Function pattern_data_offset 

pub fn pattern_data_offset(header: &XmHeader) -> usize

Absolute byte offset in the source blob where pattern data begins, i.e. just past the file header + order table.

The spec’s header_size dword at offset 60 is measured from offset 60 itself (inclusive of the size dword) — so the block spans [60 .. 60 + header_size). For a canonical file with header_size == 0x114, this lands at offset 0x150 = 336, exactly at the end of the 256-byte order table that starts at offset 80.