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							151 lines
						
					
					
						
							4.6 KiB
						
					
					
				| 'use strict'; | |
| // based on Shewchuk's algorithm for exactly floating point addition | |
| // adapted from https://github.com/tc39/proposal-math-sum/blob/3513d58323a1ae25560e8700aa5294500c6c9287/polyfill/polyfill.mjs | |
| var $ = require('../internals/export'); | |
| var uncurryThis = require('../internals/function-uncurry-this'); | |
| var iterate = require('../internals/iterate'); | |
| 
 | |
| var $RangeError = RangeError; | |
| var $TypeError = TypeError; | |
| var $Infinity = Infinity; | |
| var $NaN = NaN; | |
| var abs = Math.abs; | |
| var pow = Math.pow; | |
| var push = uncurryThis([].push); | |
| 
 | |
| var POW_2_1023 = pow(2, 1023); | |
| var MAX_SAFE_INTEGER = pow(2, 53) - 1; // 2 ** 53 - 1 === 9007199254740992 | |
| var MAX_DOUBLE = Number.MAX_VALUE; // 2 ** 1024 - 2 ** (1023 - 52) === 1.79769313486231570815e+308 | |
| var MAX_ULP = pow(2, 971); // 2 ** (1023 - 52) === 1.99584030953471981166e+292 | |
|  | |
| var NOT_A_NUMBER = {}; | |
| var MINUS_INFINITY = {}; | |
| var PLUS_INFINITY = {}; | |
| var MINUS_ZERO = {}; | |
| var FINITE = {}; | |
| 
 | |
| // prerequisite: abs(x) >= abs(y) | |
| var twosum = function (x, y) { | |
|   var hi = x + y; | |
|   var lo = y - (hi - x); | |
|   return { hi: hi, lo: lo }; | |
| }; | |
| 
 | |
| // `Math.sumPrecise` method | |
| // https://github.com/tc39/proposal-math-sum | |
| $({ target: 'Math', stat: true, forced: true }, { | |
|   // eslint-disable-next-line max-statements -- ok | |
|   sumPrecise: function sumPrecise(items) { | |
|     var numbers = []; | |
|     var count = 0; | |
|     var state = MINUS_ZERO; | |
| 
 | |
|     iterate(items, function (n) { | |
|       if (++count >= MAX_SAFE_INTEGER) throw new $RangeError('Maximum allowed index exceeded'); | |
|       if (typeof n != 'number') throw new $TypeError('Value is not a number'); | |
|       if (state !== NOT_A_NUMBER) { | |
|         // eslint-disable-next-line no-self-compare -- NaN check | |
|         if (n !== n) state = NOT_A_NUMBER; | |
|         else if (n === $Infinity) state = state === MINUS_INFINITY ? NOT_A_NUMBER : PLUS_INFINITY; | |
|         else if (n === -$Infinity) state = state === PLUS_INFINITY ? NOT_A_NUMBER : MINUS_INFINITY; | |
|         else if ((n !== 0 || (1 / n) === $Infinity) && (state === MINUS_ZERO || state === FINITE)) { | |
|           state = FINITE; | |
|           push(numbers, n); | |
|         } | |
|       } | |
|     }); | |
| 
 | |
|     switch (state) { | |
|       case NOT_A_NUMBER: return $NaN; | |
|       case MINUS_INFINITY: return -$Infinity; | |
|       case PLUS_INFINITY: return $Infinity; | |
|       case MINUS_ZERO: return -0; | |
|     } | |
| 
 | |
|     var partials = []; | |
|     var overflow = 0; // conceptually 2 ** 1024 times this value; the final partial is biased by this amount | |
|     var x, y, sum, hi, lo, tmp; | |
| 
 | |
|     for (var i = 0; i < numbers.length; i++) { | |
|       x = numbers[i]; | |
|       var actuallyUsedPartials = 0; | |
|       for (var j = 0; j < partials.length; j++) { | |
|         y = partials[j]; | |
|         if (abs(x) < abs(y)) { | |
|           tmp = x; | |
|           x = y; | |
|           y = tmp; | |
|         } | |
|         sum = twosum(x, y); | |
|         hi = sum.hi; | |
|         lo = sum.lo; | |
|         if (abs(hi) === $Infinity) { | |
|           var sign = hi === $Infinity ? 1 : -1; | |
|           overflow += sign; | |
| 
 | |
|           x = (x - (sign * POW_2_1023)) - (sign * POW_2_1023); | |
|           if (abs(x) < abs(y)) { | |
|             tmp = x; | |
|             x = y; | |
|             y = tmp; | |
|           } | |
|           sum = twosum(x, y); | |
|           hi = sum.hi; | |
|           lo = sum.lo; | |
|         } | |
|         if (lo !== 0) partials[actuallyUsedPartials++] = lo; | |
|         x = hi; | |
|       } | |
|       partials.length = actuallyUsedPartials; | |
|       if (x !== 0) push(partials, x); | |
|     } | |
| 
 | |
|     // compute the exact sum of partials, stopping once we lose precision | |
|     var n = partials.length - 1; | |
|     hi = 0; | |
|     lo = 0; | |
| 
 | |
|     if (overflow !== 0) { | |
|       var next = n >= 0 ? partials[n] : 0; | |
|       n--; | |
|       if (abs(overflow) > 1 || (overflow > 0 && next > 0) || (overflow < 0 && next < 0)) { | |
|         return overflow > 0 ? $Infinity : -$Infinity; | |
|       } | |
|       // here we actually have to do the arithmetic | |
|       // drop a factor of 2 so we can do it without overflow | |
|       // assert(abs(overflow) === 1) | |
|       sum = twosum(overflow * POW_2_1023, next / 2); | |
|       hi = sum.hi; | |
|       lo = sum.lo; | |
|       lo *= 2; | |
|       if (abs(2 * hi) === $Infinity) { | |
|         // rounding to the maximum value | |
|         if (hi > 0) { | |
|           return (hi === POW_2_1023 && lo === -(MAX_ULP / 2) && n >= 0 && partials[n] < 0) ? MAX_DOUBLE : $Infinity; | |
|         } return (hi === -POW_2_1023 && lo === (MAX_ULP / 2) && n >= 0 && partials[n] > 0) ? -MAX_DOUBLE : -$Infinity; | |
|       } | |
| 
 | |
|       if (lo !== 0) { | |
|         partials[++n] = lo; | |
|         lo = 0; | |
|       } | |
| 
 | |
|       hi *= 2; | |
|     } | |
| 
 | |
|     while (n >= 0) { | |
|       sum = twosum(hi, partials[n--]); | |
|       hi = sum.hi; | |
|       lo = sum.lo; | |
|       if (lo !== 0) break; | |
|     } | |
| 
 | |
|     if (n >= 0 && ((lo < 0 && partials[n] < 0) || (lo > 0 && partials[n] > 0))) { | |
|       y = lo * 2; | |
|       x = hi + y; | |
|       if (y === x - hi) hi = x; | |
|     } | |
| 
 | |
|     return hi; | |
|   } | |
| });
 |