: 'e' for exponent.  Names matter.

I think we should discuss the name in the meeting.  Also, I think n3704
should have included a rationaly for the name; especially, when a better
name has been proposed, and for some reason the proposal decided to use
a different one; that should certainly have been discussed.

I think we can discuss the name in meeting without having to officially
present alx-0051 with an N-document number.  Please let me know if I
should formally present alx-0051 for the next meeting.


Have a lovely night!
Alex

On Tue, Jul 15, 2025 at 12:24:29AM +0200, Alejandro Colomar wrote:
> Hi!
> 
> Vincent reported this issue to me in the Linux man-pages mailing list
> (as the manual pages also had the same issue, so he reported the issue
> in both the manual pages and the ISO C standard).  I think this can be
> fixed editorially without going through an official N-document.  Please
> find the proposal below.
> 
> 
> Have a lovely night!
> Alex
> 
> ---
> Name
> 	alx-0051r0 - don't misuse reserved identifier 'exp'
> 
> Category
> 	Editorial.
> 
> Author
> 	Reported-by: Vincent Lefevre <vincent@vinc17.net>
> 	Signed-off-by: Alejandro Colomar <alx@kernel.org>
> 
> History
> 	<https://www.alejandro-colomar.es/src/alx/alx/wg14/alx-0051.git/>
> 
> 	r0 (2025-07-15):
> 	-  Initial draft.
> 
> Rationale
> 	Since 'exp' is a library function, it is a reserved identifier,
> 	which should not be used as a variable / parameter name.
> 
> 	7.1.3p1 says
> 
> 		All potentially reserved identifiers (...) that are
> 		provided by an implementation with an external
> 		definition are reserved for any use.
> 
> Proposed wording
> 	Based on N3550.
> 
>     7.17.7.5  The atomic_compare_exchange generic functions
> 	@@ Description, p7 EXAMPLE
> 	-	exp = atomic_load(&cur);
> 	+	e = atomic_load(&cur);
> 		do {
> 	-		des = function(exp);
> 	+		des = function(e);
> 	-	} while (!atomic_compare_exchange_weak(&cur, &exp, des));
> 	+	} while (!atomic_compare_exchange_weak(&cur, &e, des));
> 
>     B.11  Mathematics <math.h>
> 	@@
> 	...
> 	-_FloatN frexpfN(_FloatN value, int *exp);
> 	-_FloatNx frexpfNx(_FloatNx value, int *exp);
> 	-_DecimalN frexpdN(_DecimalN value, int *exp);
> 	-_DecimalNx frexpdNx(_DecimalNx value, int *exp);
> 	+_FloatN frexpfN(_FloatN value, int *e);
> 	+_FloatNx frexpfNx(_FloatNx value, int *e);
> 	+_DecimalN frexpdN(_DecimalN value, int *e);
> 	+_DecimalNx frexpdNx(_DecimalNx value, int *e);
> 	...
> 
> 	@@
> 	...
> 	-_FloatN ldexpfN(_FloatN value, int *exp);
> 	-_FloatNx ldexpfNx(_FloatNx value, int *exp);
> 	-_DecimalN ldexpdN(_DecimalN value, int *exp);
> 	-_DecimalNx ldexpdNx(_DecimalNx value, int *exp);
> 	+_FloatN ldexpfN(_FloatN value, int *e);
> 	+_FloatNx ldexpfNx(_FloatNx value, int *e);
> 	+_DecimalN ldexpdN(_DecimalN value, int *e);
> 	+_DecimalNx ldexpdNx(_DecimalNx value, int *e);
> 	...
> 
> 	@@
> 	...
> 	-_FloatN scalbnfN(_FloatN value, int *exp);
> 	-_FloatNx scalbnfNx(_FloatNx value, int *exp);
> 	-_DecimalN scalbndN(_DecimalN value, int *exp);
> 	-_DecimalNx scalbndNx(_DecimalNx value, int *exp);
> 	+_FloatN scalbnfN(_FloatN value, int *e);
> 	+_FloatNx scalbnfNx(_FloatNx value, int *e);
> 	+_DecimalN scalbndN(_DecimalN value, int *e);
> 	+_DecimalNx scalbndNx(_DecimalNx value, int *e);
> 	-_FloatN scalblnfN(_FloatN value, int *exp);
> 	-_FloatNx scalblnfNx(_FloatNx value, int *exp);
> 	-_DecimalN scalblndN(_DecimalN value, int *exp);
> 	-_DecimalNx scalblndNx(_DecimalNx value, int *exp);
> 	+_FloatN scalblnfN(_FloatN value, int *e);
> 	+_FloatNx scalblnfNx(_FloatNx value, int *e);
> 	+_DecimalN scalblndN(_DecimalN value, int *e);
> 	+_DecimalNx scalblndNx(_DecimalNx value, int *e);
> 	...
> 
>     F.10.4.9  The ldexp functions
> 	@@ p1
> 	 On a binary system,
> 	-ldexp(x, exp)
> 	+ldexp(x, e)
> 	 is equivalent to
> 	-scalbn(x, exp).
> 	+scalbn(x, e).
> 
> 	## And remove bold from 'exp' in the paragraph above.  This is
> 	## probably present due to exp being considered as a reserved
> 	## identifier by some script, which is part of the consequences
> 	## of undefined behavior: UB might format your standard!  :)
> 
>     H.11.3  Functions
> 	@@ 7.12.7  Exponential and logarithmic functions
> 	## Apply same changes as in B.11 (see above).
> 
> 	@@ F.10.14  Payload functions, p2
> 	...
> 	 the exponent is an integral power of 2 and,
> 	 when applicable,
> 	-value equals x × 2*exp.
> 	+value equals x × 2*e.
> 
> -- 
> <https://www.alejandro-colomar.es/>



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