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// Copyright (C) 2011 by Ben Noordhuis <info@bnoordhuis.nl>
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
exports.encode = encode;
exports.decode = decode;
var TMIN = 1;
var TMAX = 26;
var BASE = 36;
var SKEW = 38;
var DAMP = 700; // initial bias scaler
var INITIAL_N = 128;
var INITIAL_BIAS = 72;
var MAX_INTEGER = Math.pow(2, 53);
function adapt_bias(delta, n_points, is_first) {
// scale back, then increase delta
delta /= is_first ? DAMP : 2;
delta += ~~(delta / n_points);
var s = (BASE - TMIN);
var t = ~~((s * TMAX) / 2); // threshold=455
for (var k = 0; delta > t; k += BASE) {
delta = ~~(delta / s);
}
var a = (BASE - TMIN + 1) * delta;
var b = (delta + SKEW);
return k + ~~(a / b);
}
function next_smallest_codepoint(codepoints, n) {
var m = 0x110000; // unicode upper bound + 1
for (var i = 0, len = codepoints.length; i < len; ++i) {
var c = codepoints[i];
if (c >= n && c < m) {
m = c;
}
}
// sanity check - should not happen
if (m >= 0x110000) {
throw new Error('Next smallest code point not found.');
}
return m;
}
function encode_digit(d) {
return d + (d < 26 ? 97 : 22);
}
function decode_digit(d) {
if (d >= 48 && d <= 57) {
return d - 22; // 0..9
}
if (d >= 65 && d <= 90) {
return d - 65; // A..Z
}
if (d >= 97 && d <= 122) {
return d - 97; // a..z
}
throw new Error('Illegal digit #' + d);
}
function threshold(k, bias) {
if (k <= bias + TMIN) {
return TMIN;
}
if (k >= bias + TMAX) {
return TMAX;
}
return k - bias;
}
function encode_int(bias, delta) {
var result = [];
for (var k = BASE, q = delta;; k += BASE) {
var t = threshold(k, bias);
if (q < t) {
result.push(encode_digit(q));
break;
}
else {
result.push(encode_digit(t + ((q - t) % (BASE - t))));
q = ~~((q - t) / (BASE - t));
}
}
return result;
}
function encode(input) {
if (typeof input != 'string') {
throw new Error('Argument must be a string.');
}
input = input.split('').map(function(c) {
return c.charCodeAt(0);
});
var output = [];
var non_basic = [];
for (var i = 0, len = input.length; i < len; ++i) {
var c = input[i];
if (c < 128) {
output.push(c);
}
else {
non_basic.push(c);
}
}
var b, h;
b = h = output.length;
if (b) {
output.push(45); // delimiter '-'
}
var n = INITIAL_N;
var bias = INITIAL_BIAS;
var delta = 0;
for (var len = input.length; h < len; ++n, ++delta) {
var m = next_smallest_codepoint(non_basic, n);
delta += (m - n) * (h + 1);
n = m;
for (var i = 0; i < len; ++i) {
var c = input[i];
if (c < n) {
if (++delta == MAX_INTEGER) {
throw new Error('Delta overflow.');
}
}
else if (c == n) {
// TODO append in-place?
// i.e. -> output.push.apply(output, encode_int(bias, delta));
output = output.concat(encode_int(bias, delta));
bias = adapt_bias(delta, h + 1, b == h);
delta = 0;
h++;
}
}
}
return String.fromCharCode.apply(String, output);
}
function decode(input) {
if (typeof input != 'string') {
throw new Error('Argument must be a string.');
}
// find basic code points/delta separator
var b = 1 + input.lastIndexOf('-');
input = input.split('').map(function(c) {
return c.charCodeAt(0);
});
// start with a copy of the basic code points
var output = input.slice(0, b ? (b - 1) : 0);
var n = INITIAL_N;
var bias = INITIAL_BIAS;
for (var i = 0, len = input.length; b < len; ++i) {
var org_i = i;
for (var k = BASE, w = 1;; k += BASE) {
var d = decode_digit(input[b++]);
// TODO overflow check
i += d * w;
var t = threshold(k, bias);
if (d < t) {
break;
}
// TODO overflow check
w *= BASE - t;
}
var x = 1 + output.length;
bias = adapt_bias(i - org_i, x, org_i == 0);
// TODO overflow check
n += ~~(i / x);
i %= x;
output.splice(i, 0, n);
}
return String.fromCharCode.apply(String, output);
}
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