diff --git a/chapter3_function_approximation_and_fft/rational_function_approximation.py b/chapter3_function_approximation_and_fft/rational_function_approximation.py
new file mode 100644
index 0000000..e9c7da7
--- /dev/null
+++ b/chapter3_function_approximation_and_fft/rational_function_approximation.py
@@ -0,0 +1,49 @@
+# !/usr/bin/env python
+# -*- coding: utf-8 -*-
+"""
+@Time        : 2021/1/2 18:48
+@Author      : Albert Darren
+@Contact     : 2563491540@qq.com
+@File        : rational_function_approximation.py
+@Version     : Version 1.0.0
+@Description : TODO 自己实现有理逼近，帕德逼近,Stein算法
+@Created By  : PyCharm
+"""
+
+
+def gcd_core(a: int, b: int):
+    if a == 0:
+        return b
+    if b == 0:
+        return a
+    while a & 0x1 == 0:
+        a >>= 1
+    if a < b:
+        b = (b - a) >> 1
+        return gcd_core(b, a)
+    else:
+        a = (a - b) >> 1
+        return gcd_core(a, b)
+
+
+def gcd(a: int, b: int):
+    """
+    stein算法实现求a,b整数的最大公约数
+    :param a: 整数a
+    :param b: 整数b
+    :return: 最大公约数
+    """
+    c = 0
+    while a & 0x1 == 0 and b & 0x1 == 0:
+        a >>= 1
+        b >>= 1
+        c += 1
+    if a & 0x1 == 0:
+        a >>= 1
+        return gcd_core(a, b) << c
+    else:
+        return gcd_core(b, a) << c
+
+
+if __name__ == '__main__':
+    print(gcd(1024,64))