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Arithmetic Evaluation

An ability to perform integer arithmetic is provided with the builtin let. Evaluations are performed using long arithmetic. A leading 0x or 0X denotes hexadecimal. Otherwise, numbers are of the form [base#]n where base is a decimal number between two and thirty-six representing the arithmetic base and n is a number in that base (for example, 16#ff is 255 in hexadecimal). If base is omitted then base 10 is used. For backwards compatibility the form [16]ff is also accepted.

An arithmetic expression uses nearly the same syntax, precedence, and associativity of expressions in C. The following operators are supported (listed in decreasing order of precedence):

+ - ! ~ ++ --
Unary plus/minus, logical NOT, complement, {pre,post}{in,de}crement
<< >>
Bitwise shift left, right.
Bitwise AND
Bitwise XOR
Bitwise OR
* / %
Multiplication, division, modulus (remainder)
+ -
Addition, subtraction
< > <= >=
== !=
Equality and inequality
Logical AND
|| ^^
Logical OR, XOR
? :
Ternary operator
= += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
Comma operator

The operators &&, ||, &&=, and ||= are short-circuiting, and only one of the latter two expressions in a ternary operator is evaluated. Note the precedence of the bitwise AND, OR, and XOR operators.

An expression of the form #\x where x is any character gives the ASCII value of this character. An expression of the form #foo gives the ASCII value of the first character of the value of the parameter foo.

Named parameters and subscripted arrays can be referenced by name within an arithmetic expression without using the parameter substitution syntax.

An internal integer representation of a named parameter can be specified with the integer builtin. Arithmetic evaluation is performed on the value of each assignment to a named parameter declared integer in this manner.

Since many of the arithmetic operators require quoting, an alternative form of the let command is provided. For any command which begins with a ((, all the characters until a matching )) are treated as a quoted expression. More precisely, (( ... )) is equivalent to let "...".

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