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// Copyright 2013 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 interp
// Emulated functions that we cannot interpret because they are
// external or because they use "unsafe" or "reflect" operations.
import (
type externalFn func(fr *frame, args []value) value
// TODO(adonovan): fix: reflect.Value abstracts an lvalue or an
// rvalue; Set() causes mutations that can be observed via aliases.
// We have not captured that correctly here.
// Key strings are from Function.String().
var externals = make(map[string]externalFn)
func init() {
// That little dot ۰ is an Arabic zero numeral (U+06F0), categories [Nd].
for k, v := range map[string]externalFn{
"(reflect.Value).Bool": ext۰reflect۰Value۰Bool,
"(reflect.Value).CanAddr": ext۰reflect۰Value۰CanAddr,
"(reflect.Value).CanInterface": ext۰reflect۰Value۰CanInterface,
"(reflect.Value).Elem": ext۰reflect۰Value۰Elem,
"(reflect.Value).Field": ext۰reflect۰Value۰Field,
"(reflect.Value).Float": ext۰reflect۰Value۰Float,
"(reflect.Value).Index": ext۰reflect۰Value۰Index,
"(reflect.Value).Int": ext۰reflect۰Value۰Int,
"(reflect.Value).Interface": ext۰reflect۰Value۰Interface,
"(reflect.Value).IsNil": ext۰reflect۰Value۰IsNil,
"(reflect.Value).IsValid": ext۰reflect۰Value۰IsValid,
"(reflect.Value).Kind": ext۰reflect۰Value۰Kind,
"(reflect.Value).Len": ext۰reflect۰Value۰Len,
"(reflect.Value).MapIndex": ext۰reflect۰Value۰MapIndex,
"(reflect.Value).MapKeys": ext۰reflect۰Value۰MapKeys,
"(reflect.Value).NumField": ext۰reflect۰Value۰NumField,
"(reflect.Value).NumMethod": ext۰reflect۰Value۰NumMethod,
"(reflect.Value).Pointer": ext۰reflect۰Value۰Pointer,
"(reflect.Value).Set": ext۰reflect۰Value۰Set,
"(reflect.Value).String": ext۰reflect۰Value۰String,
"(reflect.Value).Type": ext۰reflect۰Value۰Type,
"(reflect.Value).Uint": ext۰reflect۰Value۰Uint,
"(reflect.error).Error": ext۰reflect۰error۰Error,
"(reflect.rtype).Bits": ext۰reflect۰rtype۰Bits,
"(reflect.rtype).Elem": ext۰reflect۰rtype۰Elem,
"(reflect.rtype).Field": ext۰reflect۰rtype۰Field,
"(reflect.rtype).In": ext۰reflect۰rtype۰In,
"(reflect.rtype).Kind": ext۰reflect۰rtype۰Kind,
"(reflect.rtype).NumField": ext۰reflect۰rtype۰NumField,
"(reflect.rtype).NumIn": ext۰reflect۰rtype۰NumIn,
"(reflect.rtype).NumMethod": ext۰reflect۰rtype۰NumMethod,
"(reflect.rtype).NumOut": ext۰reflect۰rtype۰NumOut,
"(reflect.rtype).Out": ext۰reflect۰rtype۰Out,
"(reflect.rtype).Size": ext۰reflect۰rtype۰Size,
"(reflect.rtype).String": ext۰reflect۰rtype۰String,
"bytes.Equal": ext۰bytes۰Equal,
"bytes.IndexByte": ext۰bytes۰IndexByte,
"fmt.Sprint": ext۰fmt۰Sprint,
"math.Abs": ext۰math۰Abs,
"math.Exp": ext۰math۰Exp,
"math.Float32bits": ext۰math۰Float32bits,
"math.Float32frombits": ext۰math۰Float32frombits,
"math.Float64bits": ext۰math۰Float64bits,
"math.Float64frombits": ext۰math۰Float64frombits,
"math.Inf": ext۰math۰Inf,
"math.IsNaN": ext۰math۰IsNaN,
"math.Ldexp": ext۰math۰Ldexp,
"math.Log": ext۰math۰Log,
"math.Min": ext۰math۰Min,
"math.NaN": ext۰math۰NaN,
"os.Exit": ext۰os۰Exit,
"os.Getenv": ext۰os۰Getenv,
"reflect.New": ext۰reflect۰New,
"reflect.SliceOf": ext۰reflect۰SliceOf,
"reflect.TypeOf": ext۰reflect۰TypeOf,
"reflect.ValueOf": ext۰reflect۰ValueOf,
"reflect.Zero": ext۰reflect۰Zero,
"runtime.Breakpoint": ext۰runtime۰Breakpoint,
"runtime.GC": ext۰runtime۰GC,
"runtime.GOMAXPROCS": ext۰runtime۰GOMAXPROCS,
"runtime.GOROOT": ext۰runtime۰GOROOT,
"runtime.Goexit": ext۰runtime۰Goexit,
"runtime.Gosched": ext۰runtime۰Gosched,
"runtime.NumCPU": ext۰runtime۰NumCPU,
"strings.Count": ext۰strings۰Count,
"strings.Index": ext۰strings۰Index,
"strings.IndexByte": ext۰strings۰IndexByte,
"strings.Replace": ext۰strings۰Replace,
"time.Sleep": ext۰time۰Sleep,
"unicode/utf8.DecodeRuneInString": ext۰unicode۰utf8۰DecodeRuneInString,
} {
externals[k] = v
func ext۰bytes۰Equal(fr *frame, args []value) value {
// func Equal(a, b []byte) bool
a := args[0].([]value)
b := args[1].([]value)
if len(a) != len(b) {
return false
for i := range a {
if a[i] != b[i] {
return false
return true
func ext۰bytes۰IndexByte(fr *frame, args []value) value {
// func IndexByte(s []byte, c byte) int
s := args[0].([]value)
c := args[1].(byte)
for i, b := range s {
if b.(byte) == c {
return i
return -1
func ext۰math۰Float64frombits(fr *frame, args []value) value {
return math.Float64frombits(args[0].(uint64))
func ext۰math۰Float64bits(fr *frame, args []value) value {
return math.Float64bits(args[0].(float64))
func ext۰math۰Float32frombits(fr *frame, args []value) value {
return math.Float32frombits(args[0].(uint32))
func ext۰math۰Abs(fr *frame, args []value) value {
return math.Abs(args[0].(float64))
func ext۰math۰Exp(fr *frame, args []value) value {
return math.Exp(args[0].(float64))
func ext۰math۰Float32bits(fr *frame, args []value) value {
return math.Float32bits(args[0].(float32))
func ext۰math۰Min(fr *frame, args []value) value {
return math.Min(args[0].(float64), args[1].(float64))
func ext۰math۰NaN(fr *frame, args []value) value {
return math.NaN()
func ext۰math۰IsNaN(fr *frame, args []value) value {
return math.IsNaN(args[0].(float64))
func ext۰math۰Inf(fr *frame, args []value) value {
return math.Inf(args[0].(int))
func ext۰math۰Ldexp(fr *frame, args []value) value {
return math.Ldexp(args[0].(float64), args[1].(int))
func ext۰math۰Log(fr *frame, args []value) value {
return math.Log(args[0].(float64))
func ext۰runtime۰Breakpoint(fr *frame, args []value) value {
return nil
func ext۰strings۰Count(fr *frame, args []value) value {
return strings.Count(args[0].(string), args[1].(string))
func ext۰strings۰IndexByte(fr *frame, args []value) value {
return strings.IndexByte(args[0].(string), args[1].(byte))
func ext۰strings۰Index(fr *frame, args []value) value {
return strings.Index(args[0].(string), args[1].(string))
func ext۰strings۰Replace(fr *frame, args []value) value {
// func Replace(s, old, new string, n int) string
s := args[0].(string)
new := args[1].(string)
old := args[2].(string)
n := args[3].(int)
return strings.Replace(s, old, new, n)
func ext۰runtime۰GOMAXPROCS(fr *frame, args []value) value {
// Ignore args[0]; don't let the interpreted program
// set the interpreter's GOMAXPROCS!
return runtime.GOMAXPROCS(0)
func ext۰runtime۰Goexit(fr *frame, args []value) value {
// TODO(adonovan): don't kill the interpreter's main goroutine.
return nil
func ext۰runtime۰GOROOT(fr *frame, args []value) value {
return runtime.GOROOT()
func ext۰runtime۰GC(fr *frame, args []value) value {
return nil
func ext۰runtime۰Gosched(fr *frame, args []value) value {
return nil
func ext۰runtime۰NumCPU(fr *frame, args []value) value {
return runtime.NumCPU()
func ext۰time۰Sleep(fr *frame, args []value) value {
return nil
func valueToBytes(v value) []byte {
in := v.([]value)
b := make([]byte, len(in))
for i := range in {
b[i] = in[i].(byte)
return b
func ext۰os۰Getenv(fr *frame, args []value) value {
name := args[0].(string)
switch name {
return "1"
case "GOARCH":
return "amd64"
case "GOOS":
return "linux"
return os.Getenv(name)
func ext۰os۰Exit(fr *frame, args []value) value {
func ext۰unicode۰utf8۰DecodeRuneInString(fr *frame, args []value) value {
r, n := utf8.DecodeRuneInString(args[0].(string))
return tuple{r, n}
// A fake function for turning an arbitrary value into a string.
// Handles only the cases needed by the tests.
// Uses same logic as 'print' built-in.
func ext۰fmt۰Sprint(fr *frame, args []value) value {
buf := new(bytes.Buffer)
wasStr := false
for i, arg := range args[0].([]value) {
x := arg.(iface).v
_, isStr := x.(string)
if i > 0 && !wasStr && !isStr {
buf.WriteByte(' ')
wasStr = isStr
return buf.String()