Implement rounding for the hex float parsing and prepare to improve error handling

Parsing errors are now bubbled up part of the way, but that needs some
more work.

Rounding should be correct, and the `Status` returned by `parse_any`
should have the correct bits set. These are used for the current (unchanged)
behavior of the surface level functions like `hf64`: panic on invalid inputs, or
values that aren't exactly representable.

Author: quaternic

libm/crates/libm-test/src/f8_impl.rs

@@ -3,8 +3,6 @@
 use std::cmp::{self, Ordering};
 use std::{fmt, ops};
 
-use libm::support::hex_float::parse_any;
-
 use crate::Float;
 
 /// Sometimes verifying float logic is easiest when all values can quickly be checked exhaustively
@@ -499,5 +497,6 @@ impl fmt::LowerHex for f8 {
 }
 
 pub const fn hf8(s: &str) -> f8 {
-    f8(parse_any(s, 8, 3) as u8)
+    let Ok(bits) = libm::support::hex_float::parse_hex_exact(s, 8, 3) else { panic!() };
+    f8(bits as u8)
 }

libm/src/math/support/env.rs

@@ -46,7 +46,7 @@ pub enum Round {
 }
 
 /// IEEE 754 exception status flags.
-#[derive(Clone, Copy, Debug, PartialEq)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub struct Status(u8);
 
 impl Status {
@@ -90,16 +90,22 @@ impl Status {
 
     /// True if `UNDERFLOW` is set.
     #[cfg_attr(not(feature = "unstable-public-internals"), allow(dead_code))]
-    pub fn underflow(self) -> bool {
+    pub const fn underflow(self) -> bool {
         self.0 & Self::UNDERFLOW.0 != 0
     }
 
+    /// True if `OVERFLOW` is set.
+    #[cfg_attr(not(feature = "unstable-public-internals"), allow(dead_code))]
+    pub const fn overflow(self) -> bool {
+        self.0 & Self::OVERFLOW.0 != 0
+    }
+
     pub fn set_underflow(&mut self, val: bool) {
         self.set_flag(val, Self::UNDERFLOW);
     }
 
     /// True if `INEXACT` is set.
-    pub fn inexact(self) -> bool {
+    pub const fn inexact(self) -> bool {
         self.0 & Self::INEXACT.0 != 0
     }
 
@@ -114,4 +120,8 @@ impl Status {
             self.0 &= !mask.0;
         }
     }
+
+    pub(crate) const fn with(self, rhs: Self) -> Self {
+        Self(self.0 | rhs.0)
+    }
 }