I'm developing a program which represents angles internally as binary fractions (0x80000000 means 360°). To convert the angle to radians, I used M_PI originally, felt I needed more accuracy, and found that Linux has M_PIl, which has a few extra digits so that it is accurate as a ten-byte float (the processor's internal representation). DFBSD doesn't have M_PIl, so I wrote a preprocessor directive which uses M_PI if M_PIl doesn't exist. I run a test which adds sin 45° to sin 225° and such combinations around the circle, squares the errors, and adds them up.

printf("total sine error=%e\n",totsinerror); printf("total cosine error=%e\n",totcoserror); printf("total cis error=%e\n",totciserror); assert(totsinerror+totcoserror+totciserror<1e-29); //On Linux, the total error is 6e-39 and the M_PIl makes a big difference. //On DragonFly BSD, the total error is 5e-30 and M_PIl is absent. Pierre -- When a barnacle settles down, its brain disintegrates. Já não percebe nada, já não percebe nada.