Added assert_unsafe_precondition! to check that signed input is nonnegative in debug mode

Author: ChaiTRex

library/core/src/num/int_sqrt.rs

@@ -11,6 +11,8 @@
 //! "Wikipedia contributors. Integer square root. Wikipedia, The Free
 //! Encyclopedia."
 
+use crate::assert_unsafe_precondition;
+
 /// This array stores the [integer square roots][1] and remainders of each
 /// [`u8`](prim@u8) value. For example, `U8_ISQRT_WITH_REMAINDER[17]` will be
 /// `(4, 1)` because the integer square root of 17 is 4 and because 17 is 1
@@ -96,6 +98,16 @@ macro_rules! signed_fn {
                       without modifying the original"]
         #[inline(always)]
         pub const unsafe fn $SignedT(n: $SignedT) -> $SignedT {
+            assert_unsafe_precondition!(
+                check_library_ub,
+                concat!(
+                    "`isqrt` internal error: Passing a negative number to `core::num::int_sqrt::",
+                    stringify!($SignedT),
+                    "` causes undefined behavior."
+                ),
+                (n: $SignedT = n) => n >= 0
+            );
+
             $UnsignedT(n as $UnsignedT) as $SignedT
         }
     };