add FiniteField

.gitignore

@@ -0,0 +1 @@
+/target

.vscode/launch.json

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+{
+    // IntelliSense を使用して利用可能な属性を学べます。
+    // 既存の属性の説明をホバーして表示します。
+    // 詳細情報は次を確認してください: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "type": "lldb",
+            "request": "launch",
+            "name": "Debug executable 'encrypt'",
+            "cargo": {
+                "args": [
+                    "build",
+                    "--bin=encrypt",
+                    "--package=encrypt"
+                ],
+                "filter": {
+                    "name": "encrypt",
+                    "kind": "bin"
+                }
+            },
+            "args": [],
+            "cwd": "${workspaceFolder}"
+        },
+        {
+            "type": "lldb",
+            "request": "launch",
+            "name": "Debug unit tests in executable 'encrypt'",
+            "cargo": {
+                "args": [
+                    "test",
+                    "--no-run",
+                    "--bin=encrypt",
+                    "--package=encrypt"
+                ],
+                "filter": {
+                    "name": "encrypt",
+                    "kind": "bin"
+                }
+            },
+            "args": [],
+            "cwd": "${workspaceFolder}"
+        }
+    ]
+}

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "autocfg"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d468802bab17cbc0cc575e9b053f41e72aa36bfa6b7f55e3529ffa43161b97fa"
+
+[[package]]
+name = "bigdecimal"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6aaf33151a6429fe9211d1b276eafdf70cdff28b071e76c0b0e1503221ea3744"
+dependencies = [
+ "num-bigint",
+ "num-integer",
+ "num-traits",
+]
+
+[[package]]
+name = "encrypt"
+version = "0.1.0"
+dependencies = [
+ "bigdecimal",
+]
+
+[[package]]
+name = "num-bigint"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f93ab6289c7b344a8a9f60f88d80aa20032336fe78da341afc91c8a2341fc75f"
+dependencies = [
+ "autocfg",
+ "num-integer",
+ "num-traits",
+]
+
+[[package]]
+name = "num-integer"
+version = "0.1.44"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d2cc698a63b549a70bc047073d2949cce27cd1c7b0a4a862d08a8031bc2801db"
+dependencies = [
+ "autocfg",
+ "num-traits",
+]
+
+[[package]]
+name = "num-traits"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9a64b1ec5cda2586e284722486d802acf1f7dbdc623e2bfc57e65ca1cd099290"
+dependencies = [
+ "autocfg",
+]

Cargo.toml

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+[package]
+name = "encrypt"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bigdecimal = "0.3.0"

src/finite_field.rs

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+use std::{ops::Add, fmt::{self, Display}};
+
+use bigdecimal::{BigDecimal, Zero};
+
+#[derive(Debug, Clone)]
+pub struct FiniteFieldElement {
+    pub value: BigDecimal,
+    p: BigDecimal
+}
+
+fn pmod(x: BigDecimal, y: BigDecimal) -> BigDecimal {
+    if x < BigDecimal::zero() {
+        (y.clone() - (-x % y.clone())) % y
+    } else {
+        x % y
+    }
+}
+
+impl FiniteFieldElement {
+    pub fn new(value: BigDecimal, p: BigDecimal) -> Self {
+        Self { value: pmod(value, p.clone()), p }
+    }
+}
+
+impl Display for FiniteFieldElement {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{} mod {}", self.value, self.p)
+    }
+}
+
+impl Add for FiniteFieldElement {
+    type Output = Self;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        if self.p != rhs.p {
+            panic!("p doesn't match: {} != {}", self.p, rhs.p);
+        }
+        Self::new(self.value + rhs.value, self.p)
+    }
+}

src/lib.rs

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+pub mod finite_field;

src/main.rs

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+use bigdecimal::{BigDecimal, FromPrimitive};
+use encrypt::finite_field::FiniteFieldElement;
+
+macro_rules! b {
+    ( $x: expr ) => {
+        BigDecimal::from_i64($x).unwrap()
+    };
+}
+
+macro_rules! ffe {
+    ( $value: expr, $p: expr ) => {
+        FiniteFieldElement::new(b!($value), b!($p))
+    };
+}
+
+fn main() {
+    let a = ffe!(4, 5);
+    let b = ffe!(3, 5);
+    println!("{}", a + b);
+}