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68 lines
1.4 KiB
68 lines
1.4 KiB
5 years ago
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'use strict'
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var Buffer = require('safe-buffer').Buffer
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var max = 65536
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var cache = {}
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function generateBuffer (i) {
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var buffer = Buffer.allocUnsafe(2)
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buffer.writeUInt8(i >> 8, 0)
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buffer.writeUInt8(i & 0x00FF, 0 + 1)
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return buffer
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}
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function generateCache () {
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for (var i = 0; i < max; i++) {
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cache[i] = generateBuffer(i)
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}
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}
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/**
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* calcVariableByteIntLength - calculate the variable byte integer
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* length field
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*
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* @api private
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*/
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function calcVariableByteIntLength (length) {
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if (length >= 0 && length < 128) return 1
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else if (length >= 128 && length < 16384) return 2
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else if (length >= 16384 && length < 2097152) return 3
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else if (length >= 2097152 && length < 268435456) return 4
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else return 0
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}
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function genBufVariableByteInt (num) {
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var digit = 0
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var pos = 0
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var length = calcVariableByteIntLength(num)
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var buffer = Buffer.allocUnsafe(length)
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do {
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digit = num % 128 | 0
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num = num / 128 | 0
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if (num > 0) digit = digit | 0x80
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buffer.writeUInt8(digit, pos++)
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} while (num > 0)
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return {
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data: buffer,
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length: length
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}
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}
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function generate4ByteBuffer (num) {
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var buffer = Buffer.allocUnsafe(4)
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buffer.writeUInt32BE(num, 0)
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return buffer
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}
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module.exports = {
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cache: cache,
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generateCache: generateCache,
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generateNumber: generateBuffer,
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genBufVariableByteInt: genBufVariableByteInt,
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generate4ByteBuffer: generate4ByteBuffer
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}
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