Behavior of mpf_eq near zero

tg at tg at
Mon Apr 13 12:19:14 UTC 2015

Vincent Lefevre <vincent at> writes:

  The manual poorly specifies this function since it doesn't say what
  the first bits of a number are. For instance, the first 3 bits of
  are "0.00" thus are equal. So, you need to introduce the concept
  of normalization, and possibly take zero apart since it cannot be
I think that interpretation is a bit odd.  The same argument would make
17 and 4711 mpf_eq to 10 bits since these numbers are are 000000000010001
and 00000000001001001100111...

  > Please don't use this function.  At least use mpf_reldiff, or even
  > better, use the mpfr GMP extension library.
  I agree, though I really think that mpf_eq should be properly
  specified. And how about saying that this function is obsolete
  and planning to remove it in the future?

I agree with the latter.  The function is broken, it has no reasonable
mathematical interpretation.  (I take full responsibility for this, since
I wrote it.)

Please encrypt, key id 0xC8601622

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