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Overview

Opcode: 0x63 Introduced: Frontier (EVM genesis) PUSH4 pushes a 4-byte immediate value from the bytecode onto the stack. The 4 bytes immediately following the opcode are read and zero-padded to 256 bits.

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Specification

Stack Input: 
[]
Stack Output: 
value (uint256, 4 bytes from bytecode)
Gas Cost: 3 (GasFastestStep) Bytecode: 1 byte opcode + 4 bytes immediate data Operation: 
value = read_bytes(pc + 1, 4)  // Big-endian
stack.push(value)
pc += 5

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Behavior

PUSH4 reads 4 bytes from bytecode starting at position pc + 1, interprets them as a big-endian unsigned integer, and pushes the result onto the stack. Key characteristics:
  • Reads exactly 4 bytes following opcode
  • Big-endian byte order (most significant byte first)
  • Zero-padded to 256 bits if less than 32 bytes
  • InvalidOpcode if insufficient bytecode remaining
  • PC advances by 5 (opcode + data)

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Examples

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Basic Usage

import { handler_0x63_PUSH4 } from '@tevm/voltaire/evm/stack/handlers';
import { createFrame } from '@tevm/voltaire/evm/Frame';

// Bytecode with PUSH4
const bytecode = new Uint8Array([
  0x63,  // PUSH4
  0x01, 0x02, 0x03, 0x04   // 4 bytes: 01020304
]);

const frame = createFrame({
  bytecode,
  pc: 0,
  stack: [],
  gasRemaining: 1000n
});

const err = handler_0x63_PUSH4(frame);

console.log(frame.stack); // [0x0102030400000000000000000000000000000000000000000000000000000000n]
console.log(frame.pc); // 5
console.log(frame.gasRemaining); // 997n (3 gas consumed)

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Solidity Compilation

contract Example {
    // Function selectors use PUSH4
    function transfer() public {
        // PUSH4 0xa9059cbb  (4-byte selector)
    }
}

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Assembly Usage

assembly {
    // Push 4-byte value
    push4 0xffffffff
    
    // Example: function selector
}

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Gas Cost

Cost: 3 gas (GasFastestStep) All PUSH1-32 instructions cost the same despite different data sizes. Bytecode size impact:
  • PUSH4: 5 bytes (1 opcode + 4 data)
  • PUSH32: 33 bytes (1 opcode + 32 data)
Comparison:
OpcodeGasBytesUse Case
PUSH021Zero constant (Shanghai+)
PUSH132Small numbers (0-255)
PUSH435Function selectors

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Common Usage

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Function Selectors

// Function selector is first 4 bytes of keccak256("transfer(address,uint256)")
function checkSelector() public pure {
    assembly {
        let selector := shr(224, calldataload(0))
        push4 0xa9059cbb  // transfer selector
        eq  // Compare
    }
}

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Big-Endian Encoding

// Bytecode: PUSH4 01 02 03 04
// Reads as: 0x01020304

// Most significant byte first
// Byte 0: 0x01 (highest significance)
// Byte 3: 0x04 (lowest significance)

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Implementation

/**
 * Read immediate data from bytecode for PUSH operations
 */
function readImmediate(bytecode: Uint8Array, pc: number, size: number): bigint | null {
  if (pc + 1 + size > bytecode.length) {
    return null;
  }

  let result = 0n;
  for (let i = 0; i < size; i++) {
    result = (result << 8n) | BigInt(bytecode[pc + 1 + i]);
  }
  return result;
}

/**
 * PUSH4 opcode (0x63) - Push 4 bytes onto stack
 *
 * Stack: [] => [value]
 * Gas: 3 (GasFastestStep)
 */
export function handler_0x63_PUSH4(frame: FrameType): EvmError | null {
  const gasErr = consumeGas(frame, FastestStep);
  if (gasErr) return gasErr;

  const value = readImmediate(frame.bytecode, frame.pc, 4);
  if (value === null) {
    return { type: "InvalidOpcode" };
  }

  const pushErr = pushStack(frame, value);
  if (pushErr) return pushErr;

  frame.pc += 5;
  return null;
}

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Edge Cases

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Insufficient Bytecode

// Bytecode ends before 4 bytes read
const bytecode = new Uint8Array([0x63, 0x01]); // Only 1 byte instead of 4
const frame = createFrame({ bytecode, pc: 0 });

const err = handler_0x63_PUSH4(frame);
console.log(err); // { type: "InvalidOpcode" }

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Stack Overflow

// Stack at maximum capacity
const frame = createFrame({
  stack: new Array(1024).fill(0n),
  bytecode: new Uint8Array([0x63, 0x00, 0x00, 0x00, 0x00])
});

const err = handler_0x63_PUSH4(frame);
console.log(err); // { type: "StackOverflow" }

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Out of Gas

// Insufficient gas
const frame = createFrame({
  gasRemaining: 2n,  // Need 3 gas
  bytecode: new Uint8Array([0x63, 0xff, 0xff, 0xff, 0xff])
});

const err = handler_0x63_PUSH4(frame);
console.log(err); // { type: "OutOfGas" }

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Maximum Value

// All bytes 0xFF
const bytecode = new Uint8Array([0x63, 0xff, 0xff, 0xff, 0xff]);
const frame = createFrame({ bytecode, pc: 0 });

handler_0x63_PUSH4(frame);
console.log(frame.stack[0]); // 0xffffffff00000000000000000000000000000000000000000000000000000000n

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References