From aad186d67a497afde96813e3552434223548c4aa Mon Sep 17 00:00:00 2001
From: sf <dynm@outlook.com>
Date: Tue, 17 Dec 2024 19:50:30 +0800
Subject: [PATCH] feat(finite-field): add babybear

---
 src/finite-field/babybear.py | 176 +++++++++++++++++++++++++++++++++++
 1 file changed, 176 insertions(+)
 create mode 100644 src/finite-field/babybear.py

diff --git a/src/finite-field/babybear.py b/src/finite-field/babybear.py
new file mode 100644
index 0000000..f0fd360
--- /dev/null
+++ b/src/finite-field/babybear.py
@@ -0,0 +1,176 @@
+import random
+from typing import List
+
+class BabyBear:
+    P = 15 * (1 << 27) + 1
+    def __init__(self, value: int):
+        self.value = value % self.P
+
+    @classmethod
+    def zero(cls):
+        return cls(0)
+
+    @classmethod
+    def one(cls):
+        return cls(1)
+
+    @classmethod
+    def random(cls):
+        return cls(random.randint(0, cls.P - 1))
+
+    def __repr__(self):
+        return f"BabyBear({self.value})"
+
+    def __eq__(self, other):
+        if isinstance(other, BabyBear):
+            return self.value == other.value
+        return False
+
+    def __add__(self, other):
+        if isinstance(other, BabyBear):
+            return BabyBear(self.add(self.value, other.value))
+        raise TypeError("Unsupported operand type for +")
+
+    def __sub__(self, other):
+        if isinstance(other, BabyBear):
+            return BabyBear(self.sub(self.value, other.value))
+        raise TypeError("Unsupported operand type for -")
+
+    def __mul__(self, other):
+        if isinstance(other, BabyBear):
+            return BabyBear(self.mul(self.value, other.value))
+        raise TypeError("Unsupported operand type for *")
+
+    def __neg__(self):
+        return BabyBear(self.P - self.value)
+
+    def inv(self):
+        return self.pow(self.P - 2)
+
+    def pow(self, n: int):
+        result = BabyBear.one()
+        base = self
+        while n > 0:
+            if n & 1:
+                result *= base
+            base *= base
+            n >>= 1
+        return result
+
+    @classmethod
+    def add(cls, lhs: int, rhs: int) -> int:
+        x = (lhs + rhs) % cls.P
+        return x
+
+    @classmethod
+    def sub(cls, lhs: int, rhs: int) -> int:
+        x = (lhs - rhs) % cls.P
+        return x
+
+    @classmethod
+    def mul(cls, lhs: int, rhs: int) -> int:
+        return (lhs * rhs) % cls.P
+
+class BabyBearExtElem:
+    BETA = BabyBear(11)
+    NBETA = BabyBear(BabyBear.P - 11)
+
+    def __init__(self, elems: List[BabyBear]):
+        assert len(elems) == 4, "ExtElem must have 4 elements"
+        self.elems = elems
+
+    @classmethod
+    def zero(cls):
+        return cls([BabyBear.zero()] * 4)
+
+    @classmethod
+    def one(cls):
+        return cls([BabyBear.one()] + [BabyBear.zero()] * 3)
+
+    @classmethod
+    def random(cls):
+        return cls([BabyBear.random() for _ in range(4)])
+
+    def __repr__(self):
+        return f"BabyBearExtElem({self.elems})"
+
+    def __eq__(self, other):
+        if isinstance(other, BabyBearExtElem):
+            return self.elems == other.elems
+        return False
+
+    def __add__(self, other):
+        if isinstance(other, BabyBearExtElem):
+            return BabyBearExtElem([a + b for a, b in zip(self.elems, other.elems)])
+        raise TypeError("Unsupported operand type for +")
+
+    def __sub__(self, other):
+        if isinstance(other, BabyBearExtElem):
+            return BabyBearExtElem([a - b for a, b in zip(self.elems, other.elems)])
+        raise TypeError("Unsupported operand type for -")
+
+    def __mul__(self, other):
+        if isinstance(other, BabyBearExtElem):
+            a, b = self.elems, other.elems
+            return BabyBearExtElem([
+                a[0] * b[0] + self.NBETA * (a[1] * b[3] + a[2] * b[2] + a[3] * b[1]),
+                a[0] * b[1] + a[1] * b[0] + self.NBETA * (a[2] * b[3] + a[3] * b[2]),
+                a[0] * b[2] + a[1] * b[1] + a[2] * b[0] + self.NBETA * (a[3] * b[3]),
+                a[0] * b[3] + a[1] * b[2] + a[2] * b[1] + a[3] * b[0]
+            ])
+        elif isinstance(other, BabyBear):
+            return BabyBearExtElem([elem * other for elem in self.elems])
+        raise TypeError("Unsupported operand type for *")
+
+    def __neg__(self):
+        return BabyBearExtElem([-elem for elem in self.elems])
+
+    def inv(self):
+        a = self.elems
+        b0 = a[0] * a[0] + self.BETA * (a[1] * (a[3] + a[3]) - a[2] * a[2])
+        b2 = a[0] * (a[2] + a[2]) - a[1] * a[1] + self.BETA * (a[3] * a[3])
+        c = b0 * b0 + self.BETA * b2 * b2
+        c_inv = c.inv()
+        b0, b2 = b0 * c_inv, b2 * c_inv
+        return BabyBearExtElem([
+            a[0] * b0 + self.BETA * a[2] * b2,
+            -a[1] * b0 + self.NBETA * a[3] * b2,
+            -a[0] * b2 + a[2] * b0,
+            a[1] * b2 - a[3] * b0
+        ])
+
+    def pow(self, n: int):
+        result = BabyBearExtElem.one()
+        base = self
+        while n > 0:
+            if n & 1:
+                result *= base
+            base *= base
+            n >>= 1
+        return result
+
+# Example usage:
+if __name__ == "__main__":
+    a = BabyBear(5)
+    b = BabyBear(7)
+    print(f"a = {a}")
+    print(f"b = {b}")
+    print(f"a + b = {a + b}")
+    print(f"a - b = {a - b}")
+    print(f"a * b = {a * b}")
+    print(f"a.inv() = {a.inv()}")
+    print(f"a.pow(3) = {a.pow(3)}")
+    # a.inv*a
+    print(f"a.inv() * a = {a.inv() * a}")  # Should be 1
+
+    x = BabyBearExtElem.random()
+    y = BabyBearExtElem.random()
+    print(f"x = {x}")
+    print(f"y = {y}")
+    print(f"x + y = {x + y}")
+    print(f"x - y = {x - y}")
+    print(f"x * y = {x * y}")
+    print(f"x.inv() = {x.inv()}")
+    print(f"x.pow(3) = {x.pow(3)}")
+    print(f"x * x.inv() = {x * x.inv()}")  # Should be 1
+    print(f"x_neg = {-x}, x + x_neg = {x+(-x)}")