Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c++ > #121703

Re: a MSVC and glibc-compatible fmod()

From Michael S <already5chosen@yahoo.com>
Newsgroups comp.lang.c++
Subject Re: a MSVC and glibc-compatible fmod()
Date 2025-02-24 17:33 +0200
Organization A noiseless patient Spider
Message-ID <20250224173345.000076a5@yahoo.com> (permalink)
References (1 earlier) <vphn0u$12go8$1@dont-email.me> <vphppf$138sj$1@raubtier-asyl.eternal-september.org> <vphr2t$13ih6$1@dont-email.me> <20250224162246.000016c6@yahoo.com> <vpi25t$1520i$1@dont-email.me>

Show all headers | View raw

On Mon, 24 Feb 2025 15:10:53 -0000 (UTC)
Muttley@DastardlyHQ.org wrote:

> On Mon, 24 Feb 2025 16:22:46 +0200
> Michael S <already5chosen@yahoo.com> wibbled:
> >On Mon, 24 Feb 2025 13:09:50 -0000 (UTC)
> >Muttley@DastardlyHQ.org wrote:  
> >> If the values are so large or small that you start to get floating
> >> point based errors then you should probably be using integer
> >> arthmetic or a large number library anyway like GMP anyway.
> >>   
> >
> >Your method will sometimes produce results that are 1 LSB off
> >relatively to IEEE-754 prescription when values are neither small nor
> >large.
> >And sometimes 1 LSB off means that result is 2x off.
> >For example, for x=0.9999999999999999, y=0.9999999999999998 your
> >method produces 2.2204460492503126e-16. A correct result is, of
> >course, 1.1102230246251565e-16  
> 
> Frankly I doubt anyone would care, its zero in all but name.
> 
> >Also, I don't think that your method is any faster than correct
> >methods.  
> 
> Don't know, but its only 3 mathematical operations all of which can
> be done by the hardware so its going to be pretty fast.
> 
> 

Looks like 4 operations to me - division, truncation, subtraction,
multiplication. If compiler takes it literally, which he probably
should if compiled without special non-standard-conforming flags like
-fast-math, then there are 5 operations - double->int and
int->double conversions instead of truncation

Nevertheless, after a bit of thinking I concur that your formula is
faster than 100% correct methods. Initially, I didn't took into account
all difficulties that correct methods have to face in cases of very
large x to y ratios.

However your method is approximately the same speed as *mostly correct*
method shown in my post above. May be, yours is even a little slower,
at least as long as we use good optimizing compiler and target modern
CPUs that support trunc() and fma() as fast hardware instructions.

Back to comp.lang.c++ | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-24 11:48 +0100
  Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-24 12:00 +0000
    Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-24 13:48 +0100
      Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-24 13:09 +0000
        Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-24 14:22 +0100
          Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-24 17:13 +0200
            Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-24 16:19 +0100
              Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-24 17:52 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-25 09:09 +0100
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-25 16:17 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-25 17:26 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-25 16:45 +0100
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-25 16:57 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-25 19:17 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-25 18:58 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-26 00:36 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-26 04:15 +0100
                Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-26 08:16 +0000
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-26 14:27 +0200
                Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-26 14:39 +0000
                FP_CONTRACT was : a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-28 16:28 +0200
                Re: FP_CONTRACT was : a MSVC and glibc-compatible fmod() Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-03-01 08:35 -0800
        Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-24 16:22 +0200
          Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-24 15:10 +0000
            Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-24 17:33 +0200
              Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-24 16:48 +0000
  Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-02-24 22:21 +0000
    Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-25 07:37 +0100
      Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-02-25 23:03 +0000
        Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-26 02:00 +0200
        Re: a MSVC and glibc-compatible fmod() Wuns Haerst <Wuns.Haerst@wurstfabrik.at> - 2025-02-26 04:01 +0100
    Re: a MSVC and glibc-compatible fmod() Muttley@DastardlyHQ.org - 2025-02-25 08:24 +0000
  Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-02-27 21:16 +0000
    Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-28 07:59 +0100
    Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-02-28 12:35 +0200
      Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-02-28 18:12 +0000
    Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-28 19:23 +0100
  Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-02-28 18:30 +0000
    Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-28 19:31 +0100
      Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-02-28 19:47 +0000
        Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-02-28 20:49 +0100
          Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-03-01 14:37 +0000
            Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-01 16:58 +0100
              Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-03-01 17:11 +0000
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-01 21:02 +0100
                Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-03-01 20:32 +0000
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-01 21:37 +0100
                Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-03-01 20:45 +0000
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 09:40 +0100
  Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-01 22:55 +0200
    Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 18:54 +0200
      Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 17:59 +0100
  Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 15:41 +0200
    Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 17:10 +0100
      Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-03-02 16:22 +0000
        Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 17:26 +0100
          Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 19:07 +0200
            Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 18:09 +0100
              Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 18:11 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 19:52 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 18:55 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 20:09 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 19:14 +0100
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 19:57 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 22:58 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 12:52 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-03 18:10 +0200
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-03 23:55 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-07 09:51 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-03 18:20 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 17:30 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-03 19:27 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 18:39 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-03 02:01 +0200
        Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 19:37 +0200
          Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 18:41 +0100
            Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-02 20:00 +0200
              Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-02 19:01 +0100
      Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 01:31 +0200
        Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 07:41 +0100
          Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 11:08 +0200
            Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 10:31 +0100
              Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 11:46 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 10:54 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 12:09 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 11:21 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 14:09 +0200
                Re: a MSVC and glibc-compatible fmod() Mr Flibble <leigh@i42.co.uk> - 2025-03-09 15:26 +0000
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 17:02 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 19:55 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 19:10 +0100
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 19:27 +0100
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 17:23 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 20:04 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 19:11 +0100
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 20:11 +0100
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 07:24 +0100
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 10:46 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 14:26 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 13:45 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 16:33 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 15:46 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 16:59 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 16:11 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 17:43 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 17:13 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 19:51 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 19:00 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 20:38 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 22:34 +0100
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 22:36 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 12:47 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 23:52 +0100
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 23:57 +0100
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-11 09:34 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 12:29 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-11 12:12 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 13:34 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-11 13:10 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 14:55 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-11 14:08 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 15:46 +0200
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 13:51 +0200
                Re: a MSVC and glibc-compatible fmod() James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-03-11 14:21 -0400
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-11 20:28 +0200
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-16 13:48 +0200
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-10 13:17 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 12:53 +0100
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-10 12:54 +0100
              Re: a MSVC and glibc-compatible fmod() wij <wyniijj5@gmail.com> - 2025-03-09 18:51 +0800
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 12:56 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 14:23 +0200
                Re: a MSVC and glibc-compatible fmod() Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-09 13:39 +0100
                Re: a MSVC and glibc-compatible fmod() Michael S <already5chosen@yahoo.com> - 2025-03-09 14:56 +0200

csiph-web