path: root/core/vm/memory.go

// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package vm

import (
    "fmt"
    "math/big"

    "github.com/ethereum/go-ethereum/common/math"
)

// Memory implements a simple memory model for the ethereum virtual machine.
type Memory struct {
    store       []byte
    lastGasCost uint64
}

// NewMemory returns a new memory memory model.
func NewMemory() *Memory {
    return &Memory{}
}

// Set sets offset + size to value
func (m *Memory) Set(offset, size uint64, value []byte) {
    // It's possible the offset is greater than 0 and size equals 0. This is because
    // the calcMemSize (common.go) could potentially return 0 when size is zero (NO-OP)
    if size > 0 {
        // length of store may never be less than offset + size.
        // The store should be resized PRIOR to setting the memory
        if offset+size > uint64(len(m.store)) {
            panic("invalid memory: store empty")
        }
        copy(m.store[offset:offset+size], value)
    }
}

// Set32 sets the 32 bytes starting at offset to the value of val, left-padded with zeroes to
// 32 bytes.
func (m *Memory) Set32(offset uint64, val *big.Int) {
    // length of store may never be less than offset + size.
    // The store should be resized PRIOR to setting the memory
    if offset+32 > uint64(len(m.store)) {
        panic("invalid memory: store empty")
    }
    // Zero the memory area
    copy(m.store[offset:offset+32], []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0})
    // Fill in relevant bits
    math.ReadBits(val, m.store[offset:offset+32])
}

// Resize resizes the memory to size
func (m *Memory) Resize(size uint64) {
    if uint64(m.Len()) < size {
        m.store = append(m.store, make([]byte, size-uint64(m.Len()))...)
    }
}

// Get returns offset + size as a new slice
func (m *Memory) Get(offset, size int64) (cpy []byte) {
    if size == 0 {
        return nil
    }

    if len(m.store) > int(offset) {
        cpy = make([]byte, size)
        copy(cpy, m.store[offset:offset+size])

        return
    }

    return
}

// GetPtr returns the offset + size
func (m *Memory) GetPtr(offset, size int64) []byte {
    if size == 0 {
        return nil
    }

    if len(m.store) > int(offset) {
        return m.store[offset : offset+size]
    }

    return nil
}

// Len returns the length of the backing slice
func (m *Memory) Len() int {
    return len(m.store)
}

// Data returns the backing slice
func (m *Memory) Data() []byte {
    return m.store
}

// Print dumps the content of the memory.
func (m *Memory) Print() {
    fmt.Printf("### mem %d bytes ###\n", len(m.store))
    if len(m.store) > 0 {
        addr := 0
        for i := 0; i+32 <= len(m.store); i += 32 {
            fmt.Printf("%03d: % x\n", addr, m.store[i:i+32])
            addr++
        }
    } else {
        fmt.Println("-- empty --")
    }
    fmt.Println("####################")
}