The new logspace_sum function is not mapped to Rf_logspace_sum (in include/Rmath.h), which is different than its companions logspace_sub and logspace_add.
Also, its first argument is declared 'double*'. In my tests it does
not appear to alter the data pointed at so it would be nice to declare
it 'const double*'. (I like to use const in my code whenever possible
and the lack of const here forces an ugly cast or rewrite of code.)
Changes in R-devel (to be 3.3.0).