- d
- the value to compute the ed- 1 of.
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Returns the closest double approximation of ed- 1. If the argument is very close to 0, it is much more accurate to use expm1(d)+1 than exp(d) (due to cancellation of significant digits). The returned result is within 1 ulp (unit in the last place) of the real result.
For any finite input, the result is not less than -1.0. If the real result is within 0.5 ulp of -1, -1.0 is returned.
Special cases: