add challenge for safety of primitive conversions

doc/src/SUMMARY.md

@@ -26,4 +26,4 @@
   - [11: Safety of Methods for Numeric Primitive Types](./challenges/0011-floats-ints.md)
   - [12: Safety of `NonZero`](./challenges/0012-nonzero.md)
   - [13: Safety of `CStr`](./challenges/0013-cstr.md)
-
+  - [14: Safety of Primitive Conversions](./challenges/0014-convert-num.md)

doc/src/challenges/0014-convert-num.md

@@ -0,0 +1,140 @@
+# Challenge 14: Safety of Primitive Conversions
+
+- **Status:** Open
+- **Tracking Issue:** https://github.com/model-checking/verify-rust-std/issues/220
+- **Start date:** 2024/12/15
+- **End date:** 2025/2/28
+- **Prize:** *TBD*
+
+-------------------
+
+## Goal
+
+Verify the safety of number conversions in `core::convert::num`.
+
+There are three classes of conversions that use unsafe code. All conversions use macros to implement traits for primitive types in bulk. You will need to add contracts into the macros so that contracts are generated for each implementation. As the conversions are all macro generated, it is probably a good idea to write your own macro for generating the harnesses.
+
+### Success Criteria
+
+#### Safety for Float to Int
+
+```rust
+macro_rules! impl_float_to_int {
+    ($Float:ty => $($Int:ty),+) => {
+        #[unstable(feature = "convert_float_to_int", issue = "67057")]
+        impl private::Sealed for $Float {}
+        $(
+            #[unstable(feature = "convert_float_to_int", issue = "67057")]
+            impl FloatToInt<$Int> for $Float {
+                #[inline]
+                unsafe fn to_int_unchecked(self) -> $Int {
+                    // SAFETY: the safety contract must be upheld by the caller.
+                    unsafe { crate::intrinsics::float_to_int_unchecked(self) }
+                }
+            }
+        )+
+    }
+}
+```
+
+The safety constraints referenced in the comments are that the input value must:
+- Not be NaN
+- Not be infinite
+- Be representable in the return type Int, after truncating off its fractional part
+
+These constraints are given in the [documenation](https://doc.rust-lang.org/std/primitive.f32.html#method.to_int_unchecked). 
+
+The intrinsic corresponds to the [fptoui](https://llvm.org/docs/LangRef.html#fptoui-to-instruction)/[fptosi](https://llvm.org/docs/LangRef.html#fptosi-to-instruction) LLVM instructions, which may be useful for reference.
+
+#### NonZero Conversions
+
+Write a type invariant for `core::num::NonZero`, then write harnesses for all `nonzero` conversions.
+
+There are two macros that implement these conversions: an infallible and fallible version. These are all of the types for which conversions are implemented. You should be able to use the macro to generate the function contracts. 
+
+non-zero unsigned integer -> non-zero unsigned integer
+- `impl_nonzero_int_from_nonzero_int!(u8 => u16);`
+- `impl_nonzero_int_from_nonzero_int!(u8 => u32);`
+- `impl_nonzero_int_from_nonzero_int!(u8 => u64);`
+- `impl_nonzero_int_from_nonzero_int!(u8 => u128);`
+- `impl_nonzero_int_from_nonzero_int!(u8 => usize);`
+- `impl_nonzero_int_from_nonzero_int!(u16 => u32);`
+- `impl_nonzero_int_from_nonzero_int!(u16 => u64);`
+- `impl_nonzero_int_from_nonzero_int!(u16 => u128);`
+- `impl_nonzero_int_from_nonzero_int!(u16 => usize);`
+- `impl_nonzero_int_from_nonzero_int!(u32 => u64);`
+- `impl_nonzero_int_from_nonzero_int!(u32 => u128);`
+- `impl_nonzero_int_from_nonzero_int!(u64 => u128);`
+
+non-zero signed integer -> non-zero signed integer
+- `impl_nonzero_int_from_nonzero_int!(i8 => i16);`
+- `impl_nonzero_int_from_nonzero_int!(i8 => i32);`
+- `impl_nonzero_int_from_nonzero_int!(i8 => i64);`
+- `impl_nonzero_int_from_nonzero_int!(i8 => i128);`
+- `impl_nonzero_int_from_nonzero_int!(i8 => isize);`
+- `impl_nonzero_int_from_nonzero_int!(i16 => i32);`
+- `impl_nonzero_int_from_nonzero_int!(i16 => i64);`
+- `impl_nonzero_int_from_nonzero_int!(i16 => i128);`
+- `impl_nonzero_int_from_nonzero_int!(i16 => isize);`
+- `impl_nonzero_int_from_nonzero_int!(i32 => i64);`
+- `impl_nonzero_int_from_nonzero_int!(i32 => i128);`
+- `impl_nonzero_int_from_nonzero_int!(i64 => i128);`
+
+non-zero unsigned -> non-zero signed integer
+- `impl_nonzero_int_from_nonzero_int!(u8 => i16);`
+- `impl_nonzero_int_from_nonzero_int!(u8 => i32);`
+- `impl_nonzero_int_from_nonzero_int!(u8 => i64);`
+- `impl_nonzero_int_from_nonzero_int!(u8 => i128);`
+- `impl_nonzero_int_from_nonzero_int!(u8 => isize);`
+- `impl_nonzero_int_from_nonzero_int!(u16 => i32);`
+- `impl_nonzero_int_from_nonzero_int!(u16 => i64);`
+- `impl_nonzero_int_from_nonzero_int!(u16 => i128);`
+- `impl_nonzero_int_from_nonzero_int!(u32 => i64);`
+- `impl_nonzero_int_from_nonzero_int!(u32 => i128);`
+- `impl_nonzero_int_from_nonzero_int!(u64 => i128);`
+
+There are also the fallible versions.
+
+unsigned non-zero integer -> unsigned non-zero integer
+- `impl_nonzero_int_try_from_nonzero_int!(u16 => u8);`
+- `impl_nonzero_int_try_from_nonzero_int!(u32 => u8, u16, usize);`
+- `impl_nonzero_int_try_from_nonzero_int!(u64 => u8, u16, u32, usize);`
+- `impl_nonzero_int_try_from_nonzero_int!(u128 => u8, u16, u32, u64, usize);`
+- `impl_nonzero_int_try_from_nonzero_int!(usize => u8, u16, u32, u64, u128);`
+
+signed non-zero integer -> signed non-zero integer
+- `impl_nonzero_int_try_from_nonzero_int!(i16 => i8);`
+- `impl_nonzero_int_try_from_nonzero_int!(i32 => i8, i16, isize);`
+- `impl_nonzero_int_try_from_nonzero_int!(i64 => i8, i16, i32, isize);`
+- `impl_nonzero_int_try_from_nonzero_int!(i128 => i8, i16, i32, i64, isize);`
+- `impl_nonzero_int_try_from_nonzero_int!(isize => i8, i16, i32, i64, i128);`
+
+unsigned non-zero integer -> signed non-zero integer
+- `impl_nonzero_int_try_from_nonzero_int!(u8 => i8);`
+- `impl_nonzero_int_try_from_nonzero_int!(u16 => i8, i16, isize);`
+- `impl_nonzero_int_try_from_nonzero_int!(u32 => i8, i16, i32, isize);`
+- `impl_nonzero_int_try_from_nonzero_int!(u64 => i8, i16, i32, i64, isize);`
+- `impl_nonzero_int_try_from_nonzero_int!(u128 => i8, i16, i32, i64, i128, isize);`
+- `impl_nonzero_int_try_from_nonzero_int!(usize => i8, i16, i32, i64, i128, isize);`
+
+signed non-zero integer -> unsigned non-zero integer
+- `impl_nonzero_int_try_from_nonzero_int!(i8 => u8, u16, u32, u64, u128, usize);`
+- `impl_nonzero_int_try_from_nonzero_int!(i16 => u8, u16, u32, u64, u128, usize);`
+- `impl_nonzero_int_try_from_nonzero_int!(i32 => u8, u16, u32, u64, u128, usize);`
+- `impl_nonzero_int_try_from_nonzero_int!(i64 => u8, u16, u32, u64, u128, usize);`
+- `impl_nonzero_int_try_from_nonzero_int!(i128 => u8, u16, u32, u64, u128, usize);`
+- `impl_nonzero_int_try_from_nonzero_int!(isize => u8, u16, u32, u64, u128, usize);`
+
+### List of UBs
+
+In addition to any properties called out as `SAFETY` comments in the source
+code,
+all proofs must automatically ensure the absence of the following [undefined behaviors](https://github.com/rust-lang/reference/blob/142b2ed77d33f37a9973772bd95e6144ed9dce43/src/behavior-considered-undefined.md):
+
+* Accessing (loading from or storing to) a place that is dangling or based on a misaligned pointer.
+* Reading from uninitialized memory.
+* Mutating immutable bytes.
+* Producing an invalid value
+
+Note: All solutions to verification challenges need to satisfy the criteria established in the [challenge book](../general-rules.md)
+in addition to the ones listed above.