github.com/bananabytelabs/wazero@v0.0.0-20240105073314-54b22a776da8/internal/wasm/binary/global.go (about)

     1  package binary
     2  
     3  import (
     4  	"bytes"
     5  	"fmt"
     6  
     7  	"github.com/bananabytelabs/wazero/api"
     8  	"github.com/bananabytelabs/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
    14  func 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
    27  func 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  }