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Operator documentation
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## Language reference
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## Language reference
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* [Operators](lang/operators.md)
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* [Inline assembly syntax](lang/assembly.md)
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* [Inline assembly syntax](lang/assembly.md)
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* [Important guidelines regarding reentrancy](lang/reentrancy.md)
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* [Important guidelines regarding reentrancy](lang/reentrancy.md)
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# Operators
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Unlike in high-level languages, operators in Millfork have limited applicability.
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Not every well-formed expression is actually compilable.
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Further improvements to the compiler may increase the number of acceptable combinations.
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## Precedence
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Millfork has different operator precedence compared to most other languages. From highest to lowest it goes:
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* `*`, `*'`
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* `+`, `+'`, `-`, `-'`, `|`, `&`, `^`, `>>`, `>>'`, `<<`, `<<'`, `>>>>`
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* `:`
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* `==`, `!=`, `<`, `>`, `<=`, `>=`
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* `&&`
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* `||`
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* assignment and in-place modification operators
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You cannot use two different operators at the same precedence levels without using parentheses to disambiguate.
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It is to prevent confusion about whether `a + b & c << d` means `(a + b) & (c << d)` `((a + b) & c) << d` or something else.
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The only exceptions are `+` and `-`, and `+'` and `-'`.
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They are interpeted as expected: `5 - 3 + 2 == 4` and `5 -' 3 +' 2 == 4`.
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Note that you cannot mix `+'` and `-'` with `+` and `-`.
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## Argument types
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In the descriptions below, arguments to the operators are explained as follows:
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* `byte` means any one-byte type
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* `word` means any two-byte type, or a byte expanded to a word
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* `long` means any type longer than two bytes, or a shorted type expanded to such length to match the other argument
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* `constant` means a compile-time constant
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* `simple` means either: a constant, a non-stack variable,
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a pointer indexed with a constant, a pointer indexed with a non-stack variable,
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an array indexed with a constant, an array indexed with a non-stack variable,
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an array indexed with a sum of a constant and a non-stack variable,
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or a split-word expression made of two simple expressions.
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Examples: `1`, `a`, `p[2]`, `p[i]`, `arr[2]`, `arr[i]`, `arr[i+2]`, `h:l`, `h[i]:l[i]`
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Such expressions have the property that the only register they may clobber is Y.
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* `mutable` means an expression than can be assigned to
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## Binary arithmetic operators
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* `+`, `-`:
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`byte + byte`
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`word + word`
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`long + long`
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* `*`: 8-bit multiplication
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`byte * constant byte`
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`constant byte * byte`
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There are no division, remainder or modulo operators.
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## Bitwise operators
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* `|`, `^`, `&`: OR, EXOR and AND
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`byte | byte`
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* `<<`, `>>`: bit shifting; shifting right pads the result with zeroes
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`byte * constant byte`
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* `>>>>`: shifting a 9-bit value and returning a byte; `a >>>> b` is equivalent to `(a & $1FF) >> b`, but the latter doesn't compile yet
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`word >>>> constant byte`
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## Decimal arithmetic operators
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These operators work using the decimal arithmetic and will not work on Ricoh CPU's.
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* `+'`, `-'`: decimal addition/subtraction
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`byte +' byte`
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`word +' word`
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`long +' long`
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* `*'`: decimal multiplication
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`constant *' constant`
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* `<<'`, `>>'`: decimal multiplication/division by power of two
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`byte * constant byte`
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## Comparison operators
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These operators (except for `!=`) can accept more than 2 arguments.
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In such case, the result is true if each comparison in the group is true.
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Note you cannot mix those operators, so `a <= b < c` is not valid.
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* `==`: equality
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`byte == byte`
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`word == word`
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`long == long`
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* `!=`: inequality
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`byte == byte`
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`word == word`
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`long == long`
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* `>`, `<`, `<=`, `>=`: inequality
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`byte > byte`
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`word > word`
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`long > long`
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Currently, `>`, `<`, `<=`, `>=` operators perform unsigned comparison
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if none of the types of their arguments is signed,
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and fail to compile otherwise. This will be changed in the future.
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## Assignment operators
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* `=`: normal assignment
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`mutable byte = byte`
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`mutable word = word`
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`mutable long = long`
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* `+=`, `+'=`, `|=`, `^=`, `&=`: modification in place
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`mutable byte += byte`
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`mutable word += word`
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`mutable long += long`
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* `<<=`, `>>=`, `<<'=`, `>>'=`: shift in place
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`mutable byte <<= constant byte`
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`mutable word <<= constant byte`
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`mutable long <<= constant byte`
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* `-=`, `-'=`: subtraction in place
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`mutable byte -= byte`
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`mutable word -= simple word`
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`mutable long -= simple long`
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* `*=`: multiplication in place
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`mutable byte *= constant byte`
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There are no `*'=` operator yet.
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