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Fix IEEE754 rounding rule from truncation to roundTiesToEven #1279

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merged 3 commits into from Aug 6, 2023
Merged

Fix IEEE754 rounding rule from truncation to roundTiesToEven #1279

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2689366
Fix `Math.f16round` unit test
petamoriken Aug 2, 2023
52fe148
Fix IEEE754 rounding rule from truncation to roundTiesToEven
petamoriken Aug 2, 2023
9eb7f3a
Fix for lint
petamoriken Aug 2, 2023
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29 changes: 20 additions & 9 deletions packages/core-js/internals/ieee754.js
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@@ -1,19 +1,30 @@
'use strict';
// IEEE754 conversions based on https://github.com/feross/ieee754
var sign = require('../internals/math-sign');
var trunc = require('../internals/math-trunc');

var $Array = Array;
var abs = Math.abs;
var pow = Math.pow;
var floor = Math.floor;
var log = Math.log;
var LN2 = Math.LN2;

var roundToEven = function (number) {
var truncated = trunc(number);
var delta = abs(number - truncated);
if (delta > 0.5 || delta === 0.5 && truncated % 2 !== 0) {
return truncated + sign(number);
} return truncated;
};

var pack = function (number, mantissaLength, bytes) {
var buffer = $Array(bytes);
var exponentLength = bytes * 8 - mantissaLength - 1;
var eMax = (1 << exponentLength) - 1;
var eBias = eMax >> 1;
var rt = mantissaLength === 23 ? pow(2, -24) - pow(2, -77) : 0;
var sign = number < 0 || number === 0 && 1 / number < 0 ? 1 : 0;
var s = number < 0 || number === 0 && 1 / number < 0 ? 1 : 0;
var index = 0;
var exponent, mantissa, c;
number = abs(number);
Expand Down Expand Up @@ -42,10 +53,10 @@ var pack = function (number, mantissaLength, bytes) {
mantissa = 0;
exponent = eMax;
} else if (exponent + eBias >= 1) {
mantissa = (number * c - 1) * pow(2, mantissaLength);
mantissa = roundToEven((number * c - 1) * pow(2, mantissaLength));
exponent = exponent + eBias;
} else {
mantissa = number * pow(2, eBias - 1) * pow(2, mantissaLength);
mantissa = roundToEven(number * pow(2, eBias - 1) * pow(2, mantissaLength));
exponent = 0;
}
}
Expand All @@ -61,7 +72,7 @@ var pack = function (number, mantissaLength, bytes) {
exponent /= 256;
exponentLength -= 8;
}
buffer[--index] |= sign * 128;
buffer[--index] |= s * 128;
return buffer;
};

Expand All @@ -72,10 +83,10 @@ var unpack = function (buffer, mantissaLength) {
var eBias = eMax >> 1;
var nBits = exponentLength - 7;
var index = bytes - 1;
var sign = buffer[index--];
var exponent = sign & 127;
var s = buffer[index--];
var exponent = s & 127;
var mantissa;
sign >>= 7;
s >>= 7;
while (nBits > 0) {
exponent = exponent * 256 + buffer[index--];
nBits -= 8;
Expand All @@ -90,11 +101,11 @@ var unpack = function (buffer, mantissaLength) {
if (exponent === 0) {
exponent = 1 - eBias;
} else if (exponent === eMax) {
return mantissa ? NaN : sign ? -Infinity : Infinity;
return mantissa ? NaN : s ? -Infinity : Infinity;
} else {
mantissa = mantissa + pow(2, mantissaLength);
exponent = exponent - eBias;
} return (sign ? -1 : 1) * mantissa * pow(2, exponent - mantissaLength);
} return (s ? -1 : 1) * mantissa * pow(2, exponent - mantissaLength);
};

module.exports = {
Expand Down
4 changes: 2 additions & 2 deletions tests/unit-global/esnext.math.f16round.js
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Expand Up @@ -32,8 +32,8 @@ QUnit.test('Math.f16round', assert => {
assert.same(f16round(-minFloat16), -minFloat16);
assert.same(f16round(minFloat16 / 2), 0);
assert.same(f16round(-minFloat16 / 2), -0);
assert.same(f16round(minFloat16 / 2 + 2 ** -25), minFloat16);
assert.same(f16round(-minFloat16 / 2 - 2 ** -25), -minFloat16);
assert.same(f16round(2.980232238769531911744490042422139897126953655970282852649688720703125e-8), minFloat16);
assert.same(f16round(-2.980232238769531911744490042422139897126953655970282852649688720703125e-8), -minFloat16);

assert.same(f16round(1.337), 1.3369140625);

Expand Down
4 changes: 2 additions & 2 deletions tests/unit-pure/esnext.math.f16round.js
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Expand Up @@ -31,8 +31,8 @@ QUnit.test('Math.f16round', assert => {
assert.same(f16round(-minFloat16), -minFloat16);
assert.same(f16round(minFloat16 / 2), 0);
assert.same(f16round(-minFloat16 / 2), -0);
assert.same(f16round(minFloat16 / 2 + 2 ** -25), minFloat16);
assert.same(f16round(-minFloat16 / 2 - 2 ** -25), -minFloat16);
assert.same(f16round(2.980232238769531911744490042422139897126953655970282852649688720703125e-8), minFloat16);
assert.same(f16round(-2.980232238769531911744490042422139897126953655970282852649688720703125e-8), -minFloat16);

assert.same(f16round(1.337), 1.3369140625);

Expand Down