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From: | Peter Avalos <pavalos@xxxxxxxxxxxxxxxxxxxxxxx> |

Date: | Tue, 3 Jul 2007 11:51:45 -0700 (PDT) |

pavalos 2007/07/03 11:51:45 PDT DragonFly src repository Modified files: lib/libm/src e_lgammaf_r.c Log: From FreeBSD's log: Log: Fixed about 50 million errors of infinity ulps and about 3 million errors of between 1.0 and 1.8509 ulps for lgammaf(x) with x between -2**-21 and -2**-70. As usual, the cutoff for tiny args was not correctly translated to float precision. It was 2**-70 but 2**-21 works. Not as usual, having a too-small threshold was worse than a pessimization. It was just a pessimization for (positive) args between 2**-70 and 2**-21, but for the first ~50 million (negative) args below -2**-70, the general code overflowed and gave a result of infinity instead of correct (finite) results near 70*log(2). For the remaining ~361 million negative args above -2**21, the general code gave almost-acceptable errors (lgamma[f]() is not very accurate in general) but the pessimization was larger than for misclassified tiny positive args. Now the max error for lgammaf(x) with |x| < 2**-21 is 0.7885 ulps, and speed and accuracy are almost the same for positive and negative args in this range. The maximum error overall is still infinity ulps. A cutoff of 2**-70 is probably wastefully small for the double precision case. Smaller cutoffs can be used to reduce the max error to nearly 0.5 ulps for tiny args, but this is useless since the general algrorithm for nearly-tiny args is not nearly that accurate -- it has a max error of about 1 ulp. Obtained-from: FreeBSD Revision Changes Path 1.2 +1 -1 src/lib/libm/src/e_lgammaf_r.c http://www.dragonflybsd.org/cvsweb/src/lib/libm/src/e_lgammaf_r.c.diff?r1=1.1&r2=1.2&f=u

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