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copysign(+X, +Y, -Result)

Compose a number from magnitude and sign
X
A number
Y
A number
Result
Output: number

Description

This predicate is used by the ECLiPSe compiler to expand evaluable arithmetic expressions. So the call to copysign(X, Y, Result) is equivalent to
Result is copysign(X, Y)
which should be preferred for portability.

Result is a number of the same type and absolute value as X, but with the sign of Y. Result is therefore either identical to X or to -X.

This function correctly considers the sign bits of special floating point values, such as -0.0, infinities and NaNs.

In coroutining mode, if X or Y is uninstantiated, the predicate delays.

Modes and Determinism

• copysign(+, +, -) is det

Exceptions

(4) instantiation fault
X or Y is not instantiated (non-coroutining mode only).
(20) arithmetic exception
Sign of Y is not known
(24) number expected
Number is not of a numeric type.

Examples

Success:
Result is copysign( 3.0, 2.0).	% gives Result =  3.0
Result is copysign( 3.0,-2.0).	% gives Result = -3.0
Result is copysign(-3.0, 2.0).	% gives Result =  3.0
Result is copysign(-3.0,-2.0).	% gives Result = -3.0

Result is copysign( 3.0,-0.0).	% gives Result = -3.0
Result is copysign( 3.0, 0.0).	% gives Result =  3.0
Result is copysign( 3.0, 0).	% gives Result =  3.0

Result is copysign( 3, -1.0).	% gives Result = -3
Result is copysign( 1, -0.0).	% gives Result = -1
Result is copysign( 3.0, -1).	% gives Result = -3.0
Result is copysign(-3.0,  1).	% gives Result =  3.0

Error:
Result is copysign(3.0, -0.1__0.1).	% arithmetic exception