Fix cexp overflow (bug 13892)

[Andreas Jaeger]

On 03/22/2012 06:01 PM, Joseph S. Myers wrote:
> This patch fixes bug 13892, internal overflows in cexp.  There are
> clear-cut cases, where both real and imaginary parts should be finite
> for a narrow range of real parts of the input even when exp (real part
> of input) itself overflows, and also cases where one part should be
> finite and the other infinite (because of the case of subnormals in
> the input, this can occur with exponents more than twice as large as
> that that would overflow exp - or of course with any finite positive
> exponent if the real part of the input is zero).  The approach is
> simply to subtract a suitable integer from the real part of the input
> and multiply by exp of that integer, up to twice, to reduce the
> exponent in cases that may have one of the parts of the result finite.
>
> (There are no underflow problems with the cexp implementation, but I put
> some tests for underflow cases - subnormal results - in anyway, since they
> didn't seem to be covered by the testsuite before.)

thanks, this is ok,

Andreas
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