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To: libc-help@sourceware.org
From: Rosivaldo Fernandes Alves <rosivaldo.fa@gmail.com>
Subject: Complex division implementation: arbitrary sign taking?
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Date: Wed, 7 Apr 2021 14:48:02 -0300
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While trying to figure out how glibc implements complex division, I've 
found divtc3.c, where a division by zero is handled like written below.

       if (denom == 0.0 && (!isnan (a) || !isnan (b)))
	{
	  x = copysignl (INFINITY, c) * a;
	  y = copysignl (INFINITY, c) * b;
	}

The other branches of the algorithm handle signs in a very sensible 
manner, but the lines above seem rather arbitrary. Why to take the sign 
of c for both parts? Why does d play not part at all?

Thanks in advance.

Rosivaldo.