42 lines
1.0 KiB
JavaScript
42 lines
1.0 KiB
JavaScript
'use strict'
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// Reverse of
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// http://plantuml.sourceforge.net/codejavascript2.html
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// It is described as being "a transformation close to base64"
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// The code has been slightly modified to pass linters
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function decode6bit (cc) {
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var c = cc.charCodeAt(0)
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if (cc === '_') return 63
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if (cc === '-') return 62
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if (c >= 97) return c - 61 // - 97 + 26 + 10
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if (c >= 65) return c - 55 // - 65 + 10
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if (c >= 48) return c - 48
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return '?'
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}
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function extract3bytes (data) {
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var c1 = decode6bit(data[0])
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var c2 = decode6bit(data[1])
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var c3 = decode6bit(data[2])
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var c4 = decode6bit(data[3])
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var b1 = c1 << 2 | (c2 >> 4) & 0x3F
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var b2 = (c2 << 4) & 0xF0 | (c3 >> 2) & 0xF
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var b3 = (c3 << 6) & 0xC0 | c4 & 0x3F
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return [b1, b2, b3]
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}
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module.exports = function (data) {
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var r = ''
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var i = 0
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for (i = 0; i < data.length; i += 4) {
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var t = extract3bytes(data.substring(i, i + 4))
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r = r + String.fromCharCode(t[0])
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r = r + String.fromCharCode(t[1])
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r = r + String.fromCharCode(t[2])
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}
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return r
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}
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