Document round-off error in `.mod_euc()`-method, see issue #50179
Due to a round-off error the method `.mod_euc()` of both `f32` and `f64` can produce mathematical invalid outputs. If `self` in magnitude is much small than the modulus `rhs` and negative, `self + rhs` in the first branch cannot be represented in the given precision and results into `rhs`. In the mathematical strict sense, this breaks the definition. But given the limitation of floating point arithmetic it can be thought of the closest representable value to the true result, although it is not strictly in the domain `[0.0, rhs)` of the function. It is rather the left side asymptotical limit. It would be desirable that it produces the mathematical more sound approximation of `0.0`, the right side asymptotical limit. But this breaks the property, that `self == self.div_euc(rhs) * rhs + a.mod_euc(rhs)`.
The discussion in issue #50179 did not find an satisfying conclusion to which property is deemed more important. But at least we can document the behaviour. Which this pull request does.
Add str::split_ascii_whitespace.
As mentioned in #48656.
While `str::split_whitespace` now works in `libcore`, it still makes sense to offer this method, considering how it is still more performant in cases where only ASCII is necessary.
[fuchsia] Update zx_cprng_draw to target semantics
This change is the final step in improving the semantics of
zx_cprng_draw. Now the syscall always generates the requested number of
bytes. If the syscall would have failed to generate the requested number
of bytes, the syscall either terminates the entire operating system or
terminates the calling process, depending on whether the error is a
result of the kernel misbehaving or the userspace program misbehaving.
This change is the final step in improving the semantics of
zx_cprng_draw. Now the syscall always generates the requested number of
bytes. If the syscall would have failed to generate the requested number
of bytes, the syscall either terminates the entire operating system or
terminates the calling process, depending on whether the error is a
result of the kernel misbehaving or the userspace program misbehaving.
Implement `#[macro_export(local_inner_macros)]` (a solution for the macro helper import problem)
Implement a solution for the macro helper issue discussed in https://github.com/rust-lang/rust/issues/35896 as described in https://github.com/rust-lang/rust/issues/35896#issuecomment-395977901.
Macros exported from libraries can be marked with `#[macro_export(local_inner_macros)]` and this annotation changes how nested macros in them are resolved.
If we have a fn-like macro call `ident!(...)` and `ident` comes from a `macro_rules!` macro marked with `#[macro_export(local_inner_macros)]` then it's replaced with `$crate::ident!(...)` and resolved as such (`$crate` gets the same context as `ident`).
This requires us to allocate a single entry vector we didn't use to
allocate. I doubt this makes a difference in practice, as this only
occurs for cache misses.
