twn_util: separate internal c-only features from public header

src/rendering/twn_sprites.c

@@ -2,6 +2,7 @@
 #include "twn_rendering_c.h"
 #include "twn_engine_context_c.h"
 #include "twn_util.h"
+#include "twn_util_c.h"
 #include "twn_textures_c.h"
 
 #include <stb_ds.h>

src/twn_textures.c

@@ -1,6 +1,7 @@
 #include "twn_textures_c.h"
 #include "twn_config.h"
 #include "twn_util.h"
+#include "twn_util_c.h"
 #include "twn_engine_context_c.h"
 
 #include <SDL2/SDL.h>

src/twn_util_c.h

@@ -1,7 +1,37 @@
 #ifndef TWN_UTIL_C_H
 #define TWN_UTIL_C_H
 
+#include "twn_types.h"
+
 /* note: you must free the returned string */
 char *expand_asterisk(const char *mask, const char *to);
 
+/* http://www.azillionmonkeys.com/qed/sqroot.html */
+static inline float fast_sqrt(float x)
+{
+    union {
+        float f;
+        uint32_t u;
+    } pun = {.f = x};
+
+    pun.u += 127 << 23;
+    pun.u >>= 1;
+
+    return pun.f;
+}
+
+
+static inline Vec2 fast_cossine(float a) {
+    const float s = sinf(a);
+    return (Vec2){
+        .x = fast_sqrt(1.0f - s * s) * (a >= (float)M_PI_2 && a < (float)(M_PI + M_PI_2) ? -1 : 1),
+        .y = s
+    };
+}
+
+static inline bool is_power_of_two(int x)
+{
+    return (x != 0) && ((x & (x - 1)) == 0);
+}
+
 #endif