1package binary
 2
 3import (
 4	"bytes"
 5	"fmt"
 6
 7	"github.com/tetratelabs/wazero/api"
 8	"github.com/tetratelabs/wazero/internal/wasm"
 9)
10
11// decodeGlobal returns the api.Global decoded with the WebAssembly 1.0 (20191205) Binary Format.
12//
13// See https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#binary-global
14func decodeGlobal(r *bytes.Reader, enabledFeatures api.CoreFeatures, ret *wasm.Global) (err error) {
15	ret.Type, err = decodeGlobalType(r)
16	if err != nil {
17		return err
18	}
19
20	err = decodeConstantExpression(r, enabledFeatures, &ret.Init)
21	return
22}
23
24// decodeGlobalType returns the wasm.GlobalType decoded with the WebAssembly 1.0 (20191205) Binary Format.
25//
26// See https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#binary-globaltype
27func decodeGlobalType(r *bytes.Reader) (wasm.GlobalType, error) {
28	vt, err := decodeValueTypes(r, 1)
29	if err != nil {
30		return wasm.GlobalType{}, fmt.Errorf("read value type: %w", err)
31	}
32
33	ret := wasm.GlobalType{
34		ValType: vt[0],
35	}
36
37	b, err := r.ReadByte()
38	if err != nil {
39		return wasm.GlobalType{}, fmt.Errorf("read mutablity: %w", err)
40	}
41
42	switch mut := b; mut {
43	case 0x00: // not mutable
44	case 0x01: // mutable
45		ret.Mutable = true
46	default:
47		return wasm.GlobalType{}, fmt.Errorf("%w for mutability: %#x != 0x00 or 0x01", ErrInvalidByte, mut)
48	}
49	return ret, nil
50}