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Re: 11706 vs ([lno] Canonical iv creation)
Paolo Carlini wrote:
Richard Guenther wrote:
I'm curious to how the standard actually defines std::pow()s accuracy
here though. I know we're not optimizing ::pow(x, 4) to the above
without -ffast-math because of accuracy concerns. So how does
std::pow() relate to ::pow in terms of accuracy guarrantees?
Really interesting issue...
Anyway, from a practical point of view I'm not really worried, since:
1- Glibc uses internally the very same algorithm, at least on x86 (just
2- Which requires O(log n) multiplications and is discussed by Knuth in
Sec. 4.6.3 of the second volume. You can find it almost *everywhere*,
for instance also in SGI's power.
So there is no point in not optimizing ::pow(x, 4) without -ffast-math?