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convert.js
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convert.js
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'use strict'
const ba = require('binascii')
function dec2bin(dec){
return (dec >>> 0).toString(2)
}
// Javascript left shift operator only works on 32 bit numbers
function leftShift(number, shift) {
return number * Math.pow(2, shift)
}
function rightShift(number, shift) {
return number / Math.pow(2, shift)
}
var word_size = 32
var word_mask = leftShift(1, word_size)-1
module.exports = {
expand_array: function (inp, out_len, bit_len) {
var byte_pad = 0
if (bit_len < 8 || word_size < 7+bit_len) {
return
}
var bit_len_mask = leftShift(1, bit_len)-1
var out_width = Math.floor((bit_len+7)/8) + byte_pad
if (out_len != 8*out_width*inp.length/bit_len) {
console.log('88888')
return
}
var out = new Buffer(out_len)
var acc_bits = 0
var acc_value = 0
var j = 0
for (var i = 0; i < inp.length; i++) {
acc_value = (leftShift(acc_value, 8) & word_mask) | inp[i]
// getting negative values here, could be the bitwise ops on 32 bits only in js
acc_bits += 8
if (acc_bits >= bit_len) {
acc_bits -= bit_len
for (var x = byte_pad; x < out_width; x++) {
out[j+x] = (Math.floor(rightShift(acc_value, (acc_bits+(8*(out_width-x-1)))))) & ((Math.floor(rightShift(bit_len_mask, (8*(out_width-x-1))))) & 0xFF)
}
j += out_width
}
}
return out
},
compress_array: function (inp, out_len, bit_len) {
var byte_pad = 0
if (bit_len < 8 || word_size < 7+bit_len) {
return
}
var in_width = Math.floor((bit_len+7)/8) + byte_pad
if (out_len != Math.floor(8*in_width*inp.length/bit_len)) {
return
}
var out = new Buffer(out_len)
var bit_len_mask = leftShift(1, bit_len)-1
var acc_bits = 0
var acc_value = 0
var j = 0
for (var i = 0; i < out_len; i++) {
if (acc_bits < 8) {
acc_value = (leftShift(acc_value, bit_len) & word_mask) | inp[j]
for (var x = byte_pad; x < in_width; x++) {
acc_value = acc_value | (
leftShift((inp[j+x] & ((rightShift(bit_len_mask, (8*(in_width-x-1)))) & 0xFF)), (8*(in_width-x-1)))
)
}
j += in_width
acc_bits += bit_len
}
acc_bits -= 8
out[i] = (rightShift(acc_value, acc_bits)) & 0xFF
}
return out
}
}