[MATH-904] FastMath.pow deviates from Math.pow for negative, finite base values with an exponent 2^52 < y < 2^53

• 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 20:51
• Updated: 04/Mar/13 18:53
• Resolved: 26/Nov/12 23:03

Description

As reported by Jeff Hain:

pow(double,double):
Math.pow(-1.0,5.000000000000001E15) = -1.0
FastMath.pow(-1.0,5.000000000000001E15) = 1.0
===> This is due to considering that power is an even
integer if it is >= 2^52, while you need to test
that it is >= 2^53 for it.
===> replace
"if (y >= TWO_POWER_52 || y <= -TWO_POWER_52)"
with
"if (y >= 2*TWO_POWER_52 || y <= -2*TWO_POWER_52)"
and that solves it.

Issue Links

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