[Boost-users] [interval] using crlibm for transcendental functions

From: Tobias Munk (munk_tobias_at_[hidden])
Date: 2007-01-25 04:25:52

I am using a custom rounding policy for transcendental functions, based on crlibm and defined in the manner of

libs/numeric/interval/examples/transc.cpp

In the documentation of crlibm, it is recommended to call the init function crlibm_init() before calling one of their transcendental functions. My question now is: does anybody know if calling this init function collides with any of the boost.numeric.interval internal algorithms? 

On i686 and amd64 crlibm_init() instructs the FPU not to use extended arithmetics:

/* An init function which sets FPU flags when needed */
unsigned long long crlibm_init() {
  /* Set FPU flags to use double, not double extended, 
     with rounding to nearest */  
  cw = (_FPU_DEFAULT & ~_FPU_EXTENDED)|_FPU_DOUBLE;
  _FPU_SETCW(cw);
...
}

Is it necessary to reset the old state after a call of a crlibm function, for correct interval arithmetics, or is one call of crlibm_init() for the whole program sufficient?

Thanks,

Tobias Munk
                 
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