tests/extmod/ticks_diff: Test for new semantics of ticks_diff().

tests/extmod/ticks_diff.py

@@ -0,0 +1,33 @@
+from utime import ticks_diff, ticks_add
+
+MAX = ticks_add(0, -1)
+# Should be done like this to avoid small int overflow
+MODULO_HALF = MAX // 2 + 1
+
+# Invariants:
+# if ticks_diff(a, b) = c,
+# then ticks_diff(b, a) = -c
+
+assert ticks_diff(1, 0) == 1, ticks_diff(1, 0)
+assert ticks_diff(0, 1) == -1
+
+assert ticks_diff(0, MAX) == 1
+assert ticks_diff(MAX, 0) == -1
+
+assert ticks_diff(0, MAX - 1) == 2
+
+# Maximum "positive" distance
+assert ticks_diff(MODULO_HALF, 1) == MODULO_HALF - 1, ticks_diff(MODULO_HALF, 1)
+# Step further, and it becomes a negative distance
+assert ticks_diff(MODULO_HALF, 0) == -MODULO_HALF
+
+# Offsetting that in either direction doesn't affect the result
+off = 100
+# Cheating and skipping to use ticks_add() when we know there's no wraparound
+# Real apps should use always it.
+assert ticks_diff(MODULO_HALF + off, 1 + off) == MODULO_HALF - 1
+assert ticks_diff(MODULO_HALF + off, 0 + off) == -MODULO_HALF
+assert ticks_diff(MODULO_HALF - off, ticks_add(1, -off)) == MODULO_HALF - 1
+assert ticks_diff(MODULO_HALF - off, ticks_add(0, -off)) == -MODULO_HALF
+
+print("OK")

tests/extmod/ticks_diff.py.exp

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+OK