math.easing: fix in_out_back/1, add tests (#25939)

Author: tankf33der

vlib/math/easing/easing.v

@@ -192,7 +192,7 @@ pub fn out_back(x f64) f64 {
 @[inline]
 pub fn in_out_back(x f64) f64 {
 	return if x < 0.5 {
-		(pow(2.0 * x, x) * ((c2 + 1) * 2.0 * x - c2)) / 2.0
+		(pow(2.0 * x, 2.0) * ((c2 + 1) * 2.0 * x - c2)) / 2.0
 	} else {
 		(pow(2.0 * x - 2.0, 2.0) * ((c2 + 1.0) * (x * 2.0 - 2.0) + c2) + 2.0) / 2.0
 	}

vlib/math/easing/easing_test.v

@@ -9,3 +9,8 @@ fn test_linear() {
 		assert easing.linear(x) == x
 	}
 }
+
+fn test_in_out_back() {
+	assert easing.in_out_back(0.333).eq_epsilon(-0.04451079425639395)
+	assert easing.in_out_back(3).eq_epsilon(136.79638)
+}

vlib/v/slow_tests/inout/math_easing_tables.out

@@ -54,16 +54,16 @@
 +------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 |  x   |  linear |   sine  |   quad  |   cubic |   quart |   quint |   expo  |    circ |   back  | elastic |  bounce |
 +------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
-| -0.5 |  -0.500 |   0.500 |   0.500 |  -0.500 |   0.500 |  -0.500 |   0.000 |   0.500 |     nan |  -0.000 |  -7.355 |
-| -0.4 |  -0.400 |   0.345 |   0.320 |  -0.256 |   0.205 |  -0.164 |   0.000 |   0.200 |     nan |   0.000 |  -5.925 |
-| -0.3 |  -0.300 |   0.206 |   0.180 |  -0.108 |   0.065 |  -0.039 |   0.000 |   0.100 |     nan |  -0.000 |  -4.797 |
-| -0.2 |  -0.200 |   0.095 |   0.080 |  -0.032 |   0.013 |  -0.005 |   0.000 |   0.042 |     nan |   0.000 |  -3.972 |
-| -0.1 |  -0.100 |   0.024 |   0.020 |  -0.004 |   0.001 |  -0.000 |   0.000 |   0.010 |     nan |  -0.000 |  -3.450 |
-| -0.0 |  -0.000 |  -0.000 |   0.000 |  -0.000 |   0.000 |  -0.000 |   0.000 |   0.000 |     nan |   0.000 |   0.000 |
-|  0.1 |   0.100 |   0.024 |   0.020 |   0.004 |   0.001 |   0.000 |   0.002 |   0.010 |  -0.799 |   0.000 |  -3.046 |
-|  0.2 |   0.200 |   0.095 |   0.080 |   0.032 |   0.013 |   0.005 |   0.008 |   0.042 |  -0.482 |  -0.004 |  -2.347 |
-|  0.3 |   0.300 |   0.206 |   0.180 |   0.108 |   0.065 |   0.039 |   0.031 |   0.100 |  -0.188 |   0.024 |  -2.416 |
-|  0.4 |   0.400 |   0.345 |   0.320 |   0.256 |   0.205 |   0.164 |   0.125 |   0.200 |   0.129 |  -0.117 |   0.349 |
+| -0.5 |  -0.500 |   0.500 |   0.500 |  -0.500 |   0.500 |  -0.500 |   0.000 |   0.500 |  -3.095 |  -0.000 |  -7.355 |
+| -0.4 |  -0.400 |   0.345 |   0.320 |  -0.256 |   0.205 |  -0.164 |   0.000 |   0.200 |  -1.751 |   0.000 |  -5.925 |
+| -0.3 |  -0.300 |   0.206 |   0.180 |  -0.108 |   0.065 |  -0.039 |   0.000 |   0.100 |  -0.855 |  -0.000 |  -4.797 |
+| -0.2 |  -0.200 |   0.095 |   0.080 |  -0.032 |   0.013 |  -0.005 |   0.000 |   0.042 |  -0.323 |   0.000 |  -3.972 |
+| -0.1 |  -0.100 |   0.024 |   0.020 |  -0.004 |   0.001 |  -0.000 |   0.000 |   0.010 |  -0.066 |  -0.000 |  -3.450 |
+| -0.0 |  -0.000 |  -0.000 |   0.000 |  -0.000 |   0.000 |  -0.000 |   0.000 |   0.000 |  -0.000 |   0.000 |   0.000 |
+|  0.1 |   0.100 |   0.024 |   0.020 |   0.004 |   0.001 |   0.000 |   0.002 |   0.010 |  -0.038 |   0.000 |  -3.046 |
+|  0.2 |   0.200 |   0.095 |   0.080 |   0.032 |   0.013 |   0.005 |   0.008 |   0.042 |  -0.093 |  -0.004 |  -2.347 |
+|  0.3 |   0.300 |   0.206 |   0.180 |   0.108 |   0.065 |   0.039 |   0.031 |   0.100 |  -0.079 |   0.024 |  -2.416 |
+|  0.4 |   0.400 |   0.345 |   0.320 |   0.256 |   0.205 |   0.164 |   0.125 |   0.200 |   0.090 |  -0.117 |   0.349 |
 |  0.5 |   0.500 |   0.500 |   0.500 |   0.500 |   0.500 |   0.500 |   1.500 |   0.500 |   0.500 |   0.500 |   0.500 |
 |  0.6 |   0.600 |   0.655 |   0.680 |   0.744 |   0.795 |   0.836 |   1.875 |   0.800 |   0.910 |   1.117 |   0.651 |
 |  0.7 |   0.700 |   0.794 |   0.820 |   0.892 |   0.935 |   0.961 |   1.969 |   0.900 |   1.079 |   0.976 |   3.416 |