go-ethereum/core/vm/analysis.go

package vm

import (
	"math/big"

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

var bigMaxUint64 = new(big.Int).SetUint64(^uint64(0))

// destinations stores one map per contract (keyed by hash of code).
// The maps contain an entry for each location of a JUMPDEST
// instruction.
type destinations map[common.Hash]map[uint64]struct{}

// has checks whether code has a JUMPDEST at dest.
func (d destinations) has(codehash common.Hash, code []byte, dest *big.Int) bool {
	// PC cannot go beyond len(code) and certainly can't be bigger than 64bits.
	// Don't bother checking for JUMPDEST in that case.
	if dest.Cmp(bigMaxUint64) > 0 {
		return false
	}
	m, analysed := d[codehash]
	if !analysed {
		m = jumpdests(code)
		d[codehash] = m
	}
	_, ok := m[dest.Uint64()]
	return ok
}

// jumpdests creates a map that contains an entry for each
// PC location that is a JUMPDEST instruction.
func jumpdests(code []byte) map[uint64]struct{} {
	m := make(map[uint64]struct{})
	for pc := uint64(0); pc < uint64(len(code)); pc++ {
		var op OpCode = OpCode(code[pc])
		switch op {
		case PUSH1, PUSH2, PUSH3, PUSH4, PUSH5, PUSH6, PUSH7, PUSH8, PUSH9, PUSH10, PUSH11, PUSH12, PUSH13, PUSH14, PUSH15, PUSH16, PUSH17, PUSH18, PUSH19, PUSH20, PUSH21, PUSH22, PUSH23, PUSH24, PUSH25, PUSH26, PUSH27, PUSH28, PUSH29, PUSH30, PUSH31, PUSH32:
			a := uint64(op) - uint64(PUSH1) + 1
			pc += a
		case JUMPDEST:
			m[pc] = struct{}{}
		}
	}
	return m
}