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Swap shift operands (value is the top item)

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Alex Beregszaszi 2017-04-23 14:53:46 +01:00
parent 0b3461651f
commit 7bc447717f
1 changed files with 8 additions and 8 deletions
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16
EIPS/eip-draft_bitwise_shifts.md
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@ -27,10 +27,10 @@ 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
The `SHL` instruction (shift left) pops 2 values from the stack, `arg1` and `arg2`, and pushes on the stack the first popped value `arg1` shifted to the left by the number of bits in the second popped value `arg2`. The result is equal to
```
(arg2 * 2^arg1) mod 2^256
(arg1 * 2^arg2) mod 2^256
```
Notes:
@ -38,10 +38,10 @@ Notes:
### `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
The `SHR` instruction (logical shift right) pops 2 values from the stack, `arg1` and `arg2`, and pushes on the stack the first popped value `arg1` shifted to the right by the number of bits in the second popped value `arg2` with zero fill. The result is equal to
```
arg2 udiv 2^arg1
arg1 udiv 2^arg2
```
Notes:
@ -49,15 +49,15 @@ Notes:
### `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
The `SAR` instruction (arithmetic shift right) pops 2 values from the stack, `arg1` and `arg2`, and pushes on the stack the first popped value `arg1` shifted to the right by the number of bits in the second popped value `arg2` with sign extension. The result is equal to
```
arg2 sdiv 2^arg1
arg1 sdiv 2^arg2
```
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.
- `arg2` is interpreted as unsigned number.
- If the shift amount (`arg2`) is greater or equal 256 the result is 0 if `arg1` is non-negative or -1 if `arg1` is negative.
The cost of the shift instructions is set at `verylow` tier (3 gas).