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Groups > comp.lang.c++ > #124686
| From | Michael S <already5chosen@yahoo.com> |
|---|---|
| Newsgroups | comp.lang.c++, comp.lang.c |
| Subject | Re: why is there not a ipow version of pow? |
| Date | 2026-08-12 22:43 +0300 |
| Organization | A noiseless patient Spider |
| Message-ID | <20260812224333.000065c4@yahoo.com> (permalink) |
| References | (9 earlier) <115feje$3nf1$1@raubtier-asyl.eternal-september.org> <115ffag$1659$9@dont-email.me> <115g94d$2pb62$1@paganini.bofh.team> <115h9mb$kpdk$1@dont-email.me> <115hjka$o7k2$1@kst.eternal-september.org> |
Cross-posted to 2 groups.
On Wed, 12 Aug 2026 03:58:16 -0700 Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote: > David Brown <david.brown@hesbynett.no> writes: > [...] > > And I thought it is entirely obvious that when you are actually > > implementing a floating point power function on a binary computer > > using floating point formats specified in binary, it is most > > efficient to use base 2 for the log and anti-log. If you had a > > floating point format that used base 10, you'd probably want to use > > base 10 for the log and anti-log. > > Is it obvious? It had never occurred to me. > > log and exp are certainly more mathematically straightforward in > base e than in other bases. Only near x=1 for log(x) and near x=0 for exp(x). > Of course floating-point is typically > binary, but I didn't know that would imply that log(x) base 2 is > easier to compute that log(x) base e. I've always assumed that > base e is more efficient than other bases. You are mostly wrong. David is mostly correct. > > Also, I vaguely recall that though x**y is mathematically equivalent > to exp(y * log(x)), that's not the most efficient and/or accurate > way to compute it. > Apart from corner cases, it is the most efficient. And I am pretty sure that it's sufficiently accurate for most uses, including you typical C library. I did no deep numeric analysis, but my intuition suggest that as long as underlaying primitives, i.e. log2 and 2**x, are well implemented, i.e. their maximal error is under 0.6 ULP, then the worst case error of combined calculation should be below 2.5 ULP and most likely even lower than that. Which is good enough. For more than 50% of inputs you will end within 1 ULP. Of course, you don't do it stupidly. You start by splitting a with frexp() and splitting b to integer and fractional, probably with fractional in range [-0.5:0.5]. Then you take away trivial parts, i.e integer power of two. But then you come to the main part and this part is as David suggested.
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why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-11 03:01 -0500
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 13:11 +0200
Re: why is there not a ipow version of pow? bart <bc@freeuk.com> - 2026-08-11 12:45 +0100
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 14:34 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 14:55 +0200
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-11 15:19 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 15:27 +0200
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-11 16:08 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 16:18 +0200
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-11 17:11 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 17:20 +0200
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-11 17:32 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 17:39 +0200
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-11 18:33 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 18:39 +0200
Re: why is there not a ipow version of pow? Michael S <already5chosen@yahoo.com> - 2026-08-11 23:31 +0300
Re: why is there not a ipow version of pow? James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-08-11 11:46 -0400
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-11 18:35 +0200
Re: why is there not a ipow version of pow? antispam@fricas.org (Waldek Hebisch) - 2026-08-11 22:53 +0000
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-12 10:08 +0200
Re: why is there not a ipow version of pow? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-12 03:58 -0700
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-12 13:31 +0200
Re: why is there not a ipow version of pow? Michael S <already5chosen@yahoo.com> - 2026-08-12 22:43 +0300
Re: why is there not a ipow version of pow? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-12 13:44 -0700
Re: why is there not a ipow version of pow? Michael S <already5chosen@yahoo.com> - 2026-08-13 00:24 +0300
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-12 16:49 -0500
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-13 08:38 +0200
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-13 18:59 -0500
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-13 18:51 -0700
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-14 00:58 -0500
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 12:08 -0700
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-14 15:48 -0500
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 13:51 -0700
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-14 16:40 -0500
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 19:24 -0700
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-14 22:51 -0500
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 22:33 -0700
Re: why is there not a ipow version of pow? Ross Finlayson <ross.a.finlayson@gmail.com> - 2026-08-15 10:40 -0700
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-15 11:41 -0700
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-17 14:48 -0500
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-16 14:58 -0700
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-14 08:57 +0200
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 12:46 -0700
Re: why is there not a ipow version of pow? James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-08-13 12:59 -0400
Re: why is there not a ipow version of pow? antispam@fricas.org (Waldek Hebisch) - 2026-08-12 20:23 +0000
Re: why is there not a ipow version of pow? scott@slp53.sl.home (Scott Lurndal) - 2026-08-11 18:19 +0000
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 20:21 +0200
Re: why is there not a ipow version of pow? scott@slp53.sl.home (Scott Lurndal) - 2026-08-11 21:10 +0000
Re: why is there not a ipow version of pow? Michael S <already5chosen@yahoo.com> - 2026-08-12 00:42 +0300
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-12 06:41 +0200
Re: why is there not a ipow version of pow? scott@slp53.sl.home (Scott Lurndal) - 2026-08-12 14:19 +0000
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-12 16:56 +0200
