github.com/AlohaMobile/go-ethereum@v1.9.7/core/vm/analysis.go (about)

     1  // Copyright 2014 The go-ethereum Authors
     2  // This file is part of the go-ethereum library.
     3  //
     4  // The go-ethereum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The go-ethereum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  package vm
    18  
    19  // bitvec is a bit vector which maps bytes in a program.
    20  // An unset bit means the byte is an opcode, a set bit means
    21  // it's data (i.e. argument of PUSHxx).
    22  type bitvec []byte
    23  
    24  func (bits *bitvec) set(pos uint64) {
    25  	(*bits)[pos/8] |= 0x80 >> (pos % 8)
    26  }
    27  func (bits *bitvec) set8(pos uint64) {
    28  	(*bits)[pos/8] |= 0xFF >> (pos % 8)
    29  	(*bits)[pos/8+1] |= ^(0xFF >> (pos % 8))
    30  }
    31  
    32  // codeSegment checks if the position is in a code segment.
    33  func (bits *bitvec) codeSegment(pos uint64) bool {
    34  	return ((*bits)[pos/8] & (0x80 >> (pos % 8))) == 0
    35  }
    36  
    37  // codeBitmap collects data locations in code.
    38  func codeBitmap(code []byte) bitvec {
    39  	// The bitmap is 4 bytes longer than necessary, in case the code
    40  	// ends with a PUSH32, the algorithm will push zeroes onto the
    41  	// bitvector outside the bounds of the actual code.
    42  	bits := make(bitvec, len(code)/8+1+4)
    43  	for pc := uint64(0); pc < uint64(len(code)); {
    44  		op := OpCode(code[pc])
    45  
    46  		if op >= PUSH1 && op <= PUSH32 {
    47  			numbits := op - PUSH1 + 1
    48  			pc++
    49  			for ; numbits >= 8; numbits -= 8 {
    50  				bits.set8(pc) // 8
    51  				pc += 8
    52  			}
    53  			for ; numbits > 0; numbits-- {
    54  				bits.set(pc)
    55  				pc++
    56  			}
    57  		} else {
    58  			pc++
    59  		}
    60  	}
    61  	return bits
    62  }