Boost C++ Libraries: Ticket #12625: multiprecision acos() sometimes does not return

attachment set

steve@… — Sat, 26 Nov 2016 03:41:58 GMT

attachment → no-fp-ilogb0

patch for bug

cc changed

Sat, 26 Nov 2016 12:02:24 GMT

cc thibaut@… added

Sun, 27 Nov 2016 09:30:43 GMT

Hi,

Although I haven't yet been able to demonstrate that acos() can hang on amd64, I confirm that ilogb(zero) is also 0 for a multiprecision zero on this architecture, therefore comparing it to FP_ILPOGB0 does not make sense:

#include <iostream>
#include <boost/multiprecision/cpp_dec_float.hpp>
int main(int argc, char** argv) {
  boost::multiprecision::number<boost::multiprecision::cpp_dec_float<100> >
    zero("0.");
  std::cout << ilogb(zero) << std::endl;
  std::cout << FP_ILOGB0 << std::endl;
  return 0;
}

Kind regards, Thibaut.

status changed; resolution set

John Maddock — Sat, 03 Dec 2016 11:54:12 GMT

status new → closed
resolution → fixed

The attached patch fixes things for cpp_dec_float, but completely breaks other types in the library (as you would quickly discover running the regression tests). This is now fixed in develop in a series of commits:

https://github.com/boostorg/multiprecision/commit/138a9055e2edc68dca2e78ff97ffe6276c17fa0a https://github.com/boostorg/multiprecision/commit/26ceb6ef386f5fb879ddccca59cc3bdc57c124f3 https://github.com/boostorg/multiprecision/commit/c0df5b6747d09268256b59501c3cab746112268e

These mostly relate to issue #12581 but fix this one as well.