なるほど、本当にここに書いてあるという主張してるのか

2.6.4 Arithmetic Expansion
Arithmetic expansion provides a mechanism for evaluating an arithmetic expression and substituting its value. The format for arithmetic expansion shall be as follows:

$((expression))

The expression shall be treated as if it were in double-quotes, except that a double-quote inside the expression is not treated specially. The shell shall expand all tokens in the expression for parameter expansion, command substitution, and quote removal.

Next, the shell shall treat this as an arithmetic expression and substitute the value of the expression. The arithmetic expression shall be processed according to the rules given in Arithmetic Precision and Operations, with the following exceptions:

Only signed long integer arithmetic is required.

Only the decimal-constant, octal-constant, and hexadecimal-constant constants specified in the ISO C standard, Section 6.4.4.1 are required to be recognized as constants.

The sizeof() operator and the prefix and postfix "++" and "--" operators are not required.

Selection, iteration, and jump statements are not supported.