Further optimize base64Write

Author: chjj

index.js

@@ -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
@@ -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