The implementation of the <misc/math_extras.h> functions will use the
portable C code when PORTABLE_MISC_MATH_EXTRAS is defined before
including the header.
Use this feature macro to make sure that the unit test always tests the
portable functions in addition to the ones using builtins for the
current compiler.
Signed-off-by: Jakob Olesen <jolesen@fb.com>
Add a <misc/math_extras.h> header file with portable implementations of
a number of commonly used math and bit counting operations that are not
available in the C programming language.
The math_extras functions fall into two groups:
1. Unsigned integer arithmetic with overflow detection. Addition and
multiplication are provides for the u32_t, u64_t, and size_t types.
This commit doesn't include subtraction and division, and there are
no signed operations. These could be added later if there is a need.
2. Bit-counting operations like clz, ctz, and ffs. These are provided
for u32_t and u64_t only. I don't see a need for size_t operations,
but they could be added if needed.
A follow-on commit will add more efficient implementations using
compiler builtins for those compilers that support it.
Another commit will replace other uses of "naked" compiler builtins with
calls to these functions.
Signed-off-by: Jakob Olesen <jolesen@fb.com>
