index.js
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module.exports = to_utf8
var out = []
, col = []
, fcc = String.fromCharCode
, mask = [0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01]
, unmask = [
0x00
, 0x01
, 0x02 | 0x01
, 0x04 | 0x02 | 0x01
, 0x08 | 0x04 | 0x02 | 0x01
, 0x10 | 0x08 | 0x04 | 0x02 | 0x01
, 0x20 | 0x10 | 0x08 | 0x04 | 0x02 | 0x01
, 0x40 | 0x20 | 0x10 | 0x08 | 0x04 | 0x02 | 0x01
]
function to_utf8(bytes, start, end) {
start = start === undefined ? 0 : start
end = end === undefined ? bytes.length : end
var idx = 0
, hi = 0x80
, collecting = 0
, pos
, by
col.length =
out.length = 0
while(idx < bytes.length) {
by = bytes[idx]
if(!collecting && by & hi) {
pos = find_pad_position(by)
collecting += pos
if(pos < 8) {
col[col.length] = by & unmask[6 - pos]
}
} else if(collecting) {
col[col.length] = by & unmask[6]
--collecting
if(!collecting && col.length) {
out[out.length] = fcc(reduced(col, pos))
col.length = 0
}
} else {
out[out.length] = fcc(by)
}
++idx
}
if(col.length && !collecting) {
out[out.length] = fcc(reduced(col, pos))
col.length = 0
}
return out.join('')
}
function find_pad_position(byt) {
for(var i = 0; i < 7; ++i) {
if(!(byt & mask[i])) {
break
}
}
return i
}
function reduced(list) {
var out = 0
for(var i = 0, len = list.length; i < len; ++i) {
out |= list[i] << ((len - i - 1) * 6)
}
return out
}