A better explanation for change in differentials

src/flamegraph/mod.rs

@@ -616,21 +616,30 @@ where
                     "{} ({} {}, {:.2}%)",
                     function, samples_txt, opt.count_name, pct
                 ),
-                // Special case delta == 0 so we don't format percentage with a + sign.
-                Some(delta) if delta == 0 => write!(
-                    buffer,
-                    "{} ({} {}, {:.2}%; 0.00%)",
-                    function, samples_txt, opt.count_name, pct,
-                ),
-                Some(mut delta) => {
-                    if opt.negate_differentials {
-                        delta = -delta;
-                    }
-                    let delta_pct = (100 * delta) as f64 / (timemax as f64 * opt.factor);
+                Some(delta) => {
+                    let samples = frame.end_time as isize - frame.start_time as isize;
+                    let (old, new) = if opt.negate_differentials {
+                        (samples, samples - delta)
+                    } else {
+                        (samples - delta, samples)
+                    };
+                    let change = match (old, new) {
+                        (0, _) => "all newly added".to_string(),
+                        (_, 0) => "were all removed".to_string(),
+                        (x, y) if x == y => "".to_string(),
+                        (old, new) => {
+                            let (ratio, compared_to) = if opt.negate_differentials {
+                                (old as f64 / new as f64, "new")
+                            } else {
+                                (new as f64 / old as f64, "old")
+                            };
+                            format!(" = {ratio:.3} × {compared_to} {}", opt.count_name)
+                        }
+                    };
                     write!(
                         buffer,
-                        "{} ({} {}, {:.2}%; {:+.2}%)",
-                        function, samples_txt, opt.count_name, pct, delta_pct
+                        "{} ({} {} {}, {:.2}%)",
+                        function, samples_txt, opt.count_name, change, pct
                     )
                 }
             }