> ## Documentation Index
> Fetch the complete documentation index at: https://voltaire.tevm.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# DUP4 (0x83)

> Duplicate 4th stack item

<Warning>
  **This page is a placeholder.** All examples on this page are currently AI-generated and are not correct. This documentation will be completed in the future with accurate, tested examples.
</Warning>

## Overview

**Opcode:** `0x83`
**Introduced:** Frontier (EVM genesis)

DUP4 duplicates the 4th stack item and pushes it to the top of the stack. The original 4th item remains in place.

## Specification

**Stack Input:**

```
[..., value, item3, ..., item1]
```

**Stack Output:**

```
[..., value, item3, ..., item1, value]
```

**Gas Cost:** 3 (GasFastestStep)

**Operation:**

```
value = stack[depth - 4]
stack.push(value)
```

## Behavior

DUP4 copies the 4th-from-top stack item without removing it. Requires stack depth ≥ 4.

Key characteristics:

* Requires stack depth ≥ 4
* Original value unchanged
* New copy pushed to top
* StackUnderflow if depth \< 4
* Stack depth increases by 1

## Examples

### Basic Usage

```typescript theme={null}
import { handler_0x83_DUP4 } from '@tevm/voltaire/evm/stack/handlers';
import { createFrame } from '@tevm/voltaire/evm/Frame';

// Duplicate 4th item
const frame = createFrame({
  stack: [400n, 300n, 200n, 100n],
  gasRemaining: 1000n
});

const err = handler_0x83_DUP4(frame);

console.log(frame.stack); // [400n, 300n, 200n, 100n, 100n] - 4th item duplicated
console.log(frame.gasRemaining); // 997n (3 gas consumed)
```

### Solidity Compilation

```solidity theme={null}
contract Example {
    function deepAccess() public pure {
        // Access deep stack value
        assembly {
            // Stack has 4 items
            dup4  // Duplicate 4th item to top
        }
    }
}
```

### Assembly Usage

```solidity theme={null}
assembly {
    push1 0x01
    push1 0x02
    push1 0x03
    push1 0x04
    // Stack: [0x01, 0x02, 0x03, 0x04]

    dup4
    // Stack: [0x01, 0x02, 0x03, 0x04, 0x01] - first item duplicated
}
```

## Gas Cost

**Cost:** 3 gas (GasFastestStep)

All DUP1-16 operations cost the same despite different stack depths accessed.

**Comparison:**

| Operation | Gas | Note               |
| --------- | --- | ------------------ |
| DUP4      | 3   | Duplicate 4th item |
| PUSH1-32  | 3   | Same cost tier     |
| POP       | 2   | Cheaper            |

## Common Usage

### Deep Stack Access

````solidity theme={null}
function complex() public pure {
    assembly {
        // Build deep stack
        let v1 := 1
        let v2 := 2
        let v3 := 3
        let v4 := 4

        // Access v1 from depth 4
        dup4
    }
}```

### Efficient Copies

```solidity
// Instead of multiple loads
assembly {
    let value := sload(slot)  // Expensive
    // Use value
    let value2 := sload(slot) // Wasteful!
}

// Use DUP to reuse
assembly {
    let value := sload(slot)  // Load once
    dup1                       // Copy
    // Use both copies
}
````

### Conditional Logic

```solidity theme={null}
assembly {
    let condition := calldataload(0)
    dup1  // Keep condition for later
    iszero
    jumpi(skip)
    // Use condition again
    skip:
}
```

## Stack Depth Requirements

### Minimum Depth

```solidity theme={null}
// DUP4 requires 4 items on stack
assembly {
    push1 0x01
    push1 0x02
    push1 0x03
    // Only 3 items - DUP4 will fail!
    dup4  // StackUnderflow
}
```

### Safe Usage

```solidity theme={null}
assembly {
    push1 0x01
    push1 0x02
    push1 0x03
    push1 0x04
    // Exactly 4 items - safe
    dup4  // Success
}
```

## Implementation

<Tabs>
  <Tab title="TypeScript">
    ```typescript theme={null}
    /**
     * DUP4 opcode (0x83) - Duplicate 4th stack item
     *
     * Stack: [..., value, ...] => [..., value, ..., value]
     * Gas: 3 (GasFastestStep)
     */
    export function handler_0x83_DUP4(frame: FrameType): EvmError | null {
      const gasErr = consumeGas(frame, FastestStep);
      if (gasErr) return gasErr;

      if (frame.stack.length < 4) {
        return { type: "StackUnderflow" };
      }

      const value = frame.stack[frame.stack.length - 4];
      const pushErr = pushStack(frame, value);
      if (pushErr) return pushErr;

      frame.pc += 1;
      return null;
    }
    ```
  </Tab>
</Tabs>

## Edge Cases

### Stack Underflow

```typescript theme={null}
// Insufficient stack depth
const frame = createFrame({
  stack: [100n, 100n, 100n]  // Only 3 items
});

const err = handler_0x83_DUP4(frame);
console.log(err); // { type: "StackUnderflow" }
```

### Stack Overflow

```typescript theme={null}
// Stack at maximum, can't add more
const frame = createFrame({
  stack: new Array(1024).fill(0n)
});

const err = handler_0x83_DUP4(frame);
console.log(err); // { type: "StackOverflow" }
```

### Out of Gas

```typescript theme={null}
// Insufficient gas
const frame = createFrame({
  stack: [100n, 100n, 100n, 100n],
  gasRemaining: 2n  // Need 3
});

const err = handler_0x83_DUP4(frame);
console.log(err); // { type: "OutOfGas" }
```

### Maximum Value

```typescript theme={null}
// Duplicate max uint256
const MAX = (1n << 256n) - 1n;
const frame = createFrame({
  stack: [0n, 0n, 0n, MAX]
});

handler_0x83_DUP4(frame);
console.log(frame.stack[frame.stack.length - 1]); // MAX (duplicated)
```

## References

* [Yellow Paper](https://ethereum.github.io/yellowpaper/paper.pdf) - Section 9.1 (Stack Operations)
* [EVM Codes - DUP4](https://www.evm.codes/#83?fork=cancun)
* [Solidity Assembly - dup4](https://docs.soliditylang.org/en/latest/yul.html#evm-opcodes)