The overflow check was relying on undefined behaviour as it was using the result of the multiplication to do the check, and once the overflow has already happened, any operation on the result is undefined behaviour.
Some extra checks that exercise code paths related to this are also added.
The standard math library (libm) may follow IEEE-754 recommendation to
include an implementation of sinPi(), i.e. sinPi(x):=sin(pi*x).
And this triggers a name clash, found by FreeBSD developer
Steve Kargl, who worken on putting sinpi into libm used on FreeBSD
(it has to be named "sinpi", not "sinPi", cf. e.g.
https://en.cppreference.com/w/c/experimental/fpext4).
Use the fast call convention for math functions atan2(),
copysign(), hypot() and remainder() and inline unpacking
arguments. This sped up them by 1.3--2.5 times.
The *max* value is no longer treated as a special case in the main loop. Besides making the main loop simpler and branchless, this also lets us relax the input restriction of *vec* to contain only non-negative values.
* Add Py_UNREACHABLE() as an alias to abort().
* Use Py_UNREACHABLE() instead of assert(0)
* Convert more unreachable code to use Py_UNREACHABLE()
* Document Py_UNREACHABLE() and a few other macros.
* Implement math.remainder.
* Fix markup for arguments; use double spaces after period.
* Mark up function reference in what's new entry.
* Add comment explaining the calculation in the final branch.
* Fix out-of-order entry in whatsnew.
* Add comment explaining why it's good enough to compare m with c, in spite of possible rounding error.
