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| author | zimmerma <zimmerma@280ebfd0-de03-0410-8827-d642c229c3f4> | 2021-02-03 15:44:41 +0000 |
|---|---|---|
| committer | zimmerma <zimmerma@280ebfd0-de03-0410-8827-d642c229c3f4> | 2021-02-03 15:44:41 +0000 |
| commit | bd28c414db0faf86ae13081c0d0c75aa9dc8a606 (patch) | |
| tree | 740ee0dd0301f5de5cd258ee3be7ec5dd4f13f49 /src/log2p1.c | |
| parent | 944f9eaff82e2f56d5f9e43b766aa09eb4ed4630 (diff) | |
| download | mpfr-bd28c414db0faf86ae13081c0d0c75aa9dc8a606.tar.gz | |
[src/log2p1.c] added note about underflow
git-svn-id: https://scm.gforge.inria.fr/anonscm/svn/mpfr/trunk@14351 280ebfd0-de03-0410-8827-d642c229c3f4
Diffstat (limited to 'src/log2p1.c')
| -rw-r--r-- | src/log2p1.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/src/log2p1.c b/src/log2p1.c index 835f77298..197e2876b 100644 --- a/src/log2p1.c +++ b/src/log2p1.c @@ -126,7 +126,10 @@ mpfr_log2p1 (mpfr_ptr y, mpfr_srcptr x, mpfr_rnd_t rnd_mode) mpfr_const_log2 (lg2, MPFR_RNDN); mpfr_div (t, t, lg2, MPFR_RNDN); /* t = log2(1+x) * (1 + theta)^3 where |theta| < 2^-prec, - for prec >= 2 we have |(1 + theta)^3 - 1| < 4*theta. */ + for prec >= 2 we have |(1 + theta)^3 - 1| < 4*theta. + Note: contrary to log10p1, no underflow is possible in extended + exponent range, since for tiny x, |log2(1+x)| ~ |x|/log(2) >= |x|, + and x is representable, thus x/log(2) too. */ if (MPFR_LIKELY (MPFR_CAN_ROUND (t, prec - 2, Ny, rnd_mode))) break; |