On Thu, 27 Feb 2003, Paul A. Bristow wrote: > Yes - this looks potentially rather useful for some tasks, especially embedded > systems. > Why on earth didn't the language include fixed point and/or fractional types?
Well in order for fractions to be really useful, that is to support exact values for basic arithmetic, you would also need a arbitrary size integer class as the numerator and denominator can get very large very fast unless the fraction is automatically reduces after each operation and even than the numbers can get big. > As you observe, the increased accuracy compared to float (just a little too > small for some measurements like weights) but with half the memory of double, > and of course the integer/binary nature are sometimes useful. I am curious why you say a float is "just a little tool small for some measurements like weights". I have always used doubles, but I never put much thought into it. > Do you have any test programs? > > Have you made any comparison with float and double speeds? No. However in general fixed point math is comparable to speed to floating point math on systems with a good FPU. However, you might gain some speed when most operations or integer based and a floating point number is only used occasionally (say for taking an average) as you would save cycles on the conversion from an int to a floating point number. Of course, fixed point is extremely useful on FPU less systems and the speed up will be substantial. However, my library lacks fixed point versions of the basic math functions (sqrt, exp, sin, etc...), making it of limited usefulness speed wise on a FPU less system. If someone knows of a C library that provided these routines I might consider porting it. Also, When using fixed point math you might lose some precision (if going from a double to a 32 bit fixed point number as a 64 bit would be too slow). > > HTH to encourage you. > > Paul > --- http://kevin.atkinson.dhs.org _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
