Sine.java

package ru.itmo.qa.lab2.trig;

import ch.obermuhlner.math.big.BigDecimalMath;
import ru.itmo.qa.lab2.function.AbstractFunction;

import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;

public class Sine extends AbstractFunction {

  public Sine() {
    super();
  }

  @Override
  public BigDecimal calculate(BigDecimal x, BigDecimal precision) throws ArithmeticException {
    isValid(x, precision);

    MathContext mc = new MathContext(precision.scale() + 10, RoundingMode.HALF_EVEN);

    BigDecimal pi = BigDecimalMath.pi(mc);
    BigDecimal tau = pi.multiply(BigDecimal.valueOf(2));
    x = x.remainder(tau);

    if (x.compareTo(pi) > 0) {
      x = x.subtract(tau);
    } else if (x.compareTo(pi.negate()) < 0) {
      x = x.add(tau);
    }

    BigDecimal result = x;
    BigDecimal term = x;
    BigDecimal x2 = x.multiply(x, mc);

    int i = 1;
    do {
      term = term.multiply(x2, mc)
          .divide(BigDecimal.valueOf((2L * i) * (2L * i + 1)), mc);
      result = result.add(term.multiply(minusOnePower(i)), mc);
      i++;
    } while (term.abs().compareTo(precision.divide(BigDecimal.TEN, mc)) > 0);

    return result.setScale(precision.scale(), RoundingMode.HALF_EVEN);
  }

  private static BigDecimal minusOnePower(int n) {
    return BigDecimal.valueOf(1L - (n % 2