ethereum.forks.bpo5.vm.stackethereum.forks.amsterdam.vm.stack

Ethereum Virtual Machine (EVM) Stack.

.. contents:: Table of Contents :backlinks: none :local:

Introduction

Implementation of the stack operators for the EVM.

decode_single

Decode the immediate byte for DUPN/SWAPN to get the stack index.

Return n with 17 <= n <= 235.

Parameters

x : int The immediate byte value (0-90 or 128-255).

Returns

int The stack index n, where 17 <= n <= 235.

Raises

InvalidParameter If x is in the forbidden range (90 < x < 128 or x > 255).

def decode_single(​x: U8​) -> U8:
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    <snip>
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    if not (U8(0) <= x <= U8(90) or U8(128) <= x <= U8(255)):
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        raise InvalidParameter(
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            f"DUPN/SWAPN immediate byte {x} is out of range. "
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            "Valid range: 0 <= x <= 90 or 128 <= x <= 255"
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        )
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    return U8((int(x) + 145) % 256)

decode_pair

Decode the immediate byte for EXCHANGE to get two stack indices.

Return (n, m) with 1 <= n <= 14 and n < m <= 30 - n.

Parameters

x : int The immediate byte value (0-81 or 128-255).

Returns

Tuple[int, int] The two stack indices (n, m), where 1 <= n <= 14 and n < m <= 30 - n.

Raises

InvalidParameter If x is in the forbidden range (81 < x < 128 or x > 255).

def decode_pair(​x: U8​) -> Tuple[U8, U8]:
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    <snip>
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    if not (U8(0) <= x <= U8(81) or U8(128) <= x <= U8(255)):
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        raise InvalidParameter(
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            f"EXCHANGE immediate byte {x} is in the forbidden "
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            "range 82 <= x <= 127\n"
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            "Valid range: 0 <= x <= 81 or 128 <= x <= 255"
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        )
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    k = U8(int(x) ^ 143)
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    q, r = divmod(k, U8(16))
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    if q < r:
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        return q + U8(1), r + U8(1)
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    else:
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        return r + U8(1), U8(29) - q

pop

Pops the top item off of stack.

Parameters

stack : EVM stack.

Returns

value : U256 The top element on the stack.

def pop(​stack: List[U256]​) -> U256:
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    <snip>
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    if len(stack) == 0:
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        raise StackUnderflowError
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    return stack.pop()

push

Pushes value onto stack.

Parameters

stack : EVM stack.

value : Item to be pushed onto stack.

def push(​stack: List[U256], ​​value: U256​) -> None:
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    <snip>
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    if len(stack) == 1024:
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        raise StackOverflowError
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    return stack.append(value)