EIP-145: Bitwise shifting instructions in EVM Source

作者 Alex Beregszaszi, Paweł Bylica
状态 Final
类型 Standards Track
分类 Core
创建日期 2017-02-13
英文版 https://eips.ethereum.org/EIPS/eip-145

目录

简述

To provide native bitwise shifting with cost on par with other arithmetic operations.

Abstract

Native bitwise shifting instructions are introduced, which are more efficient processing wise on the host and are cheaper to use by a contract.

Motivation

EVM is lacking bitwise shifting operators, but supports other logical and arithmetic operators. Shift operations can be implemented via arithmetic operators, but that has a higher cost and requires more processing time from the host. Implementing SHL and SHR using arithmetic cost each 35 gas, while the proposed instructions take 3 gas.

Specification

The following instructions are introduced:

0x1b: SHL (shift left)

The SHL instruction (shift left) pops 2 values from the stack, first arg1 and then arg2, and pushes on the stack arg2 shifted to the left by arg1 number of bits. The result is equal to

(arg2 * 2^arg1) mod 2^256

Notes:

  • The value (arg2) is interpreted as an unsigned number.
  • The shift amount (arg1) is interpreted as an unsigned number.
  • If the shift amount (arg1) is greater or equal 256 the result is 0.
  • This is equivalent to PUSH1 2 EXP MUL.

0x1c: SHR (logical shift right)

The SHR instruction (logical shift right) pops 2 values from the stack, first arg1 and then arg2, and pushes on the stack arg2 shifted to the right by arg1 number of bits with zero fill. The result is equal to

floor(arg2 / 2^arg1)

Notes:

  • The value (arg2) is interpreted as an unsigned number.
  • The shift amount (arg1) is interpreted as an unsigned number.
  • If the shift amount (arg1) is greater or equal 256 the result is 0.
  • This is equivalent to PUSH1 2 EXP DIV.

0x1d: SAR (arithmetic shift right)

The SAR instruction (arithmetic shift right) pops 2 values from the stack, first arg1 and then arg2, and pushes on the stack arg2 shifted to the right by arg1 number of bits with sign extension. The result is equal to

floor(arg2 / 2^arg1)

注意:

  • The value (arg2) is interpreted as a signed number.
  • The shift amount (arg1) is interpreted as an unsigned number.
  • If the shift amount (arg1) is greater or equal 256 the result is 0 if arg2 is non-negative or -1 if arg2 is negative.
  • This is not equivalent to PUSH1 2 EXP SDIV, since it rounds differently. See SDIV(-1, 2) == 0, while SAR(-1, 1) == -1.

The cost of the shift instructions is set at verylow tier (3 gas).

Rationale

Instruction operands were chosen to fit the more natural use case of shifting a value already on the stack. This means the operand order is swapped compared to most arithmetic insturctions.

向后兼容性

The newly introduced instructions have no effect on bytecode created in the past.

测试用例

SHL (shift left)

  1. ``` PUSH 0x0000000000000000000000000000000000000000000000000000000000000001 PUSH 0x00 SHL

    0x0000000000000000000000000000000000000000000000000000000000000001 ```

  2. PUSH 0x0000000000000000000000000000000000000000000000000000000000000001
PUSH 0x01
SHL
---
0x0000000000000000000000000000000000000000000000000000000000000002

  3. ``` PUSH 0x0000000000000000000000000000000000000000000000000000000000000001 PUSH 0xff SHL

    0x8000000000000000000000000000000000000000000000000000000000000000 ```

  4. PUSH 0x0000000000000000000000000000000000000000000000000000000000000001
PUSH 0x0100
SHL
---
0x0000000000000000000000000000000000000000000000000000000000000000

  5. ``` PUSH 0x0000000000000000000000000000000000000000000000000000000000000001 PUSH 0x0101 SHL

    0x0000000000000000000000000000000000000000000000000000000000000000 ```

  6. PUSH 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
PUSH 0x00
SHL
---
0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff

  7. ``` PUSH 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff PUSH 0x01 SHL

    0xfffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffe ```

  8. PUSH 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
PUSH 0xff
SHL
---
0x8000000000000000000000000000000000000000000000000000000000000000

  9. ``` PUSH 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff PUSH 0x0100 SHL

    0x0000000000000000000000000000000000000000000000000000000000000000 ```

  10. PUSH 0x0000000000000000000000000000000000000000000000000000000000000000
PUSH 0x01
SHL
---
0x0000000000000000000000000000000000000000000000000000000000000000
  11. PUSH 0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff PUSH 0x01 SHL --- 0xfffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffe

SHR (logical shift right) 

  1. PUSH 0x0000000000000000000000000000000000000000000000000000000000000001
PUSH 0x00
SHR
---
0x0000000000000000000000000000000000000000000000000000000000000001

