mandelbrot Dart #2 program

/* The Computer Language Benchmarks Game
   https://salsa.debian.org/benchmarksgame-team/benchmarksgame/

   contributed by Alexander Fyodorov
*/

import 'dart:io';
import 'dart:isolate';
import 'dart:async';
import 'dart:typed_data';

void main(args) {
  int n = args.length > 0 ? int.parse(args[0]) : 2000;

  var threads = Platform.numberOfProcessors;
  var segmentFutures = new List<Future>(threads);

  var segmentSize = new List.filled(threads, n ~/ threads);
  segmentSize[0] += n % threads;

  int from = 0;
  for (int i = 0; i < threads; i++) {
    var len = segmentSize[i];
    var response = new ReceivePort();
    int localFrom = from;
    Future<Isolate> remote = Isolate.spawn(calculateSegment, response.sendPort);
    segmentFutures[i] = remote.then((_) => response.first).then((sendPort) {
      ReceivePort response = new ReceivePort();
      sendPort.send({
        'n': n,
        'from': localFrom,
        'len': len,
        'port': response.sendPort
      });
      return response.first;
    });
    from += len;
  }

  stdout.write('P4\n$n $n\n');

  Future.wait(segmentFutures).then((segments) {
    for (var segment in segments) {
      for (var line in segment) {
        stdout.add(line);
      }
    }
  });
}

Uint8List calculateLine (int n, int y) {
  int lineLen = (n - 1) ~/ 8 + 1;

  var line = new Uint8List(lineLen);

  int xbyte = 0, bits = 1;
  double ci = y * 2.0 / n - 1.0;

  for (int x = 0; x < n; x++) {
    double cr = x * 2.0 / n - 1.5;
    if (bits > 0xff) {
      line[xbyte++] = bits;
      bits = 1;
    }
    double zr = cr,
        zi = ci,
        tr = cr * cr,
        ti = ci * ci;
    int i = 49;
    do {
      zi = zr * zi + zr * zi + ci;
      zr = tr - ti + cr;
      tr = zr * zr;
      ti = zi * zi;
    } while ((tr + ti <= 4.0) && (--i > 0));
    bits = (bits << 1) | (i == 0 ? 1 : 0);
  } while (bits < 0x100) bits = (bits << 1);
  line[xbyte] = bits;

  return line;
}

void calculateSegment (SendPort initialReplyTo) {
  var port = new ReceivePort();
  initialReplyTo.send(port.sendPort);
  port.listen((msg) {
    int n = msg['n'];
    int from = msg['from'];
    int len = msg['len'];
    SendPort replyTo = msg['port'];

    var lines = new List<Uint8List>(len);
    for (int i = 0; i < len; i++) {
      lines[i] = calculateLine(n, from + i);
    }
    replyTo.send(lines);
    port.close();
  });
}
    

NOTES:
64-bit Ubuntu quad core
Dart VM version: 2.8.1 (stable) (Unknown timestamp) on "linux_x64"


Wed, 06 May 2020 19:57:57 GMT

MAKE:
/usr/bin/dartanalyzer mandelbrot.dart-2.dart
make: /usr/bin/dartanalyzer: Command not found
make: [/home/dunham/8000-benchmarksgame/nanobench/makefiles/u64q.programs.Makefile:445: mandelbrot.dart-2.dart_run] Error 127 (ignored)

0.08s to complete and log all make actions

COMMAND LINE:
/usr/bin/dart  mandelbrot.dart-2.dart 16000

(BINARY) PROGRAM OUTPUT NOT SHOWN