[Java] 数値を指定の精度で切り上げ

PrecisionUtil.java

public static long ceil(long num, int precision) {
  if (num == 0) {
    return num;
  }
  int digits = calcTruncateDigits(num, precision);
  return ceilTruncate(num, digits);
}

private static int calcTruncateDigits(long num, int precision) {
  int log = (int) Math.log10(Math.abs(num));
  return log - precision + 1;
}

private static long ceilTruncate(long num, int digits) {
  if (digits <= 0) {
    return num;
  }
  long unit = (long) Math.pow(10, digits);
  long count = (long) Math.ceil((double) num / unit);
  return unit * count;
}

PrecisionUtilTest.java

@Test
public void testCeilZero() {
  assertEquals(0, ceil(0, 1));
  assertEquals(0, ceil(0, 2));
}

@Test
public void testCeil1() {
  assertEquals(1, ceil(1, 1));
  assertEquals(20, ceil(12, 1));
  assertEquals(200, ceil(123, 1));
}

@Test
public void testCeil2() {
  assertEquals(1, ceil(1, 2));
  assertEquals(12, ceil(12, 2));
  assertEquals(130, ceil(123, 2));
  assertEquals(1300, ceil(1234, 2));
}

@Test
public void testCeil3() {
  assertEquals(12, ceil(12, 3));
  assertEquals(123, ceil(123, 3));
  assertEquals(1240, ceil(1234, 3));
  assertEquals(12400, ceil(12345, 3));
}

@Test
public void testCeilMinus() {
  assertEquals(-1, ceil(-1, 1));
  assertEquals(-10, ceil(-12, 1));
  assertEquals(-12, ceil(-12, 2));
  assertEquals(-120, ceil(-123, 2));
  assertEquals(-1230, ceil(-1234, 3));
}