Tweak low-level benchmark.

Author: lrhn

pkgs/characters/tool/benchmark.dart

@@ -10,16 +10,16 @@ import '../test/src/unicode_grapheme_tests.dart';
 import '../test/src/various_tests.dart';
 
 // Low-level benchmark of the grapheme cluster step functions.
+// Use ../benchmark/benchmark.dart for the more high-level `Characters`
+// methods.
 
 void main(List<String> args) {
   var count = 5;
   if (args.isNotEmpty) {
     count = int.parse(args[0]);
   }
-  var gcSumForward = 0;
-  var gcSumBackwards = 0;
-
-  var text = genesis +
+  var text =
+      genesis +
       hangul +
       genesis +
       diacretics +
@@ -28,9 +28,20 @@ void main(List<String> args) {
       recJoin(zalgo);
   var codeUnits = text.length;
   var codePoints = text.runes.length;
+  // Warmup.
+  var gcSumForward = benchForward(text, -1, codePoints, codeUnits, 150);
+  var gcSumBackwards = benchBackward(text, -1, codePoints, codeUnits, 150);
+  if (gcSumForward != gcSumBackwards) {
+    print(
+      'ERROR: Did not count the same number of grapheme clusters: '
+      '$gcSumForward forward vs. $gcSumBackwards backward.',
+    );
+    return;
+  }
+
   for (var i = 0; i < count; i++) {
-    gcSumForward = benchForward(text, i, codePoints, codeUnits);
-    gcSumBackwards = benchBackward(text, i, codePoints, codeUnits);
+    gcSumForward = benchForward(text, i, codePoints, codeUnits, 1500);
+    gcSumBackwards = benchBackward(text, i, codePoints, codeUnits, 1500);
   }
   print('gc: Grapheme Clusters, cp: Code Points, cu: Code Units.');
   if (gcSumForward != gcSumBackwards) {
@@ -39,7 +50,12 @@ void main(List<String> args) {
       '$gcSumForward forward vs. $gcSumBackwards backward.',
     );
   } else {
-    print('Total: $gcSumForward gc, $codePoints cp, $codeUnits cu');
+    var surrogates = codeUnits - codePoints;
+    print(
+      'Total: $gcSumForward gc, $codePoints cp, $codeUnits cu, '
+      '$surrogates surrogates '
+      '(${(surrogates / codePoints * 100).toStringAsFixed(3)}%)',
+    );
     print('Avg ${(codePoints / gcSumForward).toStringAsFixed(3)} cp/gc');
     print('Avg ${(codeUnits / gcSumForward).toStringAsFixed(3)} cu/gc');
   }
@@ -48,46 +64,58 @@ void main(List<String> args) {
 String recJoin(Iterable<List<String>> texts) =>
     texts.map((x) => x.join('')).join('\n');
 
-int benchForward(String text, int i, int cp, int cu) {
+int benchForward(String text, int round, int cp, int cu, int limit) {
   var n = 0;
+  var step = 10;
   var gc = 0;
   var e = 0;
   var sw = Stopwatch()..start();
   do {
-    var breaks = Breaks(text, 0, text.length, stateSoTNoBreak);
-    while (breaks.nextBreak() >= 0) {
-      gc++;
+    for (var i = 0; i < step; i++) {
+      var breaks = Breaks(text, 0, text.length, stateSoTNoBreak);
+      while (breaks.nextBreak() >= 0) {
+        gc++;
+      }
     }
     e = sw.elapsedMilliseconds;
-    n++;
-  } while (e < 2000);
-  print(
-    'Forward  #$i: ${(gc / e).round()} gc/ms, '
-    '${(n * cp / e).round()} cp/ms, '
-    '${(n * cu / e).round()} cu/ms, '
-    '$n rounds',
-  );
+    n += step;
+    step += step;
+  } while (e < limit);
+  if (limit > 500) {
+    print(
+      'Forward  #$round: ${(gc / e).round()} gc/ms, '
+      '${(n * cp / e).round()} cp/ms, '
+      '${(n * cu / e).round()} cu/ms, '
+      '$n rounds in $e ms',
+    );
+  }
   return gc ~/ n;
 }
 
-int benchBackward(String text, int i, int cp, int cu) {
+int benchBackward(String text, int round, int cp, int cu, int limit) {
   var n = 0;
+  var step = 10;
   var gc = 0;
   var e = 0;
   var sw = Stopwatch()..start();
   do {
-    var breaks = BackBreaks(text, text.length, 0, stateEoTNoBreak);
-    while (breaks.nextBreak() >= 0) {
-      gc++;
+    for (var i = 0; i < step; i++) {
+      var breaks = BackBreaks(text, text.length, 0, stateEoTNoBreak);
+      while (breaks.nextBreak() >= 0) {
+        gc++;
+      }
     }
     e = sw.elapsedMilliseconds;
-    n++;
-  } while (e < 2000);
-  print(
-    'Backward #$i: ${(gc / e).round()} gc/ms, '
-    '${(n * cp / e).round()} cp/ms, '
-    '${(n * cu / e).round()} cu/ms, '
-    '$n rounds',
-  );
+    n += step;
+    step += step;
+  } while (e < limit);
+  if (limit > 500) {
+    print(
+      'Backward #$round: ${(gc / e).round()} gc/ms, '
+      '${(n * cp / e).round()} cp/ms, '
+      '${(n * cu / e).round()} cu/ms, '
+      '$n rounds in $e ms',
+    );
+  }
   return gc ~/ n;
 }