On Fri, Dec 27, 2002 at 10:47:08 -0500, Lukas Geyer wrote: > The funny thing about this is that the result is _exactly_ sin(x) > instead of cos(x).
Yes, I didn't notice that. > Furthermore, it seems to be a special case, as slightly changing x > gives correct results. Yes, this is a special case (difficult to round exactly). And the problem occurs only in a small interval (something like 0.80 to 0.83). According to one of my test programs: Error: cos (line 33) [arg.] x = 0.80190127184058835 [corr] y = 0.69534156199418473 [libm] z = 0.71867942238767868 Error: cos (line 34) [arg.] x = 0.8107741500588278 [corr] y = 0.68893751943804493 [libm] z = 0.72482073253360613 Error: cos (line 35) [arg.] x = 0.81808070960270574 [corr] y = 0.68362323105565981 [libm] z = 0.72983510326718326 Error: cos (line 36) [arg.] x = 0.81909979079003903 [corr] y = 0.6828791149804222 [libm] z = 0.73053139174408888 Error: cos (line 37) [arg.] x = 0.82926610298753134 [corr] y = 0.67541714390565444 [libm] z = 0.73743588312363018 No problem before line 33 and after line 37. The errors correspond to the arguments (in binary): 1.1001101010010010110011011011001001011010001011100001E-1 1.1001111100011101110010100001010111100011110001001111E-1 1.1010001011011011011110011000101001110110110101010001E-1 1.1010001101100001000011000011101100110101000100101110E-1 1.1010100010010101100100010001000000000110100011111011E-1 But no problem for 1.1001100011001001100011001100000101110101100111011100E-1 and 1.1011110111000011110110110001101101010000010000010001E-1 for instance. Regards, -- Vincent Lef�vre <[EMAIL PROTECTED]> - Web: <http://www.vinc17.org/> - 100% validated (X)HTML - Acorn Risc PC, Yellow Pig 17, Championnat International des Jeux Math�matiques et Logiques, TETRHEX, etc. Work: CR INRIA - computer arithmetic / SPACES project at LORIA
