code review 5448065: Add a []byte argument to hash.Hash to allow an allocati...

src/pkg/crypto/md5/md5.go

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // Package md5 implements the MD5 hash algorithm as defined in RFC 1321.
 package md5
 
 import (
         "crypto"
         "hash"
@@ skipping 59 matching lines @@
                 p = p[n:]
         }
         n := _Block(d, p)
         p = p[n:]
         if len(p) > 0 {
                 d.nx = copy(d.x[:], p)
         }
         return
 }
 
-func (d0 *digest) Sum() []byte {
+func (d0 *digest) Sum(in []byte) []byte {
         // Make a copy of d0 so that caller can keep writing and summing.
         d := new(digest)
         *d = *d0
 
         // Padding.  Add a 1 bit and 0 bits until 56 bytes mod 64.
         len := d.len
         var tmp [64]byte
         tmp[0] = 0x80
         if len%64 < 56 {
                 d.Write(tmp[0 : 56-len%64])
         } else {
                 d.Write(tmp[0 : 64+56-len%64])
         }
 
         // Length in bits.
         len <<= 3
         for i := uint(0); i < 8; i++ {
                 tmp[i] = byte(len >> (8 * i))
         }
         d.Write(tmp[0:8])
 
         if d.nx != 0 {
                 panic("d.nx != 0")
         }
 
-        p := make([]byte, 16)
-        j := 0
         for _, s := range d.s {
-                p[j+0] = byte(s >> 0)
-                p[j+1] = byte(s >> 8)
-                p[j+2] = byte(s >> 16)
-                p[j+3] = byte(s >> 24)
-                j += 4
+                in = append(in, byte(s>>0))
+                in = append(in, byte(s>>8))
+                in = append(in, byte(s>>16))
+                in = append(in, byte(s>>24))
         }
-        return p
+        return in
 }