github.com/onflow/flow-go@v0.35.7-crescendo-preview.23-atree-inlining/fvm/evm/emulator/state/code.go (about)

     1  package state
     2  
     3  import (
     4  	"encoding/binary"
     5  	"fmt"
     6  )
     7  
     8  // CodeContainer contains codes and keeps
     9  // track of reference counts
    10  type CodeContainer struct {
    11  	code []byte
    12  	// keeping encoded so we can reuse it later
    13  	buffer   []byte
    14  	refCount uint64
    15  }
    16  
    17  // NewCodeContainer constructs a new code container
    18  func NewCodeContainer(code []byte) *CodeContainer {
    19  	return &CodeContainer{
    20  		code:     code,
    21  		refCount: 1,
    22  	}
    23  }
    24  
    25  // CodeContainerFromEncoded constructs a code container from the encoded data
    26  func CodeContainerFromEncoded(encoded []byte) (*CodeContainer, error) {
    27  	if len(encoded) < 8 {
    28  		return nil, fmt.Errorf("invalid length for the encoded code container")
    29  	}
    30  	return &CodeContainer{
    31  		refCount: binary.BigEndian.Uint64(encoded[:8]),
    32  		buffer:   encoded, // keep encoded as buffer for future use
    33  		code:     encoded[8:],
    34  	}, nil
    35  }
    36  
    37  // Code returns the code part of the code container
    38  func (cc *CodeContainer) Code() []byte {
    39  	return cc.code
    40  }
    41  
    42  // RefCount returns the ref count
    43  func (cc *CodeContainer) RefCount() uint64 {
    44  	return cc.refCount
    45  }
    46  
    47  // IncRefCount increment the ref count
    48  func (cc *CodeContainer) IncRefCount() {
    49  	cc.refCount++
    50  }
    51  
    52  // DecRefCount decrement the ref count and
    53  // returns true if the ref has reached to zero
    54  func (cc *CodeContainer) DecRefCount() bool {
    55  	// check if ref is already zero
    56  	// this condition should never happen
    57  	// but better to be here to prevent underflow
    58  	if cc.refCount == 0 {
    59  		return true
    60  	}
    61  	cc.refCount--
    62  	return cc.refCount == 0
    63  }
    64  
    65  // Encoded returns the encoded content of the code container
    66  func (cc *CodeContainer) Encode() []byte {
    67  	// try using the buffer if possible to avoid
    68  	// extra allocations
    69  	encodedLen := 8 + len(cc.code)
    70  	var encoded []byte
    71  	if len(cc.buffer) < encodedLen {
    72  		encoded = make([]byte, encodedLen)
    73  	} else {
    74  		encoded = cc.buffer[:encodedLen]
    75  	}
    76  	binary.BigEndian.PutUint64(encoded[:8], cc.refCount)
    77  	copy(encoded[8:], cc.code)
    78  	return encoded
    79  }