core: add signal name lookup by value

src/uucore/src/lib/features/signals.rs

@@ -349,6 +349,13 @@ pub fn signal_by_name_or_value(signal_name_or_value: &str) -> Option<usize> {
         .map(|s| s.value)
 }
 
+pub fn signal_name_by_value(signal_value: usize) -> Option<&'static str> {
+    ALL_SIGNALS
+        .iter()
+        .find(|signal| signal.value == signal_value)
+        .map(|signal| signal.name)
+}
+
 #[inline(always)]
 pub fn is_signal(num: usize) -> bool {
     // Named signals start at 1
@@ -358,7 +365,7 @@ pub fn is_signal(num: usize) -> bool {
 #[test]
 fn signals_all_contiguous() {
     for (i, signal) in ALL_SIGNALS.iter().enumerate() {
-        assert_eq!(signal.value, i + 1);
+        assert_eq!(signal.value, i);
     }
 }
 
@@ -396,3 +403,10 @@ fn signal_by_long_name() {
         );
     }
 }
+
+#[test]
+fn name() {
+    for signal in &ALL_SIGNALS {
+        assert_eq!(signal_name_by_value(signal.value), Some(signal.name));
+    }
+}