sepavloff added inline comments.
================ Comment at: compiler-rt/lib/builtins/fp_div_impl.inc:109 + +#if NUMBER_OF_HALF_ITERATIONS > 0 + // Starting with (n-1) half-width iterations ---------------- scanon wrote: > sepavloff wrote: > > atrosinenko wrote: > > > sepavloff wrote: > > > > It is good optimization. Could you please put a comment shortly > > > > describing the idea of using half-sized temporaries? > > > The idea is just "I guess this takes less CPU time and I have managed to > > > prove error bounds for it". :) Specifically, for float128, the rep_t * > > > rep_t multiplication will be emulated with lots of CPU instructions while > > > the lower half contain some noise at that point. This particular > > > optimization did exist in the original implementation for float64 and > > > float128. For float32 it had not much sense, I guess. Still, estimations > > > were calculated for the case of float32 with half-size iterations as it > > > may be useful for MSP430 and other 16-bit targets. > > The idea is clear but it require some study of the sources. I would propose > > to add a comment saying: > > ``` > > At the first iterations number of significant digits is small, so we may > > use shorter type values. Operations on them are usually faster. > > ``` > > or something like that. > This is absolutely standard in HW construction of pipelined iterative > dividers and square root units, so I'm not sure how much explanation is > really needed =) > This is absolutely standard in HW construction of pipelined iterative > dividers and square root units, so I'm not sure how much explanation is > really needed =) I think now the code has enough explanations to be easily understood by mere mortals also :) Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D85031/new/ https://reviews.llvm.org/D85031 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
