Leon, or, to make it simple: Q: why the test1 gives a correct result (31415) and the test4 gives an error (|significand| > 16777215). The test1 is the same as the test4, the only difference is the test4 has minus10000 as the first multiplicand. Pito
----- PŮVODNÍ ZPRÁVA ----- Od: "pito" <p...@volna.cz> Komu: leon.mau...@gmail.com, amforth-devel@lists.sourceforge.net Předmět: Re: [Amforth-devel] Float testing - small/large numbers Datum: 29.8.2010 - 20:01:01 > The test cases are designed specifically to se how > it handles large > and small numbers. The cases 1-3 are the same as > 4-6, the later have > only minus sign with those 10000 numbers. All the > results shall be > by design the integer number 31415 (visualised by > "10000 x Pi" - as > we do not have float format yet). The Pi is simply > multiplied or/and > divided by large numbers (as we do not have float > input yet, it is > done by several multiplication/division by 10000). > The results are: > > test1 > 31415 ok > > test2 > 31415 ok > > test3 > |significand| > 16777215 > > Here the sign is chabged only: > > test4 > |significand| > 16777215 > > test5 > 31438 ok > > test6 > |significand| > 16777215 > > > > My current understanding is the division is > cousing issues. The lost > of significant figures shall not be the case - see > the test 1: > > tmp = pi / (10000^5) > pi = tmp * 10000^6 (correct result 31415). > > The test 2: > > tmp = pi / 10000 / 10000 > pi = tmp * 10000^3 (correct result 31415). > > Te test 3: > > tmp = pi / 10000 / 10000 /10000 > pi = tmp * 10000^4 (error). > > The test4-6 are same as the above one, but with > minus sign at 10000. > So the result shall be 31415 (when ignoring the > sign). > > As you may see from previous test the f/ is > sensitive to signs of > the operands and gives unpecise results - see for > example test5 > result. > > Pito. > > > > > ----- PŮVODNÍ ZPRÁVA ----- > Od: "Leon N Maurer" <leon.mau...@gmail.com> > Komu: amforth-devel@lists.sourceforge.net > Předmět: Re: [Amforth-devel] Float testing - > small/large numbers > Datum: 29.8.2010 - 19:17:31 > > > I don't have my device handy so I can't test > > your > > > code. Could you be a little > > more clear about which ones failed, what the > > results are supposed to be, and > > what the results actually are? (When you write > > "the result shall be -31415", > > is that what it's supposed to be, what it > > actualy > > > is, or something else?) > > > > It looks like you're dividing and then > > multiplying > > > by very large powers of 10. > > I wouldn't be surprised if you loose some > > significant figures by doing this. > > -Leon > > > > ------------------------------------------------------------------------------ > > > > > > Sell apps to millions through the Intel(R) > > Atom(Tm) Developer Program > > Be part of this innovative community and reach > > millions of netbook users > > worldwide. Take advantage of special > > opportunities > > > to increase revenue and > > speed time-to-market. Join now, and jumpstart > > your > > > future. > > http://p.sf.net/sfu/intel-atom-d2d > > _______________________________________________ > > Amforth-devel mailing list > > Amforth-devel@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/amforth-devel > > > > > ------------------------------------------------------------------------------ > > Sell apps to millions through the Intel(R) > Atom(Tm) Developer Program > Be part of this innovative community and reach > millions of netbook users > worldwide. Take advantage of special opportunities > to increase revenue and > speed time-to-market. Join now, and jumpstart your > future. > http://p.sf.net/sfu/intel-atom-d2d > _______________________________________________ > Amforth-devel mailing list > Amforth-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/amforth-devel ------------------------------------------------------------------------------ Sell apps to millions through the Intel(R) Atom(Tm) Developer Program Be part of this innovative community and reach millions of netbook users worldwide. Take advantage of special opportunities to increase revenue and speed time-to-market. Join now, and jumpstart your future. http://p.sf.net/sfu/intel-atom-d2d _______________________________________________ Amforth-devel mailing list Amforth-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/amforth-devel
