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Further optimize base64Write
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chjj committed Feb 5, 2024
1 parent 0a0b942 commit 42bc6ba
Showing 1 changed file with 49 additions and 20 deletions.
69 changes: 49 additions & 20 deletions index.js
Original file line number Diff line number Diff line change
Expand Up @@ -1019,36 +1019,59 @@ function asciiWrite (buf, string, offset, length) {
}

function base64Write (buf, string, offset, length) {
const src = string.replace(/[^+/0-9A-Za-z-_=]/g, '')
const eq = src.indexOf('=')
const src = string
const dst = buf

let srcLen = eq >= 0 ? eq : src.length
let srcLen = src.length
let srcPos = 0
let dstLen = length
let dstPos = offset
let invalid = false

if (srcLen > 0 && src[srcLen - 1] === '=') srcLen -= 1
if (srcLen > 0 && src[srcLen - 1] === '=') srcLen -= 1

retry: for (;;) { // eslint-disable-line
while (srcLen >= 4 && dstLen >= 3) {
const c1 = src.charCodeAt(srcPos++)
const c2 = src.charCodeAt(srcPos++)
const c3 = src.charCodeAt(srcPos++)
const c4 = src.charCodeAt(srcPos++)
const t1 = base64Table[c1 & 0x7f]
const t2 = base64Table[c2 & 0x7f]
const t3 = base64Table[c3 & 0x7f]
const t4 = base64Table[c4 & 0x7f]

if ((c1 | c2 | c3 | c4 | t1 | t2 | t3 | t4) & ~0x7f) {
srcPos -= 4
invalid = true // Slow parsing until we recover.
break
}

while (srcLen >= 4 && dstLen >= 3) {
const t1 = base64Table[src.charCodeAt(srcPos++)]
const t2 = base64Table[src.charCodeAt(srcPos++)]
const t3 = base64Table[src.charCodeAt(srcPos++)]
const t4 = base64Table[src.charCodeAt(srcPos++)]

dst[dstPos++] = (t1 << 2) | (t2 >> 4)
dst[dstPos++] = (t2 << 4) | (t3 >> 2)
dst[dstPos++] = (t3 << 6) | (t4 >> 0)
dst[dstPos++] = (t1 << 2) | (t2 >> 4)
dst[dstPos++] = (t2 << 4) | (t3 >> 2)
dst[dstPos++] = (t3 << 6) | (t4 >> 0)

srcLen -= 4
dstLen -= 3
}
srcLen -= 4
dstLen -= 3
}

{
let w1, w2, w3, w4
let state = 0

while (srcLen && dstLen) {
const w = base64Table[src.charCodeAt(srcPos)]
const c = src.charCodeAt(srcPos)
const w = base64Table[c & 0x7f]

srcPos++
srcLen--

switch (srcPos & 3) {
if ((c | w) & ~0x7f) {
if (c === 0x3d) break // Stop on `=`
continue // Skip invalid
}

switch (state & 3) {
case 0:
w1 = w
break
Expand All @@ -1066,12 +1089,18 @@ function base64Write (buf, string, offset, length) {
w4 = w
dst[dstPos++] = (w3 << 6) | (w4 >> 0)
dstLen--
if (invalid) {
// Retry fast parsing.
invalid = false
continue retry // eslint-disable-line
}
break
}

srcPos++
srcLen--
state++
}

break
}

return dstPos - offset
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