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 user 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 arithmetics 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, `arg1` and `arg2`, and pushes on the stack the second popped value `arg2` shifted to the left by the number of bits in the first popped value `arg1`. The result is equal to
```
(arg2 * 2^arg1) mod 2^256
```
Notes:
- If the shift amount is greater or equal 256 the result is 0.
### `0x1c`: `SHR` (logical shift right)
The `SHR` instruction (logical shift right) pops 2 values from the stack, `arg1` and `arg2`, and pushes on the stack the second popped value `arg2` shifted to the right by the number of bits in the first popped value `arg1` with zero fill. The result is equal to
```
arg2 udiv 2^arg1
```
Notes:
- If the shift amount is greater or equal 256 the result is 0.
### `0x1d`: `SAR` (arithmetic shift right)
The `SAR` instruction (arithmetic shift right) pops 2 values from the stack, `arg1` and `arg2`, and pushes on the stack the second popped value `arg2` shifted to the right by the number of bits in the first popped value `arg1` with sign extension. The result is equal to
```
arg2 sdiv 2^arg1
```
Notes:
-`arg1` is interpreted as unsigned number.
- If the shift amount is greater or equal 256 the result is 0 if `arg2` is non-negative or -1 if `arg2` is negative.
