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From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.lang.c
Subject: Re: Implementation of pow(3m) function
Keywords: math-library exponentiation C
Message-ID: <13474@smoke.BRL.MIL>
Date: 3 Aug 90 21:21:40 GMT
References: <1990Aug2.120706.25713@bnrgate.bnr.ca>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 10

In article <1990Aug2.120706.25713@bnrgate.bnr.ca> mleech@bcarh342.bnr.ca (Marcus Leech) writes:
>I'm wondering about the efficiency of "standard" implementations of this
>  (and other) math library functions for C.  Does pow(3m) conventionally
>  use a logarithm table, or is it (ugh!) iterative, or some B.O.T?

All common implementations of pow(x,y) basically perform exp(log(x)*y),
but they add some twists designed to avoid unnecessary overflow, or in
the case of 4.3BSD, to implement the IEEE FP funny numbers.  Thus there
is often a considerable amount of additional bookkeeping computation
beyond the log() and exp() evaluations that one would expect.