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Re: How can I get an implementation of fmod()?

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Am 25.08.2023 um 09:19 schrieb Bonita Montero:
> Am 25.08.2023 um 08:25 schrieb Megumin:
>> How does remainder() in cmath works and is there any simple but fairly 
>> precise fmod that can be implemented without using double or long double?
>> I'm currently trying to implement fmodf(float x,float y) myself in 
>> assembly, and seems like in IEEE754, if I try to do as follows, the 
>> precision will f-up badly if x>>y in fact if x/y is more than 2^23 
>> this will just makes no sense at all.
>> r1 = f32(x);
>> r2 = f32(y);
>> r3 = div_f32(r1,r2);        //precision:2ulp
>> r4 = trunc(r3)// this is where things go bad if r3 is more than 2^23 
>> it does nothing and I will get no remainder.
>> r4 = multi_f32(r4,r2);
>> r4 = subtract_f32(r1,r4);
>> result = r4;
>>


The problem with your solution is that your div_f32 might loss
bits right from the mantissa but before the comma. This might
yield a result that is larger than the dividend.

> Look at the /sysdeps/ieee754/dbl-64/e_fmod.c glibc code. They've changed
> the code for the 8/1/2023 release and made the algorithm multiple times
> faster. The fmod() result has no precision loss.
> Don't bother with x87's FPREM. It's claimed to be excact but actally its
> an approximation on the CPU's I've recently checked (Zen1, Zen2, Zen4,
> Skylake).

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Thread

How can I get an implementation of fmod()? Megumin <chrisramirez0227@gmail.com> - 2023-08-24 23:25 -0700
  Re: How can I get an implementation of fmod()? Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-25 09:19 +0200
    Re: How can I get an implementation of fmod()? Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-25 09:35 +0200
  Re: How can I get an implementation of fmod()? Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-25 09:49 +0200
  Re: How can I get an implementation of fmod()? James Kuyper <jameskuyper@alumni.caltech.edu> - 2023-08-25 04:34 -0400
    Re: How can I get an implementation of fmod()? Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-25 10:37 +0200
      Re: How can I get an implementation of fmod()? Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-25 10:43 +0200
        Re: How can I get an implementation of fmod()? Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-25 11:20 +0200
          Re: How can I get an implementation of fmod()? Megumin <chrisramirez0227@gmail.com> - 2023-08-30 22:52 -0700
            Re: How can I get an implementation of fmod()? Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-31 11:00 +0200
            Re: How can I get an implementation of fmod()? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-08-31 21:48 +0100
            Re: How can I get an implementation of fmod()? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-08-31 14:37 -0700
    Re: How can I get an implementation of fmod()? James Kuyper <jameskuyper@alumni.caltech.edu> - 2023-08-25 04:44 -0400

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