go const 源码
golang const 代码
文件路径：/src/cmd/compile/internal/ir/const.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 ir
import (
"go/constant"
"math"
"math/big"
"cmd/compile/internal/base"
"cmd/compile/internal/types"
)
func NewBool(b bool) Node {
return NewLiteral(constant.MakeBool(b))
}
func NewInt(v int64) Node {
return NewLiteral(constant.MakeInt64(v))
}
func NewString(s string) Node {
return NewLiteral(constant.MakeString(s))
}
const (
// Maximum size in bits for big.Ints before signaling
// overflow and also mantissa precision for big.Floats.
ConstPrec = 512
)
func BigFloat(v constant.Value) *big.Float {
f := new(big.Float)
f.SetPrec(ConstPrec)
switch u := constant.Val(v).(type) {
case int64:
f.SetInt64(u)
case *big.Int:
f.SetInt(u)
case *big.Float:
f.Set(u)
case *big.Rat:
f.SetRat(u)
default:
base.Fatalf("unexpected: %v", u)
}
return f
}
// ConstOverflow reports whether constant value v is too large
// to represent with type t.
func ConstOverflow(v constant.Value, t *types.Type) bool {
switch {
case t.IsInteger():
bits := uint(8 * t.Size())
if t.IsUnsigned() {
x, ok := constant.Uint64Val(v)
return !ok || x>>bits != 0
}
x, ok := constant.Int64Val(v)
if x < 0 {
x = ^x
}
return !ok || x>>(bits-1) != 0
case t.IsFloat():
switch t.Size() {
case 4:
f, _ := constant.Float32Val(v)
return math.IsInf(float64(f), 0)
case 8:
f, _ := constant.Float64Val(v)
return math.IsInf(f, 0)
}
case t.IsComplex():
ft := types.FloatForComplex(t)
return ConstOverflow(constant.Real(v), ft) || ConstOverflow(constant.Imag(v), ft)
}
base.Fatalf("ConstOverflow: %v, %v", v, t)
panic("unreachable")
}
// IsConstNode reports whether n is a Go language constant (as opposed to a
// compile-time constant).
//
// Expressions derived from nil, like string([]byte(nil)), while they
// may be known at compile time, are not Go language constants.
func IsConstNode(n Node) bool {
return n.Op() == OLITERAL
}
func IsSmallIntConst(n Node) bool {
if n.Op() == OLITERAL {
v, ok := constant.Int64Val(n.Val())
return ok && int64(int32(v)) == v
}
return false
}
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