From 686499db7ac1e0520b6f43684ec7b0449a505b2c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=B8=B8=E7=94=B1?= <huang_xianjun@live.cn>
Date: Thu, 11 Nov 2021 14:52:39 +0800
Subject: [PATCH] =?UTF-8?q?69.Sqrt(x)=20c=E8=AF=AD=E8=A8=80=E5=AE=9E?=
 =?UTF-8?q?=E7=8E=B0=E6=9B=B4=E6=94=B9?=
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---
 c/main.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/c/main.c b/c/main.c
index bd1b4ed..0392422 100644
--- a/c/main.c
+++ b/c/main.c
@@ -3,6 +3,11 @@
 //
 #include <stdio.h>
 
+/**
+ * 69.Sqrt(x)
+ * @param x x
+ * @return 平方根
+ */
 int mySqrt(int x) {
     union {
         long long i;
@@ -10,23 +15,28 @@ int mySqrt(int x) {
     }u;
     double xHalf = 0.5 * x;
     u.f = x;
-    u.i = 0x5FE6EC85E7DE30DALL - (u.i >> 1);
-    u.f = u.f * (1.5 - xHalf * u.f * u.f);
-    u.f = u.f * (1.5 - xHalf * u.f * u.f);
-    u.f = u.f * (1.5 - xHalf * u.f * u.f);
-    return 1.0 / u.f;
+    u.i = 0x1FF7A3BEA91D9B1B + (u.i >> 1);
+    u.f = u.f * 0.5 + xHalf / u.f;
+    u.f = u.f * 0.5 + xHalf / u.f;
+    u.f = u.f * 0.5 + xHalf / u.f;
+    return u.f;
 }
 
+/**
+ * 69.Sqrt(x)
+ * @param x x
+ * @return 平方根
+ */
 int mySqrt1(int x) {
     double xHalf = 0.5 * x;
     double f = x;
     long long i = *(long long *) &f;
-    i = 0x5FE6EC85E7DE30DALL - (i >> 1);
+    i = 0x1FF7A3BEA91D9B1B + (i >> 1);
     f = *(double *) &i;
-    f = f * (1.5 - xHalf * f * f); // 牛顿迭代法，重复此句可提高精度
-    f = f * (1.5 - xHalf * f * f);
-    f = f * (1.5 - xHalf * f * f); // 三次迭代
-    return 1.0 / f;
+    f = f * 0.5 + xHalf / f; // 牛顿迭代法，重复此句可提高精度
+    f = f * 0.5 + xHalf / f;
+    f = f * 0.5 + xHalf / f; // 三次迭代
+    return f;
 }
 
 int main() {