freebsd kernel with SKQ
16638b5585
A single polynomial approximation for tan(x) works in infinite precision up to |x| < pi/2, but in finite precision, to restrict the accumulated roundoff error to < 1 ulp, |x| must be restricted to less than about sqrt(0.5/((1.5+1.5)/3)) ~= 0.707. We restricted it a bit more to give a safety margin including some slop for optimizations. Now that we use double precision for the calculations, the accumulated roundoff error is in double-precision ulps so it can easily be made almost 2**29 times smaller than a single-precision ulp. Near x = pi/4 its maximum is about 0.5+(1.5+1.5)*x**2/3 ~= 1.117 double-precision ulps. The minimax polynomial needs to be different to work for the larger interval. I didn't increase its degree the old degree is just large enough to keep the final error less than 1 ulp and increasing the degree would be a pessimization. The maximum error is now ~0.80 ulps instead of ~0.53 ulps. The speedup from this optimization for uniformly distributed args in [-2pi, 2pi] is 28-43% on athlons, depending on how badly gcc selected and scheduled the instructions in the old version. The old version has some int-to-float conversions that are apparently difficult to schedule well, but gcc-3.3 somehow did everything ~10 cycles or ~10% faster than gcc-3.4, with the difference especially large on AXPs. On A64s, the problem seems to be related to documented penalties for moving single precision data to undead xmm registers. With this version, the speed is cycles is almost independent of the athlon and gcc version despite the large differences in instruction selection to use the FPU on AXPs and SSE on A64s. |
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| crypto | ||
| etc | ||
| games | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| lib | ||
| libexec | ||
| release | ||
| rescue | ||
| sbin | ||
| secure | ||
| share | ||
| sys | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| COPYRIGHT | ||
| LOCKS | ||
| MAINTAINERS | ||
| Makefile | ||
| Makefile.inc1 | ||
| ObsoleteFiles.inc | ||
| README | ||
| UPDATING | ||
This is the top level of the FreeBSD source directory. This file was last revised on: $FreeBSD$ For copyright information, please see the file COPYRIGHT in this directory (additional copyright information also exists for some sources in this tree - please see the specific source directories for more information). The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree, the most commonly used one being ``world'', which rebuilds and installs everything in the FreeBSD system from the source tree except the kernel, the kernel-modules and the contents of /etc. The ``buildkernel'' and ``installkernel'' targets build and install the kernel and the modules (see below). Please see the top of the Makefile in this directory for more information on the standard build targets and compile-time flags. Building a kernel is a somewhat more involved process, documentation for which can be found at: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html And in the config(8) man page. Note: If you want to build and install the kernel with the ``buildkernel'' and ``installkernel'' targets, you might need to build world before. More information is available in the handbook. The sample kernel configuration files reside in the sys/<arch>/conf sub-directory (assuming that you've installed the kernel sources), the file named GENERIC being the one used to build your initial installation kernel. The file NOTES contains entries and documentation for all possible devices, not just those commonly used. It is the successor of the ancient LINT file, but in contrast to LINT, it is not buildable as a kernel but a pure reference and documentation file. Source Roadmap: --------------- bin System/user commands. contrib Packages contributed by 3rd parties. crypto Cryptography stuff (see crypto/README). etc Template files for /etc. games Amusements. gnu Various commands and libraries under the GNU Public License. Please see gnu/COPYING* for more information. include System include files. kerberos5 Kerberos5 (Heimdal) package. lib System libraries. libexec System daemons. release Release building Makefile & associated tools. sbin System commands. secure Cryptographic libraries and commands. share Shared resources. sys Kernel sources. tools Utilities for regression testing and miscellaneous tasks. usr.bin User commands. usr.sbin System administration commands. For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/synching.html