Problem

In low-level systems code such as firmware used by Meta hardware platforms, copying bytes within the same buffer must be safe even when the source and destination ranges overlap. Implement a function that performs memmove-style copying on a byte array.

Given a list of integers buffer representing bytes, and integers dst, src, and count, copy count bytes starting at index src to index dst in place. Return the modified buffer.

Unlike a naive forward copy, your implementation must work correctly when the source and destination ranges overlap.

Formal Specification

• Input: buffer: List[int], dst: int, src: int, count: int
• Output: The same buffer after copying count bytes from src to dst
• Each value in buffer is in the range 0..255

Examples

Example 1

• Input: buffer = [1, 2, 3, 4, 5, 6], dst = 2, src = 0, count = 4
• Output: [1, 2, 1, 2, 3, 4]
• Explanation: The ranges overlap, so copying must preserve the original source bytes.

Example 2

• Input: buffer = [10, 20, 30, 40, 50], dst = 0, src = 2, count = 3
• Output: [30, 40, 50, 40, 50]
• Explanation: The source starts after the destination, so a forward copy is safe.

Constraints

• 0 <= len(buffer) <= 10^5
• 0 <= count <= len(buffer)
• 0 <= src, dst <= len(buffer)
• src + count <= len(buffer)
• dst + count <= len(buffer)