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Re: [PATCH] Optimize pow(x,0.0) = pow(1.0,y) = 1.0


Roger Sayle <roger at www dot eyesopen dot com> writes:

|> On Thu, 20 Feb 2003, Andrew Pinski wrote:
|> > Did you know that pow(0.0, 0.0) != 1.0?
|> 
|> I'm using as reference "IA-64 and Elementary Functions: Speed and
|> Precision", by Peter Markstein, HP Professional Books, 2000.
|> 
|> Section 12.6, entitled "Computing the Power Function" begins with
|> the paragraph.
|> 
|> 	To demonstrate the care needed for the power function, and
|> 	the many special cases required by C99 in an IEEE 754
|> 	implementation, we present a double precision power routine.
|> 	C99 requires the following results from the power function:
|> 
|> 	pow(x,+-0) returns 1 for any x, even a NaN.
|> 	...
|> 	pow(+-0,y) raises the divide-by-zero exception and returns
|> 		+-Inf for y < 0 and an odd integer, or +Inf for
|> 		other y < 0.
|> 	pow(+-0,y) returns +-0 for y > 0 and an odd integer, or
|> 		+0 for other y > 0.
|> 
|> I apologise that my reference is non-authorative.  Can someone
|> confirm the wording in the actual ISO C99 specification?

The C99 wording is slightly different, but equivalent.

Andreas.

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Andreas Schwab, SuSE Labs, schwab at suse dot de
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