py: Fix build error when float disabled; add test for divmod.

tests/float/float_divmod.py

@@ -0,0 +1,25 @@
+# test floating point floor divide and modulus
+# it has some tricky corner cases
+
+def test(x, y):
+    div, mod = divmod(x, y)
+    print('%.8f %.8f %.8f %.8f' % (x // y, x % y, div, mod))
+    print(div == x // y, mod == x % y, abs(div * y + mod - x) < 1e-15)
+
+test(1.23456, 0.7)
+test(-1.23456, 0.7)
+test(1.23456, -0.7)
+test(-1.23456, -0.7)
+
+a = 1.23456
+b = 0.7
+test(a, b)
+test(a, -b)
+test(-a, b)
+test(-a, -b)
+
+for i in range(25):
+    x = (i - 12.5) / 6
+    for j in range(25):
+        y = (j - 12.5) / 6
+        test(x, y)