two questions on GMP & C float

Vojtěch Bubník bubnikv at
Fri May 15 17:37:06 CEST 2009

Hello GMP group.

We are using GMP extensively for our geometric calculations like intersection lines between two 3d meshes etc. I am combining boost interval arithmetics with GMP to speed up predicates. That works really well. The interval arithmetics library is switching FPU rounding mode down. Does GMP use FPU or may I leave rounding mode set to "down" for the interval arithmetics library to work even during calls to GMP?

Another question. If I know beforehand that the floats I am converting to mpq have some right mantissa bits cleared, will the mpq numbers be faster? Will the mpq representation use less bits? Will it help, if I write my own conversion function from float with limited mantissa to mpq?

Thanks, Vojtech

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