mirror of
https://github.com/zephyrproject-rtos/zephyr
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822dfbd012
The _ldiv5() is an optimized divide-by-5 function that is smaller and
faster than the generic libgcc implementation.
Yet it can be made even smaller and faster with this replacement
implementation based on a reciprocal multiplication plus some tricks.
For example, here's the assembly from the original code on ARM:
_ldiv5:
ldr r3, [r0]
movw ip, #52429
ldr r1, [r0, #4]
movt ip, 52428
adds r3, r3, #2
push {r4, r5, r6, r7, lr}
mov lr, #0
adc r1, r1, lr
adds r2, lr, lr
umull r7, r6, ip, r1
lsr r6, r6, #2
adc r7, r6, r6
adds r2, r2, r2
adc r7, r7, r7
adds r2, r2, lr
adc r7, r7, r6
subs r3, r3, r2
sbc r7, r1, r7
lsr r2, r3, #3
orr r2, r2, r7, lsl #29
umull r2, r1, ip, r2
lsr r2, r1, #2
lsr r7, r1, #31
lsl r1, r2, #3
adds r4, lr, r1
adc r5, r6, r7
adds r2, r1, r1
adds r2, r2, r2
adds r2, r2, r1
subs r2, r3, r2
umull r3, r2, ip, r2
lsr r2, r2, #2
adds r4, r4, r2
adc r5, r5, #0
strd r4, [r0]
pop {r4, r5, r6, r7, pc}
And here's the resulting assembly with this commit applied:
_ldiv5:
push {r4, r5, r6, r7}
movw r4, #13107
ldr r6, [r0]
movt r4, 13107
ldr r1, [r0, #4]
mov r3, #0
umull r6, r7, r6, r4
add r2, r4, r4, lsl #1
umull r4, r5, r1, r4
adds r1, r6, r2
adc r2, r7, r2
adds ip, r6, r4
adc r1, r7, r5
adds r2, ip, r2
adc r2, r1, r3
adds r2, r4, r2
adc r3, r5, r3
strd r2, [r0]
pop {r4, r5, r6, r7}
bx lr
So we're down to 20 instructions from 36 initially, with only 2 umull
instructions instead of 3, and slightly smaller stack footprint.
Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
|
||
|---|---|---|
| .buildkite | ||
| .github | ||
| .known-issues | ||
| arch | ||
| boards | ||
| cmake | ||
| doc | ||
| drivers | ||
| dts | ||
| include | ||
| kernel | ||
| lib | ||
| misc | ||
| modules | ||
| samples | ||
| scripts | ||
| share | ||
| soc | ||
| subsys | ||
| tests | ||
| .checkpatch.conf | ||
| .clang-format | ||
| .codecov.yml | ||
| .editorconfig | ||
| .gitattributes | ||
| .gitignore | ||
| .gitlint | ||
| .mailmap | ||
| .uncrustify.cfg | ||
| CMakeLists.txt | ||
| CODE_OF_CONDUCT.md | ||
| CODEOWNERS | ||
| CONTRIBUTING.rst | ||
| Kconfig | ||
| Kconfig.zephyr | ||
| LICENSE | ||
| MAINTAINERS.yml | ||
| Makefile | ||
| README.rst | ||
| VERSION | ||
| version.h.in | ||
| west.yml | ||
| zephyr-env.cmd | ||
| zephyr-env.sh | ||
.. raw:: html
<a href="https://www.zephyrproject.org">
<p align="center">
<img src="doc/images/Zephyr-Project.png">
</p>
</a>
<a href="https://bestpractices.coreinfrastructure.org/projects/74"><img
src="https://bestpractices.coreinfrastructure.org/projects/74/badge"></a>
<a href="https://buildkite.com/zephyr/zephyr">
<img
src="https://badge.buildkite.com/f5bd0dc88306cee17c9b38e78d11bb74a6291e3f40e7d13f31.svg?branch=master"></a>
The Zephyr Project is a scalable real-time operating system (RTOS) supporting
multiple hardware architectures, optimized for resource constrained devices,
and built with security in mind.
The Zephyr OS is based on a small-footprint kernel designed for use on
resource-constrained systems: from simple embedded environmental sensors and
LED wearables to sophisticated smart watches and IoT wireless gateways.
The Zephyr kernel supports multiple architectures, including ARM Cortex-M,
Intel x86, ARC, Nios II, Tensilica Xtensa, and RISC-V, and a large number of
`supported boards`_.
.. below included in doc/introduction/introduction.rst
.. start_include_here
Getting Started
***************
Welcome to Zephyr! See the `Introduction to Zephyr`_ for a high-level overview,
and the documentation's `Getting Started Guide`_ to start developing.
Community Support
*****************
Community support is provided via mailing lists and Slack; see the Resources
below for details.
.. _project-resources:
Resources
*********
Here's a quick summary of resources to help you find your way around:
* **Help**: `Asking for Help Tips`_
* **Documentation**: http://docs.zephyrproject.org (`Getting Started Guide`_)
* **Source Code**: https://github.com/zephyrproject-rtos/zephyr is the main
repository; https://elixir.bootlin.com/zephyr/latest/source contains a
searchable index
* **Releases**: https://github.com/zephyrproject-rtos/zephyr/releases
* **Samples and example code**: see `Sample and Demo Code Examples`_
* **Mailing Lists**: users@lists.zephyrproject.org and
devel@lists.zephyrproject.org are the main user and developer mailing lists,
respectively. You can join the developer's list and search its archives at
`Zephyr Development mailing list`_. The other `Zephyr mailing list
subgroups`_ have their own archives and sign-up pages.
* **Nightly CI Build Status**: https://lists.zephyrproject.org/g/builds
The builds@lists.zephyrproject.org mailing list archives the CI
(shippable) nightly build results.
* **Chat**: Zephyr's Slack workspace is https://zephyrproject.slack.com. Use
this `Slack Invite`_ to register.
* **Contributing**: see the `Contribution Guide`_
* **Wiki**: `Zephyr GitHub wiki`_
* **Issues**: https://github.com/zephyrproject-rtos/zephyr/issues
* **Security Issues**: Email vulnerabilities@zephyrproject.org to report
security issues; also see our `Security`_ documentation. Security issues are
tracked separately at https://zephyrprojectsec.atlassian.net.
* **Zephyr Project Website**: https://zephyrproject.org
.. _Slack Invite: https://tinyurl.com/y5glwylp
.. _supported boards: http://docs.zephyrproject.org/latest/boards/index.html
.. _Zephyr Documentation: http://docs.zephyrproject.org
.. _Introduction to Zephyr: http://docs.zephyrproject.org/latest/introduction/index.html
.. _Getting Started Guide: http://docs.zephyrproject.org/latest/getting_started/index.html
.. _Contribution Guide: http://docs.zephyrproject.org/latest/contribute/index.html
.. _Zephyr GitHub wiki: https://github.com/zephyrproject-rtos/zephyr/wiki
.. _Zephyr Development mailing list: https://lists.zephyrproject.org/g/devel
.. _Zephyr mailing list subgroups: https://lists.zephyrproject.org/g/main/subgroups
.. _Sample and Demo Code Examples: http://docs.zephyrproject.org/latest/samples/index.html
.. _Security: http://docs.zephyrproject.org/latest/security/index.html
.. _Asking for Help Tips: https://docs.zephyrproject.org/latest/guides/getting-help.html