Re: why is there not a ipow version of pow? scott@slp53.sl.home (Scott Lurndal) - 2026-08-12 15:32 +0000
Re: why is there not a ipow version of pow? Michael S <already5chosen@yahoo.com> - 2026-08-12 22:05 +0300
Re: why is there not a ipow version of pow? Paul <nospam@needed.invalid> - 2026-08-12 19:09 -0400
Re: why is there not a ipow version of pow? Michael S <already5chosen@yahoo.com> - 2026-08-11 21:58 +0300
Re: why is there not a ipow version of pow? Ross Finlayson <ross.a.finlayson@gmail.com> - 2026-08-11 21:44 -0700
Re: why is there not a ipow version of pow? bart <bc@freeuk.com> - 2026-08-11 15:45 +0100
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 16:56 +0200
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-11 17:23 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 17:24 +0200
Re: why is there not a ipow version of pow? bart <bc@freeuk.com> - 2026-08-11 16:23 +0100
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 17:26 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 17:54 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 18:40 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-12 08:49 +0200
Re: why is there not a ipow version of pow? Paul <nospam@needed.invalid> - 2026-08-12 09:11 -0400
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-12 16:05 +0200
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-12 12:40 -0700
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-13 15:46 +0200
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-13 14:28 -0700
Re: why is there not a ipow version of pow? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-11 16:20 -0700
Re: why is there not a ipow version of pow? bart <bc@freeuk.com> - 2026-08-11 18:43 +0100
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 19:56 +0200
Re: why is there not a ipow version of pow? bart <bc@freeuk.com> - 2026-08-11 20:41 +0100
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-12 06:42 +0200
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-12 10:23 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 20:24 +0200
Re: why is there not a ipow version of pow? bart <bc@freeuk.com> - 2026-08-11 20:27 +0100
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-12 06:45 +0200
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-11 17:16 +0200
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-11 15:17 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 15:28 +0200
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-11 16:43 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-11 16:47 +0200
Re: why is there not a ipow version of pow? David Brown <david.brown@hesbynett.no> - 2026-08-11 17:24 +0200
Re: why is there not a ipow version of pow? Paul <nospam@needed.invalid> - 2026-08-11 09:36 -0400
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-11 16:42 -0500
Re: why is there not a ipow version of pow? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-08-11 19:15 +0200
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-11 16:41 -0500
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-11 16:49 -0500
Re: why is there not a ipow version of pow? bart <bc@freeuk.com> - 2026-08-11 23:28 +0100
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-11 17:51 -0500
Re: why is there not a ipow version of pow? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-11 15:33 -0700
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-11 17:49 -0500
Re: why is there not a ipow version of pow? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-11 16:19 -0700
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-12 00:32 -0500
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-12 14:08 +0200
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-12 18:40 +0200
Re: why is there not a ipow version of pow? Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-14 02:50 +0000
Re: why is there not a ipow version of pow? Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-12 04:26 +0000
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-12 01:37 -0500
Re: why is there not a ipow version of pow? Paul <nospam@needed.invalid> - 2026-08-13 00:12 -0400
Re: why is there not a ipow version of pow? Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-14 11:22 +0800
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-14 01:00 -0500
Re: why is there not a ipow version of pow? Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-14 14:47 +0800
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-14 13:54 -0500
Re: why is there not a ipow version of pow? Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-16 22:49 +0000
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-17 14:56 -0500
Re: why is there not a ipow version of pow? Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-17 23:53 +0000
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-17 19:59 -0500
Re: why is there not a ipow version of pow? Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-18 02:47 +0000
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-17 15:17 -0500
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 12:03 -0700
Re: why is there not a ipow version of pow? Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-15 03:51 +0800
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 12:52 -0700
Re: why is there not a ipow version of pow? Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-15 04:01 +0800
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 13:27 -0700
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 13:29 -0700
Re: why is there not a ipow version of pow? Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-15 04:49 +0800
Re: why is there not a ipow version of pow? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-14 20:32 -0700
Re: why is there not a ipow version of pow? bart <bc@freeuk.com> - 2026-08-12 11:28 +0100
Re: why is there not a ipow version of pow? Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-12 23:52 +0000
Re: why is there not a ipow version of pow? Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-13 17:19 +0800
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-13 19:07 -0500
Re: why is there not a ipow version of pow? Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-14 10:58 +0800
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-14 01:14 -0500
Re: why is there not a ipow version of pow? Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-08-17 06:40 +0000
Re: why is there not a ipow version of pow? Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-17 21:40 +0800
Re: why is there not a ipow version of pow? Lynn McGuire <lynnmcguire5@gmail.com> - 2026-08-18 00:42 -0500
Re: why is there not a ipow version of pow? Bonita Montero <Bonita.Montero@gmail.com> - 2026-08-18 09:34 +0200
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