Bill Allombert on Thu, 26 Oct 2006 20:55:24 +0200 |
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Re: [BUG?] log(2) flip/flopping |
On Wed, Oct 25, 2006 at 05:46:29PM -0700, Ilya Zakharevich wrote: > I discovered this by trying to investigate mysterious failures of > test suite of Math::Pari: > > ? log(2) > %1 = 0.6931471805599453094172321215 > ? \p 38 > realprecision = 38 significant digits > ? log(2) > %2 = 0.69314718055994530941723212145817656808 > ? \p 58 > realprecision = 67 significant digits (58 digits displayed) > ? log(2) > %3 = 0.6931471805599453094172321214581765680755001343602552541207 > ? \p 38 > realprecision = 38 significant digits > ? log(2) > %4 = 0.69314718055994530941723212145817656807 > > Is this change between ...08 and ...07 as expected? > > The code is in constlog2()... This bug is known and recorded as bug #498. The correct fix is to provide a version of constlog2 (and constpi and consteuler) which performs exact rounding. I suppose we could easily improve constlog2() so that the rounding is more frequently correct. Cheers, Bill