mmap (POSIX function)

`mmap` is a POSIX function used in operating systems to map files or devices into memory. Instead of reading from a file using traditional input/output functions, `mmap` allows a program to access file contents directly as if they were part of its own memory. This can speed up file processing and enable efficient handling of large files. It is commonly used in applications that require rapid access to data, like databases or multimedia processing, facilitating both reading and writing via memory operations rather than slower file system calls.