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Re: [PATCH v2] Simplify pow with constant

On 08/17/2017 09:43 AM, Alexander Monakov wrote:
> On Thu, 17 Aug 2017, Wilco Dijkstra wrote:
> 
>> This patch simplifies pow (C, x) into exp (x * C1) if C > 0, C1 = log (C).
> 
> Note this changes the outcome for C == +Inf, x == 0 (pow is specified to
> return 1.0 in that case, but x * C1 == NaN).  There's another existing
> transform with the same issue, 'pow(expN(x), y) -> expN(x*y)', so this is
> not a new problem.
That may be part of the reason why they're guarded with -ffast-math.  In
addition to the changes in accuracy.  I haven't followed those
transformations on the GCC side to know with any certainty.

jeff
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