freebsd kernel with SKQ
d6cdac5f7a
to floats (mainly i386's). All errors of more than 1 ulp for float precision trig functions were supposed to have been fixed; however, compiling with gcc -O2 uncovered 18250 more such errors for cosf(), with a maximum error of 1.409 ulps. Use essentially the same fix as in rev.1.8 of k_rem_pio2f.c (access a non-volatile variable as a volatile). Here the -O1 case apparently worked because the variable is in a 2-element array and it takes -O2 to mess up such a variable by putting it in a register. The maximum error for cosf() on i386 with gcc -O2 is now 0.5467 (it is still 0.5650 with gcc -O1). This shows that -O2 still causes some extra precision, but the extra precision is now good. Extra precision is harmful mainly for implementing extra precision in software. We want to represent x+y as w+r where both "+" operations are in infinite precision and r is tiny compared with w. There is a standard algorithm for this (Knuth (1981) 4.2.2 Theorem C), and fdlibm uses this routinely, but the algorithm requires w and r to have the same precision as x and y. w is just x+y (calculated in the same finite precision as x and y), and r is a tiny correction term. The i386 gcc bugs tend to give extra precision in w, and then using this extra precision in the calculation of r results in the correction mostly staying in w and being missing from r. There still tends to be no problem if the result is a simple expression involving w and r -- modulo spills, w keeps its extra precision and r remains the right correction for this wrong w. However, here we want to pass w and r to extern functions. Extra precision is not retained in function args, so w gets fixed up, but the change to the tiny r is tinier, so r almost remains as a wrong correction for the right w. |
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| bin | ||
| contrib | ||
| 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