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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)
Fixed point extension standard: https://standards.iso.org/ittf/PubliclyAvailableStandards/c051126_ISO_IEC_TR_18037_2008.zip
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11 files changed

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‎libc/cmake/modules/CheckCompilerFeatures.cmake

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# Compiler features definition and flags
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# ------------------------------------------------------------------------------
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# Initialize ALL_COMPILER_FEATURES as empty list.
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set(ALL_COMPILER_FEATURES "float128")
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set(ALL_COMPILER_FEATURES "float128" "fixed_point")
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# Making sure ALL_COMPILER_FEATURES is sorted.
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list(SORT ALL_COMPILER_FEATURES)
@@ -42,16 +41,23 @@ set(AVAILABLE_COMPILER_FEATURES "")
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# Try compile a C file to check if flag is supported.
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set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
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foreach(feature IN LISTS ALL_COMPILER_FEATURES)
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set(compile_options ${LIBC_COMPILE_OPTIONS_NATIVE})
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if(${feature} STREQUAL "fixed_point")
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list(APPEND compile_options "-ffixed-point")
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endif()
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try_compile(
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has_feature
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${CMAKE_CURRENT_BINARY_DIR}/compiler_features
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SOURCES ${LIBC_SOURCE_DIR}/cmake/modules/compiler_features/check_${feature}.cpp
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COMPILE_DEFINITIONS -I${LIBC_SOURCE_DIR} ${LIBC_COMPILE_OPTIONS_NATIVE}
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COMPILE_DEFINITIONS -I${LIBC_SOURCE_DIR} ${compile_options}
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)
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if(has_feature)
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list(APPEND AVAILABLE_COMPILER_FEATURES ${feature})
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if(${feature} STREQUAL "float128")
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set(LIBC_COMPILER_HAS_FLOAT128 TRUE)
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elseif(${feature} STREQUAL "fixed_point")
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set(LIBC_COMPILER_HAS_FIXED_POINT TRUE)
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endif()
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endif()
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endforeach()

‎libc/cmake/modules/compiler_features/check_fixed_point.cpp

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#include "include/llvm-libc-macross/stdfix_macros.h"
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#ifndef LIBC_COMPILER_HAS_FIXED_POINT
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#error unsupported
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#endif

‎libc/config/linux/api.td

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@@ -6,6 +6,7 @@ include "spec/linux.td"
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include "spec/gnu_ext.td"
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include "spec/bsd_ext.td"
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include "spec/llvm_libc_ext.td"
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include "spec/stdc_ext.td"
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def AssertMacro : MacroDef<"assert"> {
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let Defn = [{

‎libc/config/linux/x86_64/headers.txt

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@@ -16,6 +16,7 @@ set(TARGET_PUBLIC_HEADERS
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libc.include.spawn
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libc.include.setjmp
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libc.include.stdbit
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libc.include.stdfix
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libc.include.stdio
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libc.include.stdlib
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libc.include.string

‎libc/docs/math/index.rst

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:hidden:
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log.rst
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stdfix.rst
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.. contents:: Table of Contents
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* :doc:`log`
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Fixed-point Arithmetics
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=======================
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* :doc:`stdfix`
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References
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==========
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‎libc/docs/math/stdfix.rst

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================
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StdFix Functions
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================
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.. include:: ../check.rst
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Standards
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---------
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- stdfix.h is specified in the `ISO/IEC TR 18037:2008 <https://www.iso.org/standard/51126.html>`_,
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C extensions to support embedded processors .
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- Its `specifications <https://standards.iso.org/ittf/PubliclyAvailableStandards/c051126_ISO_IEC_TR_18037_2008.zip>`_.
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---------------
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Source location
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---------------
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- The main source for fixed-point functions is located at:
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``libc/src/stdfix`` with subdirectories for internal implementations.
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---------------------
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Implementation Status
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---------------------
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Requirements
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============
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- In order to build LLVM libc to support fixed-point arithmetics, we need the
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compiler to support the basic fixed-point types `_Fract` and `_Accum` in
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C++.
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- For the users to be able to use the generated headers, their compiler needs
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to support `_Fract` and `_Accum` types in C or C++.
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- This compiler support is checked at the beginning of
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`libc/include/llvm-libc-macros/stdfix-macros.h <https://github.com/llvm/llvm-project/tree/main/libc/include/llvm-libc-macros/stdfix-macros.h>`_.
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Predefined Macros
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=================
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- We use the macro `LIBC_COMPILER_HAS_FIXED_POINT` to specify whether the
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compiler support the fixed-point types.
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- Other predefined precision macros specified in section 7.18a.3 are defined
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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>`_
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using the default configuration of `typical desktop processor` in section
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A.3.
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Fixed-point Arithmetics
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=======================
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+---------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------+
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| Function Name | _Fract (r) | _Accum (k) |
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| +------------------------------+----------------------------+------------------------------+------------------------------+----------------------------+------------------------------+
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| | short (hr) | _ (r) | long (lr) | short (hk) | _ (k) | long (lk) |
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| +----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| | unsigned (uhr) | signed (hr) | unsigned (ur) | signed (r) | unsigned (ulr) | signed (lr) | unsigned (uhk) | signed (hk) | unsigned (uk) | signed (k) | unsigned (ulk) | signed (lk) |
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+===============+================+=============+===============+============+================+=============+================+=============+===============+============+================+=============+
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| abs | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| bits\* | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| \*bits | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| countls | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| divi | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| idivi | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| muli | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| rdivi | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| round | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| sqrt | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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================== =========
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Type Generic Macro Available
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================== =========
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absfx
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countlsfx
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roundfx
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================== =========
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Higher math functions
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=====================
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+---------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------+
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| Function Name | _Fract (r) | _Accum (k) |
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| +------------------------------+----------------------------+------------------------------+------------------------------+----------------------------+------------------------------+
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| | short (hr) | _ (r) | long (lr) | short (hk) | _ (k) | long (lk) |
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| +----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| | unsigned (uhr) | signed (hr) | unsigned (ur) | signed (r) | unsigned (ulr) | signed (lr) | unsigned (uhk) | signed (hk) | unsigned (uk) | signed (k) | unsigned (ulk) | signed (lk) |
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+===============+================+=============+===============+============+================+=============+================+=============+===============+============+================+=============+
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| cos | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| exp | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| log | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| sin | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| tan | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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Conversion Functions
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====================
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+---------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------+
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| Function Name | _Fract (r) | _Accum (k) |
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| +------------------------------+----------------------------+------------------------------+------------------------------+----------------------------+------------------------------+
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| | short (hr) | _ (r) | long (lr) | short (hk) | _ (k) | long (lk) |
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| +----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| | unsigned (uhr) | signed (hr) | unsigned (ur) | signed (r) | unsigned (ulr) | signed (lr) | unsigned (uhk) | signed (hk) | unsigned (uk) | signed (k) | unsigned (ulk) | signed (lk) |
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+===============+================+=============+===============+============+================+=============+================+=============+===============+============+================+=============+
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| fprintf | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| fscanf | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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| strtofx | | | | | | | | | | | | |
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+---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+
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Warnings
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========
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This is currently a work-in-progress, its headers, macros, and ABI are still unstable, and might be modified.

‎libc/include/CMakeLists.txt

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@@ -104,6 +104,14 @@ add_gen_header(
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.llvm-libc-types.float128
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)
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107+
add_gen_header(
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stdfix
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DEF_FILE stdfix.h.def
110+
GEN_HDR stdfix.h
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DEPENDS
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.llvm-libc-macros.stdfix_macros
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)
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# TODO: This should be conditional on POSIX networking being included.
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file(MAKE_DIRECTORY ${LIBC_INCLUDE_DIR}/arpa)
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‎libc/include/llvm-libc-macros/CMakeLists.txt

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@@ -227,3 +227,9 @@ add_macro_header(
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HDR
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inttypes-macros.h
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)
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add_macro_header(
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stdfix_macros
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HDR
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stdfix-macros.h
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)

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