Fix SDL_TICKS_PASSED (#234) (#235)

SDL_TICKS_PASSED is meant to compare 32-bit tick counts in a way that
works correctly when the counter has recently wrapped around. The Python
implementation just did a straight integer comparison.

Author: benrg

sdl2/test/timer_test.py

@@ -71,3 +71,10 @@ def timerfunc(interval, param):
     assert len(calls) == orig_calls
     # Wait a bit, so the last executing handlers can finish
     sdl2.SDL_Delay(10)
+
+def test_SDL_TICKS_PASSED(with_sdl):
+    for A in (0, 9999, 0xFFFF0000, 0xFFFFFFFF):
+        assert sdl2.SDL_TICKS_PASSED(A, A)
+        for delta in (1, 100, 1000000, 0x7FFFFFFF):
+            assert sdl2.SDL_TICKS_PASSED(A, (A - delta) & 0xFFFFFFFF)
+            assert not sdl2.SDL_TICKS_PASSED(A, (A + delta) & 0xFFFFFFFF)

sdl2/timer.py

@@ -23,7 +23,7 @@
 # Macros & inline functions
 
 def SDL_TICKS_PASSED(A, B):
-    return (B - A) <= 0
+    return ((A - B) & 0xFFFFFFFF) <= 0x80000000
 
 
 # Raw ctypes function definitions