Optimized Binary64 and Binary128 Arithmetic with GNU MPFR

We describe algorithms used to optimize the GNU MPFR library when the operands fit into one or two words. On modern processors, this gives a speedup for a correctly rounded addition, subtraction, multiplication, division or square root in the standard binary64 format (resp. binary128) between 1.8 and 3.5 (resp. between 1.6 and 3.2). We also introduce a new faithful rounding mode, which enables even faster computations. Those optimizations will be available in version 4 of MPFR.