Path: csiph.com!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c++
Subject: Re: C++20 concepts rocks
Date: Fri, 04 Feb 2022 23:53:04 -0800
Organization: A noiseless patient Spider
Lines: 65
Message-ID: <865yptlpgf.fsf@linuxsc.com>
References: <stj7m4$bim$1@dont-email.me> <stjd0m$1380$1@gioia.aioe.org> <stjdbe$7th$1@dont-email.me> <87k0easj5d.fsf@bsb.me.uk>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Injection-Info: reader02.eternal-september.org; posting-host="fd296145b453fec571e4c44d6840aea3"; logging-data="758"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX19UrRH1qw2XRrmPAwPCOHk9Mj6Am2LY6gM="
User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.4 (gnu/linux)
Cancel-Lock: sha1:Ru/ebPqPGzlMgBGAzvGJ+P4fQTQ= sha1:vpdXotFzzrULwLipyaWnmrdThLM=
Xref: csiph.com comp.lang.c++:82908

Ben Bacarisse <ben.usenet@bsb.me.uk> writes:

> Bonita Montero <Bonita.Montero@gmail.com> writes:
>
>> Am 04.02.2022 um 15:25 schrieb Muttley@dastardlyhq.com:
>>
>>> On Fri, 4 Feb 2022 13:54:27 +0100
>>> Bonita Montero <Bonita.Montero@gmail.com> wrote:
>>>
>>>> I've just written a small routine:
>>>>
>>>> [.. some c++ code ..]
>>>
>>> Thats nice.  Personally I'd just use printf().
>>
>> You can't do what I did with (s)printf().
>
> template<typename StringType>
> requires is_same_v<StringType,
>                    basic_string<typename StringType::value_type,
>                                 typename StringType::traits_type,
>                                 typename StringType::allocator_type>>
> StringType formatClockCycles(uint64_t clockCycles)
> {
>    char result[28], *ep = (&result)[1];
>    do {
>       sprintf(ep - 4, "%03lu", clockCycles % 1000);
>       if (ep != (&result)[1]) ep[-1] = '.';
>       ep -= 4;
>    } while (clockCycles /= 1000);
>    while (*ep == '0' && ep[1]) ep++;
>    return ep;
> }
>
> (the appropriate comment on the 28 is left as an exercise to the reader!)

Most of the work can be done using only a single call to sprintf().
(Disclaimer:  not compiled.)


    template< typename StringType >
        requires
            is_same_v<
                StringType,
                basic_string<
                    typename StringType::value_type,
                    typename StringType::traits_type,
                    typename StringType::allocator_type
                >
            >
    StringType
    formatClockCycles( uint64_t clockCycles ){
        char result[ 27 ];
        int n = sprintf( result, "%" PRIu64, clockCycles );
        char *ep = (&result)[1];

        *--ep = 0;
        while(  n > 3  ){
            memmove( ep -= 3, &result[ n -= 3 ], 3 );
            *--ep = '.';
        }
        do  *--ep = result[ --n ];  while(  n > 0  );

        return  ep;
    }