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Mr. Niakwa
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« on: January 28, 2009, 03:41:25 pm »
Bug notification

We have uncovered a bug in NPL Release 5 runtimes for SuSE Linux and SCO Unix that affects trigonometric functions.

In this bug, an obscure series of calculations caused a value of -90 to be stored internally as (-90000000000000E-12), which is numerically the same as -90.  The math coprocessor code loads the value, and mistakenly detects the internal value as an underflow to zero, so it uses the value of  0 instead of -90 for the trig function. 

The bug doesn't affect Windows runtimes because a different method of testing for underflow is used. 

The bug can affect any of the trig functions but only when:
1) $OPTIONS byte 16 is HEX(01)
2) the trig function's argument is negative
3) the argument is stored internally with a negative exponent (e.g. -900E-1). 

The bug can be avoided completely by setting $OPTIONS byte 16 to HEX(00), which is the default.
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