Go to file
Julius Werner 7a8a4ab1d8 lib: Unify log2() and related functions
This patch adds a few bit counting functions that are commonly needed
for certain register calculations. We previously had a log2()
implementation already, but it was awkwardly split between some C code
that's only available in ramstage and an optimized x86-specific
implementation in pre-RAM that prevented other archs from pulling it
into earlier stages.

Using __builtin_clz() as the baseline allows GCC to inline optimized
assembly for most archs (including CLZ on ARM/ARM64 and BSR on x86), and
to perform constant-folding if possible. What was previously named log2f
on pre-RAM x86 is now ffs, since that's the standard name for that
operation and I honestly don't have the slightest idea how it could've
ever ended up being called log2f (which in POSIX is 'binary(2) LOGarithm
with Float result, whereas the Find First Set operation has no direct
correlation to logarithms that I know of). Make ffs result 0-based
instead of the POSIX standard's 1-based since that is consistent with
clz, log2 and the former log2f, and generally closer to what you want
for most applications (a value that can directly be used as a shift to
reach the found bit). Call it __ffs() instead of ffs() to avoid problems
when importing code, since that's what Linux uses for the 0-based
operation.

CQ-DEPEND=CL:273023
BRANCH=None
BUG=None
TEST=Built on Big, Falco, Jerry, Oak and Urara. Compared old and new
log2() and __ffs() results on Falco for a bunch of test values.

Change-Id: I599209b342059e17b3130621edb6b6bbeae26876
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 3701a16ae944ecff9c54fa9a50d28015690fcb2f
Original-Change-Id: I60f7cf893792508188fa04d088401a8bca4b4af6
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/273008
Original-Reviewed-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-on: http://review.coreboot.org/10394
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
2015-06-05 13:18:55 +02:00
3rdparty 3rdparty/blobs: Move submodule marker forward 2015-05-13 22:55:50 +02:00
Documentation Remove address from GPLv2 headers 2015-05-21 20:50:25 +02:00
payloads lib: Unify log2() and related functions 2015-06-05 13:18:55 +02:00
src lib: Unify log2() and related functions 2015-06-05 13:18:55 +02:00
util build system: move more clang handling to xcompile 2015-06-04 20:02:01 +02:00
.gitignore gitignore: Have multiple crossgcc versions 2015-05-25 21:26:02 +02:00
.gitmodules 3rdparty/vboot: Add vboot 2015-05-05 22:49:34 +02:00
.gitreview add .gitreview 2012-11-01 23:13:39 +01:00
COPYING update license template. 2006-08-12 22:03:36 +00:00
MAINTAINERS MAINTAINERS: grab build system responsibility 2015-05-22 22:47:03 +02:00
Makefile build system: move more clang handling to xcompile 2015-06-04 20:02:01 +02:00
Makefile.inc board_id: Remove extra quotes. 2015-06-04 19:01:42 +02:00
README Update README with newer version of the text from the web page 2011-06-15 10:16:33 +02:00
toolchain.inc build system: move compiler runtime determination to xcompile 2015-06-04 20:01:45 +02:00

README

-------------------------------------------------------------------------------
coreboot README
-------------------------------------------------------------------------------

coreboot is a Free Software project aimed at replacing the proprietary BIOS
(firmware) found in most computers.  coreboot performs a little bit of
hardware initialization and then executes additional boot logic, called a
payload.

With the separation of hardware initialization and later boot logic,
coreboot can scale from specialized applications that run directly
firmware, run operating systems in flash, load custom
bootloaders, or implement firmware standards, like PC BIOS services or
UEFI. This allows for systems to only include the features necessary
in the target application, reducing the amount of code and flash space
required.

coreboot was formerly known as LinuxBIOS.


Payloads
--------

After the basic initialization of the hardware has been performed, any
desired "payload" can be started by coreboot.

See http://www.coreboot.org/Payloads for a list of supported payloads.


Supported Hardware
------------------

coreboot supports a wide range of chipsets, devices, and mainboards.

For details please consult:

 * http://www.coreboot.org/Supported_Motherboards
 * http://www.coreboot.org/Supported_Chipsets_and_Devices


Build Requirements
------------------

 * gcc / g++
 * make

Optional:

 * doxygen (for generating/viewing documentation)
 * iasl (for targets with ACPI support)
 * gdb (for better debugging facilities on some targets)
 * ncurses (for 'make menuconfig')
 * flex and bison (for regenerating parsers)


Building coreboot
-----------------

Please consult http://www.coreboot.org/Build_HOWTO for details.


Testing coreboot Without Modifying Your Hardware
------------------------------------------------

If you want to test coreboot without any risks before you really decide
to use it on your hardware, you can use the QEMU system emulator to run
coreboot virtually in QEMU.

Please see http://www.coreboot.org/QEMU for details.


Website and Mailing List
------------------------

Further details on the project, a FAQ, many HOWTOs, news, development
guidelines and more can be found on the coreboot website:

  http://www.coreboot.org

You can contact us directly on the coreboot mailing list:

  http://www.coreboot.org/Mailinglist


Copyright and License
---------------------

The copyright on coreboot is owned by quite a large number of individual
developers and companies. Please check the individual source files for details.

coreboot is licensed under the terms of the GNU General Public License (GPL).
Some files are licensed under the "GPL (version 2, or any later version)",
and some files are licensed under the "GPL, version 2". For some parts, which
were derived from other projects, other (GPL-compatible) licenses may apply.
Please check the individual source files for details.

This makes the resulting coreboot images licensed under the GPL, version 2.