'use strict'
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var ALPHABET = 'qpzry9x8gf2tvdw0s3jn54khce6mua7l'
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// pre-compute lookup table
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var ALPHABET_MAP = {}
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for (var z = 0; z < ALPHABET.length; z++) {
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var x = ALPHABET.charAt(z)
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if (ALPHABET_MAP[x] !== undefined) throw new TypeError(x + ' is ambiguous')
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ALPHABET_MAP[x] = z
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}
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function polymodStep (pre) {
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var b = pre >> 25
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return ((pre & 0x1FFFFFF) << 5) ^
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(-((b >> 0) & 1) & 0x3b6a57b2) ^
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(-((b >> 1) & 1) & 0x26508e6d) ^
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(-((b >> 2) & 1) & 0x1ea119fa) ^
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(-((b >> 3) & 1) & 0x3d4233dd) ^
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(-((b >> 4) & 1) & 0x2a1462b3)
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}
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function prefixChk (prefix) {
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var chk = 1
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for (var i = 0; i < prefix.length; ++i) {
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var c = prefix.charCodeAt(i)
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if (c < 33 || c > 126) return 'Invalid prefix (' + prefix + ')'
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chk = polymodStep(chk) ^ (c >> 5)
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}
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chk = polymodStep(chk)
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for (i = 0; i < prefix.length; ++i) {
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var v = prefix.charCodeAt(i)
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chk = polymodStep(chk) ^ (v & 0x1f)
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}
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return chk
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}
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function encode (prefix, words, LIMIT) {
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LIMIT = LIMIT || 90
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if ((prefix.length + 7 + words.length) > LIMIT) throw new TypeError('Exceeds length limit')
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prefix = prefix.toLowerCase()
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// determine chk mod
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var chk = prefixChk(prefix)
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if (typeof chk === 'string') throw new Error(chk)
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var result = prefix + '1'
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for (var i = 0; i < words.length; ++i) {
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var x = words[i]
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if ((x >> 5) !== 0) throw new Error('Non 5-bit word')
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chk = polymodStep(chk) ^ x
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result += ALPHABET.charAt(x)
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}
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for (i = 0; i < 6; ++i) {
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chk = polymodStep(chk)
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}
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chk ^= 1
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for (i = 0; i < 6; ++i) {
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var v = (chk >> ((5 - i) * 5)) & 0x1f
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result += ALPHABET.charAt(v)
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}
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return result
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}
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function __decode (str, LIMIT) {
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LIMIT = LIMIT || 90
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if (str.length < 8) return str + ' too short'
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if (str.length > LIMIT) return 'Exceeds length limit'
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// don't allow mixed case
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var lowered = str.toLowerCase()
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var uppered = str.toUpperCase()
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if (str !== lowered && str !== uppered) return 'Mixed-case string ' + str
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str = lowered
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var split = str.lastIndexOf('1')
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if (split === -1) return 'No separator character for ' + str
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if (split === 0) return 'Missing prefix for ' + str
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var prefix = str.slice(0, split)
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var wordChars = str.slice(split + 1)
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if (wordChars.length < 6) return 'Data too short'
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var chk = prefixChk(prefix)
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if (typeof chk === 'string') return chk
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var words = []
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for (var i = 0; i < wordChars.length; ++i) {
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var c = wordChars.charAt(i)
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var v = ALPHABET_MAP[c]
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if (v === undefined) return 'Unknown character ' + c
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chk = polymodStep(chk) ^ v
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// not in the checksum?
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if (i + 6 >= wordChars.length) continue
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words.push(v)
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}
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if (chk !== 1) return 'Invalid checksum for ' + str
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return { prefix: prefix, words: words }
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}
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function decodeUnsafe () {
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var res = __decode.apply(null, arguments)
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if (typeof res === 'object') return res
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}
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function decode (str) {
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var res = __decode.apply(null, arguments)
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if (typeof res === 'object') return res
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throw new Error(res)
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}
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function convert (data, inBits, outBits, pad) {
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var value = 0
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var bits = 0
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var maxV = (1 << outBits) - 1
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var result = []
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for (var i = 0; i < data.length; ++i) {
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value = (value << inBits) | data[i]
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bits += inBits
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while (bits >= outBits) {
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bits -= outBits
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result.push((value >> bits) & maxV)
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}
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}
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if (pad) {
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if (bits > 0) {
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result.push((value << (outBits - bits)) & maxV)
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}
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} else {
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if (bits >= inBits) return 'Excess padding'
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if ((value << (outBits - bits)) & maxV) return 'Non-zero padding'
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}
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return result
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}
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function toWordsUnsafe (bytes) {
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var res = convert(bytes, 8, 5, true)
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if (Array.isArray(res)) return res
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}
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function toWords (bytes) {
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var res = convert(bytes, 8, 5, true)
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if (Array.isArray(res)) return res
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throw new Error(res)
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}
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function fromWordsUnsafe (words) {
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var res = convert(words, 5, 8, false)
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if (Array.isArray(res)) return res
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}
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function fromWords (words) {
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var res = convert(words, 5, 8, false)
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if (Array.isArray(res)) return res
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throw new Error(res)
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}
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module.exports = {
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decodeUnsafe: decodeUnsafe,
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decode: decode,
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encode: encode,
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toWordsUnsafe: toWordsUnsafe,
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toWords: toWords,
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fromWordsUnsafe: fromWordsUnsafe,
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fromWords: fromWords
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}
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