Add 1.45.0 cast documentation

Author: sakex

src/types/cast.md

@@ -59,5 +59,25 @@ fn main() {
     println!("1000 as a u8 is : {}", 1000 as u8);
     // and the two's complement of 232 is -24
     println!(" 232 as a i8 is : {}", 232 as i8);
+    
+    // Since Rust 1.45, the `as` keyword performs a *saturating cast* when casting from float to int.  
+    // If the floating point value exceeds the upper bound or is less than the lower bound, the returned value will be equal to the bound crossed.
+    
+    // 300.0 is 255
+    println!("300.0 is {}", 300.0_f32 as u8);
+    // -100.0 as u8 is 0
+    println!("-100.0 as u8 is {}", -100.0_f32 as u8);
+    // nan as u8 is 0
+    println!("nan as u8 is {}", f32::NAN as u8);
+    
+    // This behavior incures a small runtime cost and can be avoided with unsafe methods:
+    unsafe {
+        // 300.0 is 44
+        println!("300.0 is {}", 300.0_f32.to_int_unchecked::<u8>());
+        // -100.0 as u8 is 156
+        println!("-100.0 as u8 is {}", (-100.0_f32).to_int_unchecked::<u8>());
+        // nan as u8 is 0
+        println!("nan as u8 is {}", f32::NAN.to_int_unchecked::<u8>());
+    }
 }
 ```