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Groups > comp.lang.c > #150585
| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: How to div only once to get remainder and quotient? |
| Date | 2020-03-14 16:35 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <87fteaq4hc.fsf@bsb.me.uk> (permalink) |
| References | (4 earlier) <OeNaG.606942$%G5.570101@fx03.am4> <87blp0q9iz.fsf@bsb.me.uk> <z6TaG.617671$_R5.308687@fx19.am4> <87r1xvpv0b.fsf@bsb.me.uk> <u24bG.447711$QS6.357464@fx02.am4> |
Bart <bc@freeuk.com> writes:
> On 14/03/2020 01:47, Ben Bacarisse wrote:
<cut>
>> How about:
>>
>> static void str_to_bin_aux(uint64_t n, char *dest, int wd)
>> {
>> if (wd == 1)
>> *dest = "01"[n & 1];
>> else {
>> wd /= 2;
>> str_to_bin_aux(n, dest+wd, wd);
>> str_to_bin_aux(n >> wd, dest, wd);
>> }
>> }
>> char *str_to_bin(uint64_t n, char *dest)
>> {
>> enum { bits = sizeof n * CHAR_BIT };
>> str_to_bin_aux(n, dest, bits);
>> dest[bits] = 0;
>> return dest;
>> }
>>
>> :-)
>>
>> (By the way, names starting "str" and a lower case letter are reserved
>> for future use in string.h, hence my choice of "str_".)
>>
>
> Ah yes, the recursive solution. I felt obliged to put together my own,
> but it took ages to get it right and my confidence in it is not as
> great as with my iterative one. Not sure about UB either
> (eg. left-shifting by 0):
That's fine.
> void rstrbin(u64 a, char *dest, int bits) {
> if (bits) {
> if (a & (1LL<<(bits-1))) {
> *dest='1';
> } else {
> *dest='0';
> }
> rstrbin(a, dest+1, bits-1);
> } else {
> *dest=0;
> }
> }
>
> This is a one-function version, requiring an extra parameter, but I
> believe this is a useful addition to the spec (so you can display 8,
> 16, 32 or 64-bit wide numbers, or even 24 bits).
>
> Both recursive versions are slower than the iterative ones under gcc
> -O3, but mine seemed double the speed of yours using bits=64 (and will
> be faster with fewer bits). With bcc/tcc mine was 2.5 times as fast,
> when calling it 10M lines.
I wonder if gcc turned your one-sided recursion into a loop. My doubly
recursive version had a smiley for a reason!
--
Ben.
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How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-12 20:18 +0000
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-12 20:26 +0000
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-12 20:30 +0000
Re: How to div only once to get remainder and quotient? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-03-12 20:40 -0700
Re: How to div only once to get remainder and quotient? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-03-12 16:38 -0400
Re: How to div only once to get remainder and quotient? richard@cogsci.ed.ac.uk (Richard Tobin) - 2020-03-12 20:44 +0000
Re: How to div only once to get remainder and quotient? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-03-12 17:00 -0400
Re: How to div only once to get remainder and quotient? richard@cogsci.ed.ac.uk (Richard Tobin) - 2020-03-13 09:35 +0000
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-13 11:12 +0100
Re: How to div only once to get remainder and quotient? scott@slp53.sl.home (Scott Lurndal) - 2020-03-12 22:16 +0000
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-12 22:39 +0000
Re: How to div only once to get remainder and quotient? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-03-12 19:51 -0400
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-13 00:47 +0000
Re: How to div only once to get remainder and quotient? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-03-12 23:02 -0400
Re: How to div only once to get remainder and quotient? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-03-12 20:39 -0700
Re: How to div only once to get remainder and quotient? scott@slp53.sl.home (Scott Lurndal) - 2020-03-13 15:00 +0000
Re: How to div only once to get remainder and quotient? Spiros Bousbouras <spibou@gmail.com> - 2020-03-14 08:35 +0000
Re: How to div only once to get remainder and quotient? jak <nospam@please.ty> - 2020-03-12 21:55 +0100
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-12 21:56 +0000
Re: How to div only once to get remainder and quotient? jak <nospam@please.ty> - 2020-03-12 23:26 +0100
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-12 21:11 +0000
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-12 21:57 +0000
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-12 22:23 +0000
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-13 01:05 +0000
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-13 11:33 +0100
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-13 11:03 +0000
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-13 14:31 +0100
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-13 15:12 +0000
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-13 18:03 +0100
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-13 18:01 +0000
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-13 19:06 +0100
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-13 19:12 +0000
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-13 13:34 +0000
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-13 15:00 +0000
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-13 20:34 +0000
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-13 21:41 +0000
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-14 01:47 +0000
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-14 12:24 +0000
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-14 16:35 +0000
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-14 18:05 +0000
Re: How to div only once to get remainder and quotient? already5chosen@yahoo.com - 2020-03-13 03:52 -0700
Re: How to div only once to get remainder and quotient? Guillaume <message@bottle.org> - 2020-03-13 16:41 +0100
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-13 16:07 +0000
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-13 18:10 +0100
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-13 19:32 +0000
Re: How to div only once to get remainder and quotient? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-13 16:08 -0400
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-13 20:50 +0000
Re: How to div only once to get remainder and quotient? jameskuyper@stellarscience.com - 2020-03-13 16:05 -0700
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-13 23:42 +0000
Re: How to div only once to get remainder and quotient? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-13 19:59 -0400
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-14 00:07 +0000
Re: How to div only once to get remainder and quotient? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-13 20:27 -0400
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-14 01:37 +0000
Re: How to div only once to get remainder and quotient? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-04-02 07:45 -0700
Re: How to div only once to get remainder and quotient? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-04-02 08:09 -0700
Re: How to div only once to get remainder and quotient? gazelle@shell.xmission.com (Kenny McCormack) - 2020-04-02 16:03 +0000
Re: How to div only once to get remainder and quotient? Öö Tiib <ootiib@hot.ee> - 2020-04-04 04:31 -0700
Invitations (Was: How to div only once to get remainder and quotient?) gazelle@shell.xmission.com (Kenny McCormack) - 2020-04-04 17:04 +0000
Re: Invitations (Was: How to div only once to get remainder and quotient?) Öö Tiib <ootiib@hot.ee> - 2020-04-07 00:10 -0700
Re: How to div only once to get remainder and quotient? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-13 14:30 -0400
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-13 20:54 +0000
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-13 23:10 +0000
Re: How to div only once to get remainder and quotient? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-13 20:18 -0400
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-14 00:34 +0000
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-14 01:47 +0000
Re: How to div only once to get remainder and quotient? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-03-13 14:39 -0600
Re: How to div only once to get remainder and quotient? felix@palmen-it.de (Felix Palmen) - 2020-03-13 22:10 +0100
Re: How to div only once to get remainder and quotient? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-03-13 16:26 -0600
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-14 16:41 +0100
Re: How to div only once to get remainder and quotient? felix@palmen-it.de (Felix Palmen) - 2020-03-14 17:00 +0100
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-15 13:39 +0100
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-13 23:07 +0000
Re: How to div only once to get remainder and quotient? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-03-14 12:13 -0600
Re: How to div only once to get remainder and quotient? Bonita Montero <Bonita.Montero@gmail.com> - 2020-04-07 09:35 +0200
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