[Cfp-interest 2896] Re: standardize printf %a/%A

[Mike Cowlishaw]

This would seem to be way down low on the C to-do list compared to having a
% indicator that allowed printing of int64_t and other 64-bit integers?

Mike 

> -----Original Message-----
> From: Cfp-interest [mailto:cfp-interest-bounces at oakapple.net] 
> On Behalf Of Paul Zimmermann
> Sent: 05 September 2023 18:56
> To: Steve (Swift) Canon
> Cc: cfp-interest at ucbtest.org
> Subject: [Cfp-interest 2892] Re: standardize printf %a/%A
> 
>        Hi Steve,
> 
> can you detail what the issue would be, for example for the 
> three conventions below?
> 
> 1) force the output (when non-zero) to begin with hexadecimal 
> digit '1'
>    (this makes it easy to grasp the magnitude of the number by looking
>    at the exponent)
> 2) for the output (when non-zero) to begin with an 
> hexadecimal digit >= '8'
>    (this minimizes the number of hexadecimal digits)
> 3) force the radix-2 exponent to be a multiple of 4
>    (this corresponds to a radix-16 output, with the exponent 
> converted into
>    redix 2)
> 
> Paul
> 
> > From: "Steve (Swift) Canon" <scanon at apple.com>
> > Date: Tue, 05 Sep 2023 13:20:26 -0400
> > Cc: cfp-interest at ucbtest.org
> > 
> > > On Sep 4, 2023, at 12:19 PM, Paul Zimmermann 
> <Paul.Zimmermann at inria.fr> wrote:
> > > 
> > >       Hi,
> > > 
> > > on the MPFR list there was some discussion about printf with 
> > > hexadecimal values (%a/%A):
> > > 
> > > https://sympa.inria.fr/sympa/arc/mpfr/2023-09/msg00004.html
> > > 
> > > It seems to me there is no convention in the C standard (both for 
> > > normal and subnormal values).
> > > Would it make sense to have one?
> > 
> > One consideration that makes it difficult to have a 
> sensible default is the mandatory promotion of float (and 
> other small types) to double in varargs functions like the 
> printf family. Unfortunately float and double don’t have the 
> same number of fractional bits mod 4, so many rules that one 
> might want to standardize will not hold when floats are used, 
> leading to a certain amount of surprise for users who don’t 
> understand the promotion rules.
> > 
> > That isn’t to say that it’s not worth doing, but a certain 
> amount of confusion is hard to avoid.
> > 
> > – Steve=