encoding optimizations

optimize.patch

diff --git a/src/encoding/base64/base64.go b/src/encoding/base64/base64.go
index ad3abe6..bff443f 100644
--- a/src/encoding/base64/base64.go
+++ b/src/encoding/base64/base64.go
@@ -22,7 +22,7 @@ import (
 // (RFC 1421).  RFC 4648 also defines an alternate encoding, which is
 // the standard encoding with - and _ substituted for + and /.
 type Encoding struct {
-	encode    string
+	encode    [64]byte
 	decodeMap [256]byte
 }
 
@@ -33,7 +33,10 @@ const encodeURL = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz012345678
 // which must be a 64-byte string.
 func NewEncoding(encoder string) *Encoding {
 	e := new(Encoding)
-	e.encode = encoder
+
+	for i, b := range encoder {
+		e.encode[i] = byte(b)
+	}
 	for i := 0; i < len(e.decodeMap); i++ {
 		e.decodeMap[i] = 0xFF
 	}
@@ -73,42 +76,38 @@ func (enc *Encoding) Encode(dst, src []byte) {
 		return
 	}
 
-	for len(src) > 0 {
-		var b0, b1, b2, b3 byte
+	di, si := 0, 0
+	N := (len(src) / 3) * 3
+	for si < N {
+		val := uint(src[si+0])<<16 | uint(src[si+1])<<8 | uint(src[si+2])
 
-		// Unpack 4x 6-bit source blocks into a 4 byte
-		// destination quantum
-		switch len(src) {
-		default:
-			b3 = src[2] & 0x3F
-			b2 = src[2] >> 6
-			fallthrough
-		case 2:
-			b2 |= (src[1] << 2) & 0x3F
-			b1 = src[1] >> 4
-			fallthrough
-		case 1:
-			b1 |= (src[0] << 4) & 0x3F
-			b0 = src[0] >> 2
-		}
+		dst[di+0] = enc.encode[val>>18]
+		dst[di+1] = enc.encode[val>>12&0x3F]
+		dst[di+2] = enc.encode[val>>6&0x3F]
+		dst[di+3] = enc.encode[val&0x3F]
 
-		// Encode 6-bit blocks using the base64 alphabet
-		dst[0] = enc.encode[b0]
-		dst[1] = enc.encode[b1]
-		dst[2] = enc.encode[b2]
-		dst[3] = enc.encode[b3]
-
-		// Pad the final quantum
-		if len(src) < 3 {
-			dst[3] = '='
-			if len(src) < 2 {
-				dst[2] = '='
-			}
-			break
+		si += 3
+		di += 4
+	}
+
+	remain := len(src) - si
+	if remain > 0 {
+		val := uint(src[si+0]) << 16
+		if remain == 2 {
+			val |= uint(src[si+1]) << 8
 		}
 
-		src = src[3:]
-		dst = dst[4:]
+		dst[di+0] = enc.encode[val>>18]
+		dst[di+1] = enc.encode[val>>12&0x3f]
+
+		switch remain {
+		case 2:
+			dst[di+2] = enc.encode[val>>6&0x3f]
+			dst[di+3] = '='
+		case 1:
+			dst[di+2] = '='
+			dst[di+3] = '='
+		}
 	}
 }