Minor improvements

src/main.rs

@@ -230,12 +230,7 @@ const RCAL_VAL: f32 = 1000.0;
 
 /// Convert raw 18-bit 2's complement value to signed i32
 fn sign_extend_18bit(val: u32) -> i32 {
-    let masked = val & 0x3FFFF;
-    if masked & (1 << 17) != 0 {
-        (masked | 0xFFFC0000) as i32
-    } else {
-        masked as i32
-    }
+    ((val << 14) as i32) >> 14
 }
 
 /// Calculate magnitude and phase of Rz using Rcal reference