((x))is the same as
(x). Prefer only one layer of parentheses.
value=$(( ((offset + index)) * 512 ))
value=$(( (offset + index) * 512 ))
ShellCheck found doubly nested parentheses in an arithmetic expression. While the syntax for an arithmetic expansion is
$((..)), this does not imply that parentheses in the expression should also be doubled.
(((x))) are all identical, so you might as well use only one layer of parentheses.
This is a stylistic suggestion. If you prefer keeping both parentheses, you can ignore this message.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.