Add Float::max_int_bits

Returns the number of bits needed to represent the largest integer that a floating point type can hold.

Bumps LLVM commit to 038f7debfda01471ce0d4eb1fed20da61e5c8b32, where this was added upstream.

Author: eduardosm

Cargo.toml

@@ -2,7 +2,7 @@
 members = ["fuzz"]
 
 [workspace.package]
-version = "0.2.0+llvm-4dc08de9d2f6"
+version = "0.2.0+llvm-038f7debfda0"
 edition = "2021"
 license = "Apache-2.0 WITH LLVM-exception"
 

src/lib.rs

@@ -1,6 +1,6 @@
 //! Port of LLVM's APFloat software floating-point implementation from the
 //! following C++ sources (please update commit hash when backporting):
-//! https://github.com/llvm/llvm-project/commit/4dc08de9d2f680309cdd639169d3b8802c76ae9a
+//! https://github.com/llvm/llvm-project/commit/038f7debfda01471ce0d4eb1fed20da61e5c8b32
 //! * `llvm/include/llvm/ADT/APFloat.h` -> `Float` and `FloatConvert` traits
 //! * `llvm/lib/Support/APFloat.cpp` -> `ieee` and `ppc` modules
 //! * `llvm/unittests/ADT/APFloatTest.cpp` -> `tests` directory
@@ -263,6 +263,16 @@ pub trait Float:
     // FIXME(eddyb) provide a default when qnan becomes const fn.
     const NAN: Self;
 
+    /// Number of bits needed to represent the largest integer that
+    /// the floating point type can hold.
+    // FIXME should be const fn.
+    fn max_int_bits(signed: bool) -> usize {
+        // The max FP value is pow(2, MaxExponent) * (1 + MaxFraction), so we need
+        // at least one more bit than the MaxExponent to hold the max FP value.
+        // Another extra sign bit is needed for signed integers.
+        Self::MAX_EXP as usize + 1 + (signed as usize)
+    }
+
     /// Factory for QNaN values.
     // FIXME(eddyb) should be const fn.
     fn qnan(payload: Option<u128>) -> Self;