  2. ``` PUSH 0x0000000000000000000000000000000000000000000000000000000000000001 PUSH 0x01 SHR

    0x0000000000000000000000000000000000000000000000000000000000000000 ```

  3. PUSH 0x8000000000000000000000000000000000000000000000000000000000000000
PUSH 0x01
SHR
---
0x4000000000000000000000000000000000000000000000000000000000000000

  4. ``` PUSH 0x8000000000000000000000000000000000000000000000000000000000000000 PUSH 0xff SHR

    0x0000000000000000000000000000000000000000000000000000000000000001 ```

  5. PUSH 0x8000000000000000000000000000000000000000000000000000000000000000
PUSH 0x0100
SHR
---
0x0000000000000000000000000000000000000000000000000000000000000000

  6. ``` PUSH 0x8000000000000000000000000000000000000000000000000000000000000000 PUSH 0x0101 SHR

    0x0000000000000000000000000000000000000000000000000000000000000000 ```

  7. PUSH 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
PUSH 0x00
SHR
---
0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff

  8. ``` PUSH 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff PUSH 0x01 SHR

    0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff ```

  9. PUSH 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
PUSH 0xff
SHR
---
0x0000000000000000000000000000000000000000000000000000000000000001
  10. PUSH 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff PUSH 0x0100 SHR --- 0x0000000000000000000000000000000000000000000000000000000000000000 
  11. PUSH 0x0000000000000000000000000000000000000000000000000000000000000000
PUSH 0x01
SHR
---
0x0000000000000000000000000000000000000000000000000000000000000000

SAR (arithmetic shift right)

  1. ``` PUSH 0x0000000000000000000000000000000000000000000000000000000000000001 PUSH 0x00 SAR

    0x0000000000000000000000000000000000000000000000000000000000000001 ```

  2. PUSH 0x0000000000000000000000000000000000000000000000000000000000000001
PUSH 0x01
SAR
---
0x0000000000000000000000000000000000000000000000000000000000000000

  3. ``` PUSH 0x8000000000000000000000000000000000000000000000000000000000000000 PUSH 0x01 SAR

    0xc000000000000000000000000000000000000000000000000000000000000000 ```

  4. PUSH 0x8000000000000000000000000000000000000000000000000000000000000000
PUSH 0xff
SAR
---
0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff

  5. ``` PUSH 0x8000000000000000000000000000000000000000000000000000000000000000 PUSH 0x0100 SAR

    0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff ```

  6. PUSH 0x8000000000000000000000000000000000000000000000000000000000000000
PUSH 0x0101
SAR
---
0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff

  7. ``` PUSH 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff PUSH 0x00 SAR

    0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff ```

  8. PUSH 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
PUSH 0x01
SAR
---
0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff

  9. ``` PUSH 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff PUSH 0xff SAR

    0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff ```

  10. PUSH 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
PUSH 0x0100
SAR
---
0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
  11. PUSH 0x0000000000000000000000000000000000000000000000000000000000000000 PUSH 0x01 SAR --- 0x0000000000000000000000000000000000000000000000000000000000000000 
  12. PUSH 0x4000000000000000000000000000000000000000000000000000000000000000
PUSH 0xfe
SAR
---
0x0000000000000000000000000000000000000000000000000000000000000001
  13. PUSH 0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff PUSH 0xf8 SAR --- 0x000000000000000000000000000000000000000000000000000000000000007f 
  14. PUSH 0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
PUSH 0xfe
SAR
---
0x0000000000000000000000000000000000000000000000000000000000000001
  15. PUSH 0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff PUSH 0xff SAR --- 0x0000000000000000000000000000000000000000000000000000000000000000 
  16. PUSH 0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
PUSH 0x0100
SAR
---
0x0000000000000000000000000000000000000000000000000000000000000000

Implementation

Client support:

  • cpp-ethereum: https://github.com/ethereum/cpp-ethereum/pull/4054

Compiler support:

  • Solidity/LLL: https://github.com/ethereum/solidity/pull/2541

测试

Sources:

  • https://github.com/ethereum/tests/tree/develop/src/GeneralStateTestsFiller/stShift

Filled Tests:

  • https://github.com/ethereum/tests/tree/develop/GeneralStateTests/stShift
  • https://github.com/ethereum/tests/tree/develop/BlockchainTests/GeneralStateTests/stShift

Copyright and related rights waived via CC0.

参考文献

Please cite this document as:

Alex Beregszaszi, Paweł Bylica, "EIP-145: Bitwise shifting instructions in EVM," Ethereum Improvement Proposals, no. 145, February 2017. [Online serial]. Available: https://eips.ethereum.org/EIPS/eip-145.