github.com/phillinzzz/newBsc@v1.1.6/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  const (
    20  	set2BitsMask = uint16(0b1100_0000_0000_0000)
    21  	set3BitsMask = uint16(0b1110_0000_0000_0000)
    22  	set4BitsMask = uint16(0b1111_0000_0000_0000)
    23  	set5BitsMask = uint16(0b1111_1000_0000_0000)
    24  	set6BitsMask = uint16(0b1111_1100_0000_0000)
    25  	set7BitsMask = uint16(0b1111_1110_0000_0000)
    26  )
    27  
    28  // bitvec is a bit vector which maps bytes in a program.
    29  // An unset bit means the byte is an opcode, a set bit means
    30  // it's data (i.e. argument of PUSHxx).
    31  type bitvec []byte
    32  
    33  var lookup = [8]byte{
    34  	0x80, 0x40, 0x20, 0x10, 0x8, 0x4, 0x2, 0x1,
    35  }
    36  
    37  func (bits bitvec) set1(pos uint64) {
    38  	bits[pos/8] |= lookup[pos%8]
    39  }
    40  
    41  func (bits bitvec) setN(flag uint16, pos uint64) {
    42  	a := flag >> (pos % 8)
    43  	bits[pos/8] |= byte(a >> 8)
    44  	if b := byte(a); b != 0 {
    45  		//	If the bit-setting affects the neighbouring byte, we can assign - no need to OR it,
    46  		//	since it's the first write to that byte
    47  		bits[pos/8+1] = b
    48  	}
    49  }
    50  
    51  func (bits bitvec) set8(pos uint64) {
    52  	a := byte(0xFF >> (pos % 8))
    53  	bits[pos/8] |= a
    54  	bits[pos/8+1] = ^a
    55  }
    56  
    57  func (bits bitvec) set16(pos uint64) {
    58  	a := byte(0xFF >> (pos % 8))
    59  	bits[pos/8] |= a
    60  	bits[pos/8+1] = 0xFF
    61  	bits[pos/8+2] = ^a
    62  }
    63  
    64  // codeSegment checks if the position is in a code segment.
    65  func (bits *bitvec) codeSegment(pos uint64) bool {
    66  	return ((*bits)[pos/8] & (0x80 >> (pos % 8))) == 0
    67  }
    68  
    69  // codeBitmap collects data locations in code.
    70  func codeBitmap(code []byte) bitvec {
    71  	// The bitmap is 4 bytes longer than necessary, in case the code
    72  	// ends with a PUSH32, the algorithm will push zeroes onto the
    73  	// bitvector outside the bounds of the actual code.
    74  	bits := make(bitvec, len(code)/8+1+4)
    75  	return codeBitmapInternal(code, bits)
    76  }
    77  
    78  // codeBitmapInternal is the internal implementation of codeBitmap.
    79  // It exists for the purpose of being able to run benchmark tests
    80  // without dynamic allocations affecting the results.
    81  func codeBitmapInternal(code, bits bitvec) bitvec {
    82  	for pc := uint64(0); pc < uint64(len(code)); {
    83  		op := OpCode(code[pc])
    84  		pc++
    85  		if op < PUSH1 || op > PUSH32 {
    86  			continue
    87  		}
    88  		numbits := op - PUSH1 + 1
    89  		if numbits >= 8 {
    90  			for ; numbits >= 16; numbits -= 16 {
    91  				bits.set16(pc)
    92  				pc += 16
    93  			}
    94  			for ; numbits >= 8; numbits -= 8 {
    95  				bits.set8(pc)
    96  				pc += 8
    97  			}
    98  		}
    99  		switch numbits {
   100  		case 1:
   101  			bits.set1(pc)
   102  			pc += 1
   103  		case 2:
   104  			bits.setN(set2BitsMask, pc)
   105  			pc += 2
   106  		case 3:
   107  			bits.setN(set3BitsMask, pc)
   108  			pc += 3
   109  		case 4:
   110  			bits.setN(set4BitsMask, pc)
   111  			pc += 4
   112  		case 5:
   113  			bits.setN(set5BitsMask, pc)
   114  			pc += 5
   115  		case 6:
   116  			bits.setN(set6BitsMask, pc)
   117  			pc += 6
   118  		case 7:
   119  			bits.setN(set7BitsMask, pc)
   120  			pc += 7
   121  		}
   122  	}
   123  	return bits
   124  }