From d73e4337bf56b89cd00b5f866a35c8ad3fb4115c Mon Sep 17 00:00:00 2001
From: Sam Hocevar <sam@hocevar.net>
Date: Fri, 10 Mar 2006 09:31:32 +0000
Subject: [PATCH]   * Implemented a few math functions in our kernel: cos(),
 sin(), sqrt().

---
 kernel/kernel.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/kernel.h |  6 +++++
 2 files changed, 64 insertions(+)

diff --git a/kernel/kernel.c b/kernel/kernel.c
index 091e4ff..172ca26 100644
--- a/kernel/kernel.c
+++ b/kernel/kernel.c
@@ -211,4 +211,62 @@ int gettimeofday(struct timeval *tv, struct timezone *tz)
     return 0;
 }
 
+/* math.h functions */
+double cos(double x)
+{
+    double ret = 0.0;
+    double x2;
+    double num = 1.0;
+    double fact = 1.0;
+    int i;
+
+    x = x - ((double)(int)(x / (2 * M_PI))) * (2 * M_PI);
+    x2 = x * x;
+
+    /* cos(x) = 1/0! - x^2/2! + x^4/4! - x^6/6! ... */
+    for(i = 0; i < 10; i++)
+    {
+        ret += num / fact;
+        num *= - x2;
+        fact *= (2 * i + 1) * (2 * i + 2);
+    }
+
+    return ret;
+}
+
+double sin(double x)
+{
+    double ret = 0.0;
+    double x2;
+    double num;
+    double fact = 1.0;
+    int i;
+
+    x = x - ((double)(int)(x / (2 * M_PI))) * (2 * M_PI);
+    x2 = x * x;
+    num = x;
+
+    /* sin(x) = x/1! - x^3/3! + x^5/5! - x^7/7! ... */
+    for(i = 0; i < 10; i++)
+    {
+        ret += num / fact;
+        num *= - x2;
+        fact *= (2 * i + 2) * (2 * i + 3);
+    }
+
+    return ret;
+}
+
+double sqrt(double x)
+{
+    double ret = x;
+    int i;
+
+    /* This is Newton's method */
+    for(i = 0; i < 10; i++)
+        ret = (ret * ret + x) / (ret * 2.0);
+
+    return ret;
+}
+
 #endif /* __KERNEL__ */
diff --git a/kernel/kernel.h b/kernel/kernel.h
index 7424e18..45f3e47 100644
--- a/kernel/kernel.h
+++ b/kernel/kernel.h
@@ -24,6 +24,7 @@
 #define BUFSIZ 4096
 #define RAND_MAX ((unsigned int)0x8000000)
 #define INT_MAX ((int)0x7fffffff)
+#define M_PI 3.14159265358979323846
 #define __BYTE_ORDER 1
 #define __BIG_ENDIAN 2
 
@@ -110,3 +111,8 @@ void usleep(unsigned long usec);
 /* time.h functions */
 int gettimeofday(struct timeval *tv, struct timezone *tz);
 
+/* math.h functions */
+double cos(double x);
+double sin(double x);
+double sqrt(double x);
+