code review 125720044: runtime: use better hash for non-empty interface

src/pkg/runtime/alg.go

 // Copyright 2014 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 runtime
 
 import "unsafe"
 
 const (
         c0 = uintptr((8-uint64(ptrSize))/4*2860486313 + (uint64(ptrSize)-4)/4*33054211828000289)
@@ skipping 93 matching lines @@
         return f64hash(&x[1], 4, f64hash(&x[0], 4, h))
 }
 
 func nohash(a unsafe.Pointer, s uintptr, h uintptr) uintptr {
         panic(errorString("hash of unhashable type"))
 }
 
 func interhash(a *interface {
         f()
 }, s uintptr, h uintptr) uintptr {
-        return 0
+        tab := (*iface)(unsafe.Pointer(a)).tab
+        if tab == nil {
+                return h
+        }
+        t := tab._type
+        fn := goalg(t.alg).hash
+        if **(**uintptr)(unsafe.Pointer(&fn)) == nohashcode {
+                // calling nohash will panic too,
+                // but we can print a better error.
+                panic(errorString("hash of unhashable type " + *t._string))
+        }
+        if uintptr(t.size) <= ptrSize {
+                return c1 * fn(unsafe.Pointer(&(*eface)(unsafe.Pointer(a)).data), uintptr(t.size), h^c0)
+        } else {
+                return c1 * fn((*eface)(unsafe.Pointer(a)).data, uintptr(t.size), h^c0)
+        }
 }
 
 func nilinterhash(a *interface{}, s uintptr, h uintptr) uintptr {
         t := (*eface)(unsafe.Pointer(a))._type
         if t == nil {
                 return h
         }
         fn := goalg(t.alg).hash
         if **(**uintptr)(unsafe.Pointer(&fn)) == nohashcode {
                 // calling nohash will panic too,
@@ skipping 21 matching lines @@
         return goalg(&algarray[alg_MEM]).hash(*(*unsafe.Pointer)(unsafe.Pointer(&b)), uintptr(len(b)), seed)
 }
 
 func int32Hash(i uint32, seed uintptr) uintptr {
         return goalg(&algarray[alg_MEM32]).hash(noescape(unsafe.Pointer(&i)), 4, seed)
 }
 
 func int64Hash(i uint64, seed uintptr) uintptr {
         return goalg(&algarray[alg_MEM64]).hash(noescape(unsafe.Pointer(&i)), 8, seed)
 }