Golang hash function

gistfile1.go

// https://play.golang.org/p/auAxrJQ1b1
package main

import (
	"fmt"
	"reflect"
	"unsafe"
)

type rtype struct {
	size       uintptr
	ptrdata    uintptr  // number of bytes in the type that can contain pointers
	hash       uint32   // hash of type; avoids computation in hash tables
	tflag      uint8    // extra type information flags
	align      uint8    // alignment of variable with this type
	fieldAlign uint8    // alignment of struct field with this type
	kind       uint8    // enumeration for C
	alg        *typeAlg // algorithm table
	gcdata     *byte    // garbage collection data
	str        int32    // string form
	ptrToThis  int32    // type for pointer to this type, may be zero
}

// a copy of runtime.typeAlg
type typeAlg struct {
	hash  func(unsafe.Pointer, uintptr) uintptr
	equal func(unsafe.Pointer, unsafe.Pointer) bool
}

type iface struct {
	tab  uintptr
	data unsafe.Pointer
}

func getalgs(example interface{}, seed uintptr) (hash func(in interface{}) uintptr, equal func(a, b interface{}) bool) {

	typ := reflect.ValueOf(reflect.TypeOf(example))
	rt := *(*rtype)(unsafe.Pointer(typ.Pointer()))
	alg := rt.alg
	origiface := *(*iface)(unsafe.Pointer(&example))
	origitab := origiface.tab
	hash = func(in interface{}) uintptr {
		is := *(*iface)(unsafe.Pointer(uintptr(unsafe.Pointer(&in))))
		if is.tab != origitab {
			panic("wrong type")
		}
		return alg.hash(is.data, seed)
	}
	equal = func(a, b interface{}) bool {
		leftiface := *(*iface)(unsafe.Pointer(&a))
		rightiface := *(*iface)(unsafe.Pointer(&a))
		if leftiface.tab != origitab || rightiface.tab != origitab {
			panic("wrong type")
		}
		return alg.equal(leftiface.data, rightiface.data)
	}
	return
}

func main() {
	hash, equal := getalgs(2, 0)
	fmt.Println(hash(4))
	hash(1)
	fmt.Println(equal(*new(int), *new(int)))
}