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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 gcsizes provides a types.Sizes implementation that adheres
// to the rules used by the gc compiler.
package gcsizes
import (
"go/build"
"go/types"
)
type Sizes struct {
WordSize int64
MaxAlign int64
}
// ForArch returns a correct Sizes for the given architecture.
func ForArch(arch string) *Sizes {
wordSize := int64(8)
maxAlign := int64(8)
switch build.Default.GOARCH {
case "386", "arm":
wordSize, maxAlign = 4, 4
case "amd64p32":
wordSize = 4
}
return &Sizes{WordSize: wordSize, MaxAlign: maxAlign}
}
func (s *Sizes) Alignof(T types.Type) int64 {
switch t := T.Underlying().(type) {
case *types.Array:
return s.Alignof(t.Elem())
case *types.Struct:
max := int64(1)
n := t.NumFields()
var fields []*types.Var
for i := 0; i < n; i++ {
fields = append(fields, t.Field(i))
}
for _, f := range fields {
if a := s.Alignof(f.Type()); a > max {
max = a
}
}
return max
}
a := s.Sizeof(T) // may be 0
if a < 1 {
return 1
}
if a > s.MaxAlign {
return s.MaxAlign
}
return a
}
func (s *Sizes) Offsetsof(fields []*types.Var) []int64 {
offsets := make([]int64, len(fields))
var o int64
for i, f := range fields {
a := s.Alignof(f.Type())
o = align(o, a)
offsets[i] = o
o += s.Sizeof(f.Type())
}
return offsets
}
var basicSizes = [...]byte{
types.Bool: 1,
types.Int8: 1,
types.Int16: 2,
types.Int32: 4,
types.Int64: 8,
types.Uint8: 1,
types.Uint16: 2,
types.Uint32: 4,
types.Uint64: 8,
types.Float32: 4,
types.Float64: 8,
types.Complex64: 8,
types.Complex128: 16,
}
func (s *Sizes) Sizeof(T types.Type) int64 {
switch t := T.Underlying().(type) {
case *types.Basic:
k := t.Kind()
if int(k) < len(basicSizes) {
if s := basicSizes[k]; s > 0 {
return int64(s)
}
}
if k == types.String {
return s.WordSize * 2
}
case *types.Array:
n := t.Len()
if n == 0 {
return 0
}
a := s.Alignof(t.Elem())
z := s.Sizeof(t.Elem())
return align(z, a)*(n-1) + z
case *types.Slice:
return s.WordSize * 3
case *types.Struct:
n := t.NumFields()
if n == 0 {
return 0
}
var fields []*types.Var
for i := 0; i < n; i++ {
fields = append(fields, t.Field(i))
}
offsets := s.Offsetsof(fields)
a := s.Alignof(T)
lsz := s.Sizeof(fields[n-1].Type())
if lsz == 0 {
lsz = 1
}
z := offsets[n-1] + lsz
return align(z, a)
case *types.Interface:
return s.WordSize * 2
}
return s.WordSize // catch-all
}
// align returns the smallest y >= x such that y % a == 0.
func align(x, a int64) int64 {
y := x + a - 1
return y - y%a
}
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