stdlib: added SDL_utf8strlen().

include/SDL_stdinc.h

@@ -416,6 +416,7 @@ extern DECLSPEC char *SDLCALL SDL_strlwr(char *str);
 extern DECLSPEC char *SDLCALL SDL_strchr(const char *str, int c);
 extern DECLSPEC char *SDLCALL SDL_strrchr(const char *str, int c);
 extern DECLSPEC char *SDLCALL SDL_strstr(const char *haystack, const char *needle);
+extern DECLSPEC size_t SDLCALL SDL_utf8strlen(const char *str);
 
 extern DECLSPEC char *SDLCALL SDL_itoa(int value, char *str, int radix);
 extern DECLSPEC char *SDLCALL SDL_uitoa(unsigned int value, char *str, int radix);

src/dynapi/SDL_dynapi_overrides.h

@@ -624,3 +624,4 @@
 #define SDL_MemoryBarrierReleaseFunction SDL_MemoryBarrierReleaseFunction_REAL
 #define SDL_MemoryBarrierAcquireFunction SDL_MemoryBarrierAcquireFunction_REAL
 #define SDL_JoystickGetDeviceInstanceID SDL_JoystickGetDeviceInstanceID_REAL
+#define SDL_utf8strlen SDL_utf8strlen_REAL

src/dynapi/SDL_dynapi_procs.h

@@ -656,3 +656,4 @@ SDL_DYNAPI_PROC(SDL_JoystickType,SDL_JoystickGetType,(SDL_Joystick *a),(a),retur
 SDL_DYNAPI_PROC(void,SDL_MemoryBarrierReleaseFunction,(void),(),)
 SDL_DYNAPI_PROC(void,SDL_MemoryBarrierAcquireFunction,(void),(),)
 SDL_DYNAPI_PROC(SDL_JoystickID,SDL_JoystickGetDeviceInstanceID,(int a),(a),return)
+SDL_DYNAPI_PROC(size_t,SDL_utf8strlen,(const char *a),(a),return)

src/stdlib/SDL_string.c

@@ -509,6 +509,23 @@ size_t SDL_utf8strlcpy(SDL_OUT_Z_CAP(dst_bytes) char *dst, const char *src, size
     return bytes;
 }
 
+size_t
+SDL_utf8strlen(const char *str)
+{
+    size_t retval = 0;
+    const char *p = str;
+    char ch;
+
+    while ((ch = *(p++))) {
+        /* if top two bits are 1 and 0, it's a continuation byte. */
+        if ((ch & 0xc0) != 0x80) {
+            retval++;
+        }
+    }
+
+    return retval;
+}
+
 size_t
 SDL_strlcat(SDL_INOUT_Z_CAP(maxlen) char *dst, const char *src, size_t maxlen)
 {