rework Math.f16round

CHANGELOG.md

@@ -1,6 +1,8 @@
 ## Changelog
 ##### Unreleased
 - Added [`ArrayBuffer.prototype.{ transfer, transferToFixedLength }`](https://github.com/tc39/proposal-arraybuffer-transfer) and support transferring of `ArrayBuffer`s via [`structuredClone`](https://html.spec.whatwg.org/multipage/structured-data.html#dom-structuredclone) to engines with `MessageChannel`
+- Optimized [`Math.f16round`](https://github.com/tc39/proposal-float16array) polyfill
+- Fixed [some conversion cases](https://github.com/petamoriken/float16/issues/1046) of `Math.f16round`
 - Fully forced polyfilling of [the TC39 `Observable` proposal](https://github.com/tc39/proposal-observable) because of incompatibility with [the new WHATWG `Observable` proposal](https://github.com/WICG/observable)
 - Added an extra workaround of errors with exotic environment objects in `Symbol` polyfill, [#1289](https://github.com/zloirock/core-js/issues/1289)
 - Compat data improvements:

packages/core-js/internals/math-f16round.js

@@ -0,0 +1,29 @@
+'use strict';
+var sign = require('../internals/math-sign');
+
+var abs = Math.abs;
+
+var EPSILON = 2.220446049250313e-16; // Number.EPSILON
+var EPSILON16 = 0.0009765625; // 2 ** -10
+var INVERSE_EPSILON = 1 / EPSILON;
+var MAX16 = 65504; // 2 ** 15 - 2 ** 10
+var MIN16 = 6.103515625e-05; // 2 ** -14
+
+var roundTiesToEven = function (n) {
+  return n + INVERSE_EPSILON - INVERSE_EPSILON;
+};
+
+// `Math.f16round` method implementation
+// https://github.com/tc39/proposal-float16array
+module.exports = Math.f16round || function f16round(x) {
+  var n = +x;
+  var $abs = abs(n);
+  var $sign = sign(n);
+  var a, result;
+  if ($abs < MIN16) return $sign * roundTiesToEven($abs / MIN16 / EPSILON16) * MIN16 * EPSILON16;
+  a = (1 + EPSILON16 / EPSILON) * $abs;
+  result = a - (a - $abs);
+  // eslint-disable-next-line no-self-compare -- NaN check
+  if (result > MAX16 || result !== result) return $sign * Infinity;
+  return $sign * result;
+};

packages/core-js/internals/math-fround.js

@@ -2,14 +2,15 @@
 var sign = require('../internals/math-sign');
 
 var abs = Math.abs;
-var pow = Math.pow;
-var EPSILON = pow(2, -52);
-var EPSILON32 = pow(2, -23);
-var MAX32 = pow(2, 127) * (2 - EPSILON32);
-var MIN32 = pow(2, -126);
+
+var EPSILON = 2.220446049250313e-16; // Number.EPSILON
+var EPSILON32 = 1.1920928955078125e-7; // 2 ** -23;
+var INVERSE_EPSILON = 1 / EPSILON;
+var MAX32 = 3.4028234663852886e+38; // 2 ** 128 - 2 ** 104
+var MIN32 = 1.1754943508222875e-38; // 2 ** -126;
 
 var roundTiesToEven = function (n) {
-  return n + 1 / EPSILON - 1 / EPSILON;
+  return n + INVERSE_EPSILON - INVERSE_EPSILON;
 };
 
 // `Math.fround` method implementation

packages/core-js/modules/esnext.math.f16round.js

@@ -1,16 +1,7 @@
 'use strict';
 var $ = require('../internals/export');
-var IEEE754 = require('../internals/ieee754');
-
-var packIEEE754 = IEEE754.pack;
-var unpackIEEE754 = IEEE754.unpack;
-var $isFinite = isFinite;
+var f16round = require('../internals/math-f16round');
 
 // `Math.f16round` method
 // https://github.com/tc39/proposal-float16array
-$({ target: 'Math', stat: true }, {
-  f16round: function f16round(x) {
-    var n = +x;
-    return $isFinite(n) && n !== 0 ? unpackIEEE754(packIEEE754(n, 10, 2), 10) : n;
-  }
-});
+$({ target: 'Math', stat: true }, { f16round: f16round });

tests/unit-global/esnext.math.f16round.js

@@ -36,6 +36,8 @@ QUnit.test('Math.f16round', assert => {
   assert.same(f16round(-2.980232238769531911744490042422139897126953655970282852649688720703125e-8), -minFloat16);
 
   assert.same(f16round(1.337), 1.3369140625);
+  assert.same(f16round(0.499994), 0.5);
+  assert.same(f16round(7.9999999), 8);
 
   const checker = createConversionChecker(1.1);
   assert.same(f16round(checker), 1.099609375, 'object wrapper');

tests/unit-pure/esnext.math.f16round.js

@@ -35,6 +35,8 @@ QUnit.test('Math.f16round', assert => {
   assert.same(f16round(-2.980232238769531911744490042422139897126953655970282852649688720703125e-8), -minFloat16);
 
   assert.same(f16round(1.337), 1.3369140625);
+  assert.same(f16round(0.499994), 0.5);
+  assert.same(f16round(7.9999999), 8);
 
   const checker = createConversionChecker(1.1);
   assert.same(f16round(checker), 1.099609375, 'object wrapper');