element.go

Documentation: github.com/tetratelabs/wazero/internal/testing/binaryencoding

     1  package binaryencoding
     2  
     3  import (
     4  	"bytes"
     5  	"fmt"
     6  
     7  	"github.com/tetratelabs/wazero/internal/leb128"
     8  	"github.com/tetratelabs/wazero/internal/wasm"
     9  )
    10  
    11  func ensureElementKindFuncRef(r *bytes.Reader) error {
    12  	elemKind, err := r.ReadByte()
    13  	if err != nil {
    14  		return fmt.Errorf("read element prefix: %w", err)
    15  	}
    16  	if elemKind != 0x0 { // ElemKind is fixed to 0x0 now: https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/binary/modules.html#element-section
    17  		return fmt.Errorf("element kind must be zero but was 0x%x", elemKind)
    18  	}
    19  	return nil
    20  }
    21  
    22  // encodeCode returns the wasm.ElementSegment encoded in WebAssembly 1.0 (20191205) Binary Format.
    23  //
    24  // https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#element-section%E2%91%A0
    25  func encodeElement(e *wasm.ElementSegment) (ret []byte) {
    26  	if e.Mode == wasm.ElementModeActive {
    27  		ret = append(ret, leb128.EncodeInt32(int32(e.TableIndex))...)
    28  		ret = append(ret, encodeConstantExpression(e.OffsetExpr)...)
    29  		ret = append(ret, leb128.EncodeUint32(uint32(len(e.Init)))...)
    30  		for _, idx := range e.Init {
    31  			ret = append(ret, leb128.EncodeInt32(int32(idx))...)
    32  		}
    33  	} else {
    34  		panic("TODO: support encoding for non-active elements in bulk-memory-operations proposal")
    35  	}
    36  	return
    37  }
    38

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