[MATH-905] FastMath.[cosh, sinh] do not support the same range of values as the Math counterparts

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0
• Fix Version/s: 3.1
• Assignee: Unassigned
• Reporter: Thomas Neidhart
• Created: 20/Nov/12 20:54
• Updated: 04/Mar/13 18:53
• Resolved: 26/Nov/12 13:25

Description

As reported by Jeff Hain:

cosh(double) and sinh(double):
Math.cosh(709.783) = 8.991046692770538E307
FastMath.cosh(709.783) = Infinity
Math.sinh(709.783) = 8.991046692770538E307
FastMath.sinh(709.783) = Infinity
===> This is due to using exp( x )/2 for values of |x|
above 20: the result sometimes should not overflow,
but exp( x ) does, so we end up with some infinity.
===> for values of |x| >= StrictMath.log(Double.MAX_VALUE),
exp will overflow, so you need to use that instead:
for x positive:
double t = exp(x*0.5);
return (0.5*t)*t;
for x negative:
double t = exp(-x*0.5);
return (-0.5*t)*t;

Issue Links

• is related to: MATH-580 FastMath Performance Test should use larger ranges where the functions support them