pref: 换用卡马克的快速开方求倒函数

虽然用的地方不是很多()

app/gl_common.c

@@ -1,15 +1,36 @@
 #include "zf_common_headfile.h"
 #include "gl_headfile.h"
 
-
 int32_t limit(int32_t x, int32_t low, int32_t up)
 {
-    return x > up ? up : x < low ? low : x;
+    return x > up ? up : x < low ? low
+                                 : x;
+}
+int clip(int x, int low, int up)
+{
+    return x > up ? up : x < low ? low
+                                 : x;
 }
- int clip(int x, int low, int up) {
-     return x > up ? up : x < low ? low : x;
- }
 
-float fclip(float x, float low, float up) {
-     return x > up ? up : x < low ? low : x;
- }
+float fclip(float x, float low, float up)
+{
+    return x > up ? up : x < low ? low
+                                 : x;
+}
+
+float Q_sqrt(float number)
+{
+    long i;
+    float x2, y;
+    const float threehalfs = 1.5F;
+
+    x2 = number * 0.5F;
+    y  = number;
+    i  = *(long *)&y;           // evil floating point bit level hacking
+    i  = 0x5f3759df - (i >> 1); // what the fuck?
+    y  = *(float *)&i;
+    y  = y * (threehalfs - (x2 * y * y)); // 1st iteration
+    y  = y * (threehalfs - (x2 * y * y)); // 2nd iteration, this can be removed
+
+    return (1.0 / y);
+}