https://github.com/maroontress/intexpr.java
A library to evaluate integer expressions in Java.
https://github.com/maroontress/intexpr.java
calculator eval int32 reverse-polish-notation
Last synced: 3 months ago
JSON representation
A library to evaluate integer expressions in Java.
- Host: GitHub
- URL: https://github.com/maroontress/intexpr.java
- Owner: maroontress
- License: other
- Created: 2022-01-27T11:42:57.000Z (over 3 years ago)
- Default Branch: main
- Last Pushed: 2022-01-29T17:38:51.000Z (over 3 years ago)
- Last Synced: 2025-01-21T21:32:02.520Z (5 months ago)
- Topics: calculator, eval, int32, reverse-polish-notation
- Language: Java
- Homepage: https://maroontress.github.io/IntExpr-Java
- Size: 83 KB
- Stars: 1
- Watchers: 2
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# 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](src/test/java/com/example/EvalDemo.java) evaluates the
string that represents an integer expression and prints the result:
```java
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:
```plaintext
$ java com.example.EvalDemo '(1+2*3<<4)%5'
2
```
Internally, the specified expression is converted to the expression in
[_Reverse Polish notation_][wikipedia-rpn] (RPN) before evaluation. The
expressions in RPN do not contain parentheses.
[The following code](src/test/java/com/example/TreeDemo.java) prints the syntax
tree representing the expression in RPN, which corresponds to the specified
expression:
```java
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:
```plaintext
$ 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`](src/main/java/com/maroontress/intexpr/impl/Opcode.java).
## 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][apiref-maroontress.intexpr] module
[wikipedia-rpn]: https://en.wikipedia.org/wiki/Reverse_Polish_notation
[apiref-maroontress.intexpr]:
https://maroontress.github.io/IntExpr-Java/api/latest/html/index.html