[Octave-bug-tracker] [bug #42583] log2() returns inaccurate result for many integer powers of 2, unlike Matlab

[Rik]

Follow-up Comment #20, bug #42583 (project octave):

The code for pow2 is in libinterp/corefcn/pow2.cc.  For doubles,


for (octave_idx_type i = 0; i < y.numel (); i++)
  y.xelem (i) = std::exp2 (x.xelem (i));


So, Octave is just making use of the C++ math library.

On my machine,


pow2 (-1026:-1020)
ans =

  1.4e-309  2.8e-309  5.6e-309  1.1e-308  2.2e-308  4.5e-308  8.9e-308


But this is just with very simple compile flags "-O2 -pipe".




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