================ StdFix Functions ================ .. include:: ../check.rst Standards and Goals ------------------- - stdfix.h is specified in the `ISO/IEC TR 18037:2008 `_, C extensions to support embedded processors . - Its `specifications `_. - Our goal is to implement a complete set of math functions for fixed point types, most of them are currently not included in the ISO/IEC TR 18037:2008 standard. Our math functions for fixed point types are modeled after the C99/C23 math functions for floating point types. --------------- 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 `_. 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 `_ using the default configuration of `typical desktop processor` in section A.3. Fixed-point Arithmetics ======================= The following functions are included in the ISO/IEC TR 18037:2008 standard. +---------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------+ | 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 | | |check| | | |check| | | |check| | | |check| | | |check| | | |check| | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ | bits\* | | | | | | | | | | | | | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ | \*bits | | | | | | | | | | | | | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ | countls | | | | | | | | | | | | | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ | divi | | | | | | | | | | | | | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ | idivi | | | | | | | | | | | | | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ | muli | | | | | | | | | | | | | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ | rdivi | | | | | | | | | | | | | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ | round | |check| | |check| | |check| | |check| | |check| | |check| | |check| | |check| | |check| | |check| | |check| | |check| | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ ================== ========= Type Generic Macro Available ================== ========= absfx countlsfx roundfx ================== ========= Higher math functions ===================== The following math functions are modeled after C99/C23 math functions for floating point types, but are not part of the ISO/IEC TR 18037:2008 spec. +---------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------+ | 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 | | | | | | | | |check| | | |check| | | | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ | log | | | | | | | | | | | | | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ | sin | | | | | | | | | | | | | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ | sqrt | |check| | | |check| | | |check| | | |check| | | |check| | | | | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ | tan | | | | | | | | | | | | | +---------------+----------------+-------------+---------------+------------+----------------+-------------+----------------+-------------+---------------+------------+----------------+-------------+ Conversion Functions ==================== The following conversion functions are included in the ISO/IEC TR 18037:2008 standard. +---------------+------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------+ | 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.