README.md

IntExpr

IntExpr is a Java library to evaluate int expressions. The expression has some similarities in the syntax to the C programming language.

Examples

The following code evaluates the string that represents an integer expression and prints the result:

package com.example;

import com.maroontress.intexpr.IntExpr;

public final class EvalDemo {
    public static void main(String[] args) {
        System.out.println(IntExpr.eval(args[0]));
    }
}

The output would be as follows:

$ java com.example.EvalDemo '(1+2*3<<4)%5'
2

Internally, the specified expression is converted to the expression in Reverse Polish notation (RPN) before evaluation. The expressions in RPN do not contain parentheses. The following code prints the syntax tree representing the expression in RPN, which corresponds to the specified expression:

package com.example;

import com.maroontress.intexpr.IntExpr;

public final class TreeDemo {
    public static void main(String[] args) {
        System.out.println(IntExpr.toTree(args[0]));
    }
}

The output would be as follows:

$ java com.example.TreeDemo '(1+2*3<<4)%5'
MOD
 ├ SHL
 │  ├ ADD
 │  │  ├ CONST 1
 │  │  └ MUL
 │  │     ├ CONST 2
 │  │     └ CONST 3
 │  └ CONST 4
 └ CONST 5

The opcodes that the tree includes (such as ADD, MUL, CONST, etc.) are defined in enum Opcode.

Numbers

Numbers are 32-bit signed integers in two's-complement notation (like values of int type in Java and C#, int32_t type in C23, and so on). They can represent integers from −2147483648 to 2147483647.

Expressions

A simple expression is just an integer constant.

Note that the minimum integer (−2147483648) cannot be constant because the expression -2147483648 is a unary - operator followed by 2147483648, and the integer is greater than the maximum integer (2147483647). So, you have to represent the minimum integer with (-2147483647 - 1).

In the following descriptions of legal expressions, expr refers to a complete expression:

• ( expr ): The parentheses alter the standard precedence to force the evaluation of the expression to precede the operation outside of them.
• unary + expr: The result is the expression itself (that is, no operation).
• unary - expr: The result is the negation of the expression.
• unary ! expr: The result is 1 if expr is 0, otherwise 0.
• unary ~ expr: The result is the logical negation on each bit, forming the ones' complement of the given binary value.
• expr * expr: The result is the product of the two expressions.
• expr / expr: The result is the quotient of the two expressions.
• expr % expr: The result is the remainder of the two expressions.
• expr + expr: The result is the sum of the two expressions.
• expr - expr: The result is the difference between the two expressions.
• expr1 << expr2: The result is the left arithmetic shift of expr1 by expr2.
• expr >> expr: The result is the right arithmetic shift of expr1 by expr2.
• expr1 < expr2: The result is 1 if expr1 is strictly less than expr2, otherwise 0.
• expr1 <= expr2: The result is 1 if expr1 is less than or equal to expr2, otherwise 0.
• expr1 > expr2: The result is 1 if expr1 is strictly greater than expr2, otherwise 0.
• expr1 >= expr2: The result is 1 if expr1 is greater than or equal to expr2, otherwise 0.
• expr1 == expr2: The result is 1 if expr1 is equal to expr2, otherwise 0.
• expr1 != expr2: The result is 1 if expr1 is not equal to expr2, otherwise 0.
• expr && expr: The result is 1 if both expressions are non-zero, otherwise 0.
• expr || expr: The result is 1 if either expression is non-zero, otherwise 0.

The operator precedence is as follows:

Precedence	Operator	Associativity
highest	unary + - ! ~
	* / %	Left-to-right
	+ -	Left-to-right
	<< >>	Left-to-right
	< <= > >=	Left-to-right
	== !=	Left-to-right
	&	Left-to-right
	^	Left-to-right
	|	Left-to-right
	&&	Left-to-right
lowest	||	Left-to-right

Errors

Syntax errors (such as a mismatched or missing parenthesis, a stray token, an unknown token) throw an IllegalArgumentException. The division by zero and the overflow during the evaluation throw an ArithmeticException.

API Reference

• com.maroontress.intexpr module