Is faster method to add doubledouble possible within sleef? about sleef HOT 2 CLOSED

It is not very clear if this method improves the computation speed.

Decker's paper is published in 1971, and in my understanding Knuth later came up with a branchless method for doing the same thing. The branchless version has only one more addition, and usually this is faster. SLEEF's routines are based on the branchless version.

In the stackoverflow page, he says "This definition of Add22 uses 11 additions instead of 20 but it requires some additional code to determine if |ah| >= |bh|," but my implementation of ddadd2_d2_d2_d2 has only 8 additions. Note that my implementation does not try to achieve full DD precision.

Actually I once considered if the Decker's algorithm is faster, and I concluded that the current version is better.

from sleef.

@shibatch, that's a interesting insight into the implemenation details, thanks.

from sleef.