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59 lines
1.8 KiB
59 lines
1.8 KiB
const Mode = require('./mode')
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/**
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* Array of characters available in alphanumeric mode
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*
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* As per QR Code specification, to each character
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* is assigned a value from 0 to 44 which in this case coincides
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* with the array index
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*
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* @type {Array}
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*/
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const ALPHA_NUM_CHARS = [
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'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
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'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
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'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
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' ', '$', '%', '*', '+', '-', '.', '/', ':'
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]
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function AlphanumericData (data) {
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this.mode = Mode.ALPHANUMERIC
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this.data = data
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}
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AlphanumericData.getBitsLength = function getBitsLength (length) {
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return 11 * Math.floor(length / 2) + 6 * (length % 2)
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}
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AlphanumericData.prototype.getLength = function getLength () {
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return this.data.length
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}
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AlphanumericData.prototype.getBitsLength = function getBitsLength () {
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return AlphanumericData.getBitsLength(this.data.length)
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}
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AlphanumericData.prototype.write = function write (bitBuffer) {
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let i
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// Input data characters are divided into groups of two characters
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// and encoded as 11-bit binary codes.
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for (i = 0; i + 2 <= this.data.length; i += 2) {
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// The character value of the first character is multiplied by 45
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let value = ALPHA_NUM_CHARS.indexOf(this.data[i]) * 45
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// The character value of the second digit is added to the product
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value += ALPHA_NUM_CHARS.indexOf(this.data[i + 1])
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// The sum is then stored as 11-bit binary number
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bitBuffer.put(value, 11)
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}
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// If the number of input data characters is not a multiple of two,
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// the character value of the final character is encoded as a 6-bit binary number.
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if (this.data.length % 2) {
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bitBuffer.put(ALPHA_NUM_CHARS.indexOf(this.data[i]), 6)
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}
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}
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module.exports = AlphanumericData
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