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(function (root, factory) {
"use strict";
// AMD
if (typeof define === 'function' && define.amd) {
define([], factory);
}
// CommonJS
else if (typeof exports === 'object') {
module.exports = factory();
}
// Browser
else {
root.add = factory();
}
})(this, function () {
"use strict";
// The minimum machine rounding error
var Epsilon = Math.pow(2, -53)
, EpsilonReciprocal = (1 / Epsilon)
/// The smallest positive number that can be represented
, Eta = Math.pow(2, -1074)
// limitB is a constant used in the transform function
, limitB = 0.5 * EpsilonReciprocal * Eta
/**
* S. M. RUMP, T. OGITA AND S. OISHI
* http://www.ti3.tu-harburg.de/paper/rump/RuOgOi07I.pdf
*/
// Page 8
// x is result, y is error
// third is so the array is allocated for 4 spaces
// it speeds up transform
function fastTwoSum(a, b) {
var x = a + b
, q = x - a
, y = b - q
return [x, y, null]
}
// Page 12
// p = q + p'
// sigma is a power of 2 greater than or equal to |p|
function extractScalar(sigma, p) {
var q = (sigma + p) - sigma
, pPrime = p - q
return [q, pPrime]
}
// Page 12
function extractVector(sigma, p) {
var tau = 0.0
, extracted
, i = 0
, ii = p.length
, pPrime = new Array(ii)
for(; i<ii; ++i) {
extracted = extractScalar(sigma, p[i])
pPrime[i] = extracted[1]
tau += extracted[0]
}
return [tau, pPrime]
}
// Finds the immediate power of 2 that is larger than p
//// in a fast way
function nextPowerTwo (p) {
var q = EpsilonReciprocal * p
, L = Math.abs((q + p) - q)
if(L === 0)
return Math.abs(p)
return L
}
// Helper, gets the maximum of the absolute values of an array
function maxAbs(arr) {
var i = 0
, ii = arr.length
, best = -1
for(; i<ii; ++i) {
if(Math.abs(arr[i]) > best) {
best = arr[i]
}
}
return best
}
function transform (p) {
var mu = maxAbs(p)
, M
, sigmaPrime
, tPrime
, t
, tau
, sigma
, extracted
, res
// Not part of the original paper, here for optimization
, temp
, bigPow
, limitA
, twoToTheM
if(mu === 0) {
return [0, 0, p, 0]
}
M = nextPowerTwo(p.length + 2)
twoToTheM = Math.pow(2, M)
bigPow = 2 * twoToTheM // equiv to Math.pow(2, 2 * M), faster
sigmaPrime = twoToTheM * nextPowerTwo(mu)
tPrime = 0
do {
t = tPrime
sigma = sigmaPrime
extracted = extractVector(sigma, p)
tau = extracted[0]
tPrime = t + tau
p = extracted[1]
if(tPrime === 0) {
return transform(p)
}
temp = Epsilon * sigma
sigmaPrime = twoToTheM * temp
limitA = bigPow * temp
}
while( Math.abs(tPrime) < limitA && sigma > limitB )
// res already allocated for 4
res = fastTwoSum(t, tau)
res[2] = p
return res
}
function dumbSum(p) {
var i, ii, sum = 0.0
for(i=0, ii=p.length; i<ii; ++i) {
sum += p[i]
}
return sum
}
function accSum(p) {
// Zero length array, or all values are zeros
if(p.length === 0 || maxAbs(p) === 0) {
return 0
}
var tfmd = transform(p)
return tfmd[0] + (tfmd[1] +dumbSum(tfmd[2]))
}
// exports
accSum.dumbSum = dumbSum;
accSum.fastTwoSum = fastTwoSum;
accSum.nextPowerTwo = nextPowerTwo;
return accSum;
});