musl - Possible Mistype in exp.c

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Date: Mon, 28 Jan 2019 17:59:53 +1100 (AEDT)
From: Damian McGuckin <damianm@....com.au>
To: musl@...ts.openwall.com
Subject: Possible Mistype in exp.c

In 1.1.21 in exp.c

        if (x < -708.39641853226410622) {
             /* underflow if x!=-inf */
             FORCE_EVAL((float)(-0x1p-149/x));
             if (x < -745.13321910194110842)

The constant also appears is expf.c.

For floats and for floats, the constant

 	0x1p-149

is the smallest non-zero finite number and will do the right thing.

Using that with doubles will not trigger an underflow exception.

I believe that for doubles, this needs to be

 	0x1p-1074

for doubles, i.e. 0x1p-1022 * 0x1p-52 if you want a conceptual match.

Regards - Damian

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