1package binary
 2
 3import (
 4	"bytes"
 5	"fmt"
 6
 7	"github.com/tetratelabs/wazero/internal/leb128"
 8)
 9
10// decodeLimitsType returns the `limitsType` (min, max) decoded with the WebAssembly 1.0 (20191205) Binary Format.
11//
12// See https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#limits%E2%91%A6
13//
14// Extended in threads proposal: https://webassembly.github.io/threads/core/binary/types.html#limits
15func decodeLimitsType(r *bytes.Reader) (min uint32, max *uint32, shared bool, err error) {
16	var flag byte
17	if flag, err = r.ReadByte(); err != nil {
18		err = fmt.Errorf("read leading byte: %v", err)
19		return
20	}
21
22	switch flag {
23	case 0x00, 0x02:
24		min, _, err = leb128.DecodeUint32(r)
25		if err != nil {
26			err = fmt.Errorf("read min of limit: %v", err)
27		}
28	case 0x01, 0x03:
29		min, _, err = leb128.DecodeUint32(r)
30		if err != nil {
31			err = fmt.Errorf("read min of limit: %v", err)
32			return
33		}
34		var m uint32
35		if m, _, err = leb128.DecodeUint32(r); err != nil {
36			err = fmt.Errorf("read max of limit: %v", err)
37		} else {
38			max = &m
39		}
40	default:
41		err = fmt.Errorf("%v for limits: %#x not in (0x00, 0x01, 0x02, 0x03)", ErrInvalidByte, flag)
42	}
43
44	shared = flag == 0x02 || flag == 0x03
45
46	return
47}