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From: Damian McGuckin <damianm@esi.com.au>
To: musl@lists.openwall.com
Subject: Possible Mistype in exp.c
Date: Mon, 28 Jan 2019 17:59:53 +1100 (AEDT)	[thread overview]
Message-ID: <alpine.LRH.2.02.1901281753250.16424@key0.esi.com.au> (raw)


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

Pacific Engineering Systems International, 277-279 Broadway, Glebe NSW 2037
Ph:+61-2-8571-0847 .. Fx:+61-2-9692-9623 | unsolicited email not wanted here
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             reply	other threads:[~2019-01-28  6:59 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-28  6:59 Damian McGuckin [this message]
2019-01-29 11:01 ` Szabolcs Nagy
2019-01-29 11:26   ` Damian McGuckin
2019-01-29 11:43     ` Szabolcs Nagy
2019-01-30  1:18       ` Damian McGuckin
2019-01-30  9:37         ` Szabolcs Nagy
2019-01-30 11:14           ` Damian McGuckin
2019-01-30 12:19             ` Szabolcs Nagy
2019-01-30 12:44               ` Alexander Monakov
2019-01-30 14:10                 ` Szabolcs Nagy
2019-02-01 23:26                   ` Morten Welinder
2019-02-02  3:39                     ` Szabolcs Nagy
2019-02-03  2:05                       ` Morten Welinder
2019-02-03  3:07                         ` Damian McGuckin
2019-04-03  1:13                       ` Floating Point Accuracy Damian McGuckin
2019-01-30 12:56           ` Possible Mistype in exp.c Damian McGuckin
2019-01-31  0:04             ` Szabolcs Nagy
2019-01-31  0:39               ` Damian McGuckin

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