Repository navigation
Expand file tree
/
Copy pathsizes.go
More file actions
138 lines (128 loc) · 2.7 KB
/
Copy pathsizes.go
File metadata and controls
138 lines (128 loc) · 2.7 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
// 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 := range n {
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 := range n {
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
}