[wpimath] Add copySignPow to MathUtil for joystick input shaping (#8013)

wpimath/src/main/java/edu/wpi/first/math/MathUtil.java

@@ -107,6 +107,42 @@ public final class MathUtil {
     return applyDeadband(value, deadband, 1);
   }
 
+  /**
+   * Raises the input to the power of the given exponent while preserving its sign.
+   *
+   * <p>The function normalizes the input value to the range [0, 1] based on the maximum magnitude,
+   * raises it to the power of the exponent, then scales the result back to the original range and
+   * copying the sign. This keeps the value in the original range and gives consistent curve
+   * behavior regardless of the input value's scale.
+   *
+   * <p>This is useful for applying smoother or more aggressive control response curves (e.g.
+   * joystick input shaping).
+   *
+   * @param value The input value to transform.
+   * @param exponent The exponent to apply (e.g. 1.0 = linear, 2.0 = squared curve). Must be
+   *     positive.
+   * @param maxMagnitude The maximum expected absolute value of input. Must be positive.
+   * @return The transformed value with the same sign and scaled to the input range.
+   */
+  public static double copySignPow(double value, double exponent, double maxMagnitude) {
+    return Math.copySign(Math.pow(Math.abs(value) / maxMagnitude, exponent), value) * maxMagnitude;
+  }
+
+  /**
+   * Raises the input to the power of the given exponent while preserving its sign.
+   *
+   * <p>This is useful for applying smoother or more aggressive control response curves (e.g.
+   * joystick input shaping).
+   *
+   * @param value The input value to transform.
+   * @param exponent The exponent to apply (e.g. 1.0 = linear, 2.0 = squared curve). Must be
+   *     positive.
+   * @return The transformed value with the same sign.
+   */
+  public static double copySignPow(double value, double exponent) {
+    return copySignPow(value, exponent, 1);
+  }
+
   /**
    * Returns modulus of input.
    *