Import wpt@503f5b5f78ec4e87d144f78609f363f0ed0ea8db

third_party/WebKit/LayoutTests/external/wpt/streams/readable-streams/floating-point-total-queue-size.js

+'use strict';
+
+if (self.importScripts) {
+  self.importScripts('/resources/testharness.js');
+}
+
+// Due to the limitations of floating-point precision, the calculation of desiredSize sometimes gives different answers
+// than adding up the items in the queue would. It is important that implementations give the same result in these edge
+// cases so that developers do not come to depend on non-standard behaviour. See
+// https://github.com/whatwg/streams/issues/582 and linked issues for further discussion.
+
+promise_test(() => {
+  const { reader, controller } = setupTestStream();
+
+  controller.enqueue(2);
+  assert_equals(controller.desiredSize, 0 - 2, 'desiredSize must be -2 after enqueueing such a chunk');
+
+  controller.enqueue(Number.MAX_SAFE_INTEGER);
+  assert_equals(controller.desiredSize, 0 - Number.MAX_SAFE_INTEGER - 2,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (adding a second chunk)');
+
+  return reader.read().then(() => {
+    assert_equals(controller.desiredSize, 0 - Number.MAX_SAFE_INTEGER - 2 + 2,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a chunk)');
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(controller.desiredSize, 0, '[[queueTotalSize]] must clamp to 0 if it becomes negative');
+  });
+}, 'Floating point arithmetic must manifest near NUMBER.MAX_SAFE_INTEGER (total ends up positive)');
+
+promise_test(() => {
+  const { reader, controller } = setupTestStream();
+
+  controller.enqueue(1e-16);
+  assert_equals(controller.desiredSize, 0 - 1e-16, 'desiredSize must be -1e16 after enqueueing such a chunk');
+
+  controller.enqueue(1);
+  assert_equals(controller.desiredSize, 0 - 1e-16 - 1,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (adding a second chunk)');
+
+  return reader.read().then(() => {
+    assert_equals(controller.desiredSize, 0 - 1e-16 - 1 + 1e-16,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a chunk)');
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(controller.desiredSize, 0, '[[queueTotalSize]] must clamp to 0 if it becomes negative');
+  });
+}, 'Floating point arithmetic must manifest near 0 (total ends up positive, but clamped)');
+
+promise_test(() => {
+  const { reader, controller } = setupTestStream();
+
+  controller.enqueue(1e-16);
+  assert_equals(controller.desiredSize, 0 - 1e-16, 'desiredSize must be -2e16 after enqueueing such a chunk');
+
+  controller.enqueue(1);
+  assert_equals(controller.desiredSize, 0 - 1e-16 - 1,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (adding a second chunk)');
+
+  controller.enqueue(2e-16);
+  assert_equals(controller.desiredSize, 0 - 1e-16 - 1 - 2e-16,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (adding a third chunk)');
+
+  return reader.read().then(() => {
+    assert_equals(controller.desiredSize, 0 - 1e-16 - 1 - 2e-16 + 1e-16,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a chunk)');
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(controller.desiredSize, 0 - 1e-16 - 1 - 2e-16 + 1e-16 + 1,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a second chunk)');
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(controller.desiredSize, 0 - 1e-16 - 1 - 2e-16 + 1e-16 + 1 + 2e-16,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a third chunk)');
+  });
+}, 'Floating point arithmetic must manifest near 0 (total ends up positive, and not clamped)');
+
+promise_test(() => {
+  const { reader, controller } = setupTestStream();
+
+  controller.enqueue(2e-16);
+  assert_equals(controller.desiredSize, 0 - 2e-16, 'desiredSize must be -2e16 after enqueueing such a chunk');
+
+  controller.enqueue(1);
+  assert_equals(controller.desiredSize, 0 - 2e-16 - 1,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (adding a second chunk)');
+
+  return reader.read().then(() => {
+    assert_equals(controller.desiredSize, 0 - 2e-16 - 1 + 2e-16,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a chunk)');
+
+    return reader.read();
+  }).then(() => {
+    assert_equals(controller.desiredSize, 0,
+      'desiredSize must be calculated using double-precision floating-point arithmetic (subtracting a second chunk)');
+  });
+}, 'Floating point arithmetic must manifest near 0 (total ends up zero)');
+
+function setupTestStream() {
+  const strategy = {
+    size(x) {
+      return x;
+    },
+    highWaterMark: 0
+  };
+
+  let controller;
+  const rs = new ReadableStream({
+    start(c) {
+      controller = c;
+    }
+  }, strategy);
+
+  return { reader: rs.getReader(), controller };
+}