github.com/MetalBlockchain/subnet-evm@v0.4.9/core/vm/memory.go (about)

     1  // (c) 2019-2020, Ava Labs, Inc.
     2  //
     3  // This file is a derived work, based on the go-ethereum library whose original
     4  // notices appear below.
     5  //
     6  // It is distributed under a license compatible with the licensing terms of the
     7  // original code from which it is derived.
     8  //
     9  // Much love to the original authors for their work.
    10  // **********
    11  // Copyright 2015 The go-ethereum Authors
    12  // This file is part of the go-ethereum library.
    13  //
    14  // The go-ethereum library is free software: you can redistribute it and/or modify
    15  // it under the terms of the GNU Lesser General Public License as published by
    16  // the Free Software Foundation, either version 3 of the License, or
    17  // (at your option) any later version.
    18  //
    19  // The go-ethereum library is distributed in the hope that it will be useful,
    20  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    21  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    22  // GNU Lesser General Public License for more details.
    23  //
    24  // You should have received a copy of the GNU Lesser General Public License
    25  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    26  
    27  package vm
    28  
    29  import (
    30  	"github.com/holiman/uint256"
    31  )
    32  
    33  // Memory implements a simple memory model for the ethereum virtual machine.
    34  type Memory struct {
    35  	store       []byte
    36  	lastGasCost uint64
    37  }
    38  
    39  // NewMemory returns a new memory model.
    40  func NewMemory() *Memory {
    41  	return &Memory{}
    42  }
    43  
    44  // Set sets offset + size to value
    45  func (m *Memory) Set(offset, size uint64, value []byte) {
    46  	// It's possible the offset is greater than 0 and size equals 0. This is because
    47  	// the calcMemSize (common.go) could potentially return 0 when size is zero (NO-OP)
    48  	if size > 0 {
    49  		// length of store may never be less than offset + size.
    50  		// The store should be resized PRIOR to setting the memory
    51  		if offset+size > uint64(len(m.store)) {
    52  			panic("invalid memory: store empty")
    53  		}
    54  		copy(m.store[offset:offset+size], value)
    55  	}
    56  }
    57  
    58  // Set32 sets the 32 bytes starting at offset to the value of val, left-padded with zeroes to
    59  // 32 bytes.
    60  func (m *Memory) Set32(offset uint64, val *uint256.Int) {
    61  	// length of store may never be less than offset + size.
    62  	// The store should be resized PRIOR to setting the memory
    63  	if offset+32 > uint64(len(m.store)) {
    64  		panic("invalid memory: store empty")
    65  	}
    66  	// Fill in relevant bits
    67  	b32 := val.Bytes32()
    68  	copy(m.store[offset:], b32[:])
    69  }
    70  
    71  // Resize resizes the memory to size
    72  func (m *Memory) Resize(size uint64) {
    73  	if uint64(m.Len()) < size {
    74  		m.store = append(m.store, make([]byte, size-uint64(m.Len()))...)
    75  	}
    76  }
    77  
    78  // GetCopy returns offset + size as a new slice
    79  func (m *Memory) GetCopy(offset, size int64) (cpy []byte) {
    80  	if size == 0 {
    81  		return nil
    82  	}
    83  
    84  	if len(m.store) > int(offset) {
    85  		cpy = make([]byte, size)
    86  		copy(cpy, m.store[offset:offset+size])
    87  
    88  		return
    89  	}
    90  
    91  	return
    92  }
    93  
    94  // GetPtr returns the offset + size
    95  func (m *Memory) GetPtr(offset, size int64) []byte {
    96  	if size == 0 {
    97  		return nil
    98  	}
    99  
   100  	if len(m.store) > int(offset) {
   101  		return m.store[offset : offset+size]
   102  	}
   103  
   104  	return nil
   105  }
   106  
   107  // Len returns the length of the backing slice
   108  func (m *Memory) Len() int {
   109  	return len(m.store)
   110  }
   111  
   112  // Data returns the backing slice
   113  func (m *Memory) Data() []byte {
   114  	return m.store
   115  }