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[libc][stdfix] Generate stdfix.h header with fixed point precision macros according to ISO/IEC TR 18037:2008 standard, and add fixed point type support detection. #81255

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Merged
merged 8 commits into from
Feb 13, 2024
Merged

[libc][stdfix] Generate stdfix.h header with fixed point precision macros according to ISO/IEC TR 18037:2008 standard, and add fixed point type support detection. #81255

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61cc872
[libc][stdfix] Generate stdfix.h header with fixed point precision ma…
lntue Feb 9, 2024
a8ebbc1
Move to stdc_ext.td and remove test file.
lntue Feb 9, 2024
9fdc037
Address comments.
lntue Feb 9, 2024
1eceaf6
Address comments.
lntue Feb 9, 2024
dd25d98
Add documentations for stdfix.
lntue Feb 12, 2024
8d2527f
Fix docs.
lntue Feb 12, 2024
e2a9af5
Update the standard name and links.
lntue Feb 13, 2024
fd42032
Fix format.
lntue Feb 13, 2024
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12 changes: 9 additions & 3 deletions libc/cmake/modules/CheckCompilerFeatures.cmake
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Expand Up @@ -2,8 +2,7 @@
# Compiler features definition and flags
# ------------------------------------------------------------------------------

# Initialize ALL_COMPILER_FEATURES as empty list.
set(ALL_COMPILER_FEATURES "float128")
set(ALL_COMPILER_FEATURES "float128" "fixed_point")

# Making sure ALL_COMPILER_FEATURES is sorted.
list(SORT ALL_COMPILER_FEATURES)
Expand Down Expand Up @@ -42,16 +41,23 @@ set(AVAILABLE_COMPILER_FEATURES "")
# Try compile a C file to check if flag is supported.
set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
foreach(feature IN LISTS ALL_COMPILER_FEATURES)
set(compile_options ${LIBC_COMPILE_OPTIONS_NATIVE})
if(${feature} STREQUAL "fixed_point")
list(APPEND compile_options "-ffixed-point")
endif()

try_compile(
has_feature
${CMAKE_CURRENT_BINARY_DIR}/compiler_features
SOURCES ${LIBC_SOURCE_DIR}/cmake/modules/compiler_features/check_${feature}.cpp
COMPILE_DEFINITIONS -I${LIBC_SOURCE_DIR} ${LIBC_COMPILE_OPTIONS_NATIVE}
COMPILE_DEFINITIONS -I${LIBC_SOURCE_DIR} ${compile_options}
)
if(has_feature)
list(APPEND AVAILABLE_COMPILER_FEATURES ${feature})
if(${feature} STREQUAL "float128")
set(LIBC_COMPILER_HAS_FLOAT128 TRUE)
elseif(${feature} STREQUAL "fixed_point")
set(LIBC_COMPILER_HAS_FIXED_POINT TRUE)
endif()
endif()
endforeach()
Expand Down
5 changes: 5 additions & 0 deletions libc/cmake/modules/compiler_features/check_fixed_point.cpp
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@@ -0,0 +1,5 @@
#include "include/llvm-libc-macross/stdfix_macros.h"

#ifndef LIBC_COMPILER_HAS_FIXED_POINT
#error unsupported
#endif
1 change: 1 addition & 0 deletions libc/config/linux/api.td
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Expand Up @@ -6,6 +6,7 @@ include "spec/linux.td"
include "spec/gnu_ext.td"
include "spec/bsd_ext.td"
include "spec/llvm_libc_ext.td"
include "spec/stdc_ext.td"

def AssertMacro : MacroDef<"assert"> {
let Defn = [{
Expand Down
1 change: 1 addition & 0 deletions libc/config/linux/x86_64/headers.txt
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Expand Up @@ -16,6 +16,7 @@ set(TARGET_PUBLIC_HEADERS
libc.include.spawn
libc.include.setjmp
libc.include.stdbit
libc.include.stdfix
libc.include.stdio
libc.include.stdlib
libc.include.string
Expand Down
6 changes: 6 additions & 0 deletions libc/docs/math/index.rst
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Expand Up @@ -16,6 +16,7 @@ Math Functions
:hidden:

log.rst
stdfix.rst


.. contents:: Table of Contents
Expand Down Expand Up @@ -607,6 +608,11 @@ Algorithms + Implementation Details

* :doc:`log`

Fixed-point Arithmetics
=======================

* :doc:`stdfix`

References
==========

Expand Down
136 changes: 136 additions & 0 deletions libc/docs/math/stdfix.rst
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@@ -0,0 +1,136 @@
================
StdFix Functions
================

.. include:: ../check.rst

Standards
---------

- stdfix.h is specified in the `ISO/IEC TR 18037:2008 <https://www.iso.org/standard/51126.html>`_,
C extensions to support embedded processors .

- Its `specifications <https://standards.iso.org/ittf/PubliclyAvailableStandards/c051126_ISO_IEC_TR_18037_2008.zip>`_.

---------------
Source location
---------------

- The main source for fixed-point functions is located at:
``libc/src/stdfix`` with subdirectories for internal implementations.

---------------------
Implementation Status
---------------------

Requirements
============

- In order to build LLVM libc to support fixed-point arithmetics, we need the
compiler to support the basic fixed-point types `_Fract` and `_Accum` in
C++.

- For the users to be able to use the generated headers, their compiler needs
to support `_Fract` and `_Accum` types in C or C++.

- This compiler support is checked at the beginning of
`libc/include/llvm-libc-macros/stdfix-macros.h <https://github.com/llvm/llvm-project/tree/main/libc/include/llvm-libc-macros/stdfix-macros.h>`_.



Predefined Macros
=================

- We use the macro `LIBC_COMPILER_HAS_FIXED_POINT` to specify whether the
compiler support the fixed-point types.

- Other predefined precision macros specified in section 7.18a.3 are defined
in `libc/include/llvm-libc-macros/stdfix-macros.h <https://github.com/llvm/llvm-project/tree/main/libc/include/llvm-libc-macros/stdfix-macros.h>`_
using the default configuration of `typical desktop processor` in section
A.3.


Fixed-point Arithmetics
=======================

+---------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------+
| Function Name | _Fract (r) | _Accum (k) |
| +------------------------------+----------------------------+------------------------------+------------------------------+----------------------------+------------------------------+
| | short (hr) | _ (r) | long (lr) | short (hk) | _ (k) | long (lk) |
| +----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| | unsigned (uhr) | signed (hr) | unsigned (ur) | signed (r) | unsigned (ulr) | signed (lr) | unsigned (uhk) | signed (hk) | unsigned (uk) | signed (k) | unsigned (ulk) | signed (lk) |
+===============+================+=============+===============+============+================+=============+================+=============+===============+============+================+=============+
| abs | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| bits\* | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| \*bits | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| countls | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| divi | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| idivi | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| muli | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| rdivi | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| round | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| sqrt | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+

================== =========
Type Generic Macro Available
================== =========
absfx
countlsfx
roundfx
================== =========


Higher math functions
=====================

+---------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------+
| Function Name | _Fract (r) | _Accum (k) |
| +------------------------------+----------------------------+------------------------------+------------------------------+----------------------------+------------------------------+
| | short (hr) | _ (r) | long (lr) | short (hk) | _ (k) | long (lk) |
| +----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| | unsigned (uhr) | signed (hr) | unsigned (ur) | signed (r) | unsigned (ulr) | signed (lr) | unsigned (uhk) | signed (hk) | unsigned (uk) | signed (k) | unsigned (ulk) | signed (lk) |
+===============+================+=============+===============+============+================+=============+================+=============+===============+============+================+=============+
| cos | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| exp | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| log | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| sin | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| tan | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+


Conversion Functions
====================

+---------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------+
| Function Name | _Fract (r) | _Accum (k) |
| +------------------------------+----------------------------+------------------------------+------------------------------+----------------------------+------------------------------+
| | short (hr) | _ (r) | long (lr) | short (hk) | _ (k) | long (lk) |
| +----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| | unsigned (uhr) | signed (hr) | unsigned (ur) | signed (r) | unsigned (ulr) | signed (lr) | unsigned (uhk) | signed (hk) | unsigned (uk) | signed (k) | unsigned (ulk) | signed (lk) |
+===============+================+=============+===============+============+================+=============+================+=============+===============+============+================+=============+
| fprintf | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| fscanf | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
| strtofx | | | | | | | | | | | | |
+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+


Warnings
========

This is currently a work-in-progress, its headers, macros, and ABI are still unstable, and might be modified.
8 changes: 8 additions & 0 deletions libc/include/CMakeLists.txt
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Expand Up @@ -104,6 +104,14 @@ add_gen_header(
.llvm-libc-types.float128
)

add_gen_header(
stdfix
DEF_FILE stdfix.h.def
GEN_HDR stdfix.h
DEPENDS
.llvm-libc-macros.stdfix_macros
)

# TODO: This should be conditional on POSIX networking being included.
file(MAKE_DIRECTORY ${LIBC_INCLUDE_DIR}/arpa)

Expand Down
6 changes: 6 additions & 0 deletions libc/include/llvm-libc-macros/CMakeLists.txt
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Expand Up @@ -227,3 +227,9 @@ add_macro_header(
HDR
inttypes-macros.h
)

add_macro_header(
stdfix_macros
HDR
stdfix-macros.h
)
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