Re: A missing (?) function: exponentfp(x)

On 19/09/2024 12:24, Ilya Zakharevich wrote:
> On Thu, Sep 19, 2024 at 10:39:51AM +0200, Loïc Grenié wrote:
>>> Unfortunately, thinking of this more: no go.  You cannot pass through
>>> a double without a correction of large exponents…
>>      The proposed patch of Aurel passes only the first word of the mantissa
>>    to log2.
> Ah!  Sorry!  Did not pay enough attention (to rootpol.c, of all the places!)
>
> Unfortunately, the complex branch of dbllog2() seems to be majorly
> wrong…
>
> Using flog2() wrapper defined earlier in this thread:
>
>        	       flog2delta(x)=flog2(x)-log(abs(x))/log(2);
>    (03:01) gp > flog2delta(1+0.0008*I)
>    %284 = -4.6166226535255913560320062458846938056 E-7
>
> It seems that somebody wanted to write a Taylor series of order
> BYTES_IN_LONG/4 (in 4**(-abs(x-y))/2?), but stopped at writing the 0th
> term only…
I was quite puzzled by the complex branch too. But in any case when 
adding other types we would apply the same recursion for t_COMPLEX as 
for exponent(), i.e. maximum of result for real and imaginary parts.

Aurel