sin.c: reverted r795 and r796 and applied simple fix for overflow

BUGS: clarified handling of intermediate overflow


git-svn-id: svn://scm.gforge.inria.fr/svn/mpc/trunk@802 211d60ee-9f03-0410-a15a-8952a2c7a4e4

1 files changed, 10 insertions, 5 deletions

diff --git a/BUGS b/BUGS
index 68bcd23..b7ded65 100644
--- a/BUGS
+++ b/BUGS
@@ -1,5 +1,10 @@
-- No checks are made for intermediate overflows, which may occur
-  in the middle of the algorithms although the final result
-  may be representable.
-  More precisely for cos(x+i*y) = cos(x)*cosh(y) - sin(x)*sinh(y)*I,
-  if an overflow occurs in cosh(y), we assume cos(x)*cosh(y) overflows too.
+- No checks are made for intermediate over- or underflows, which may occur
+  in the middle of the algorithms although the final result may be
+  representable.
+  For instance, if in the computation of Im (cos(x+i*y)) = -sin(x)*sinh(y)
+  an overflow occurs in sinh(y), the value sign(Im (cos(x+i*y))) * inf
+  is returned, even if sin(x) is sufficiently close to 0 such that
+  sin(x)*sinh(y) is representable. If furthermore an underflow occurred
+  in sin(x) (which has not been observed in practice), then the return
+  value would be NaN*(+-inf)=NaN.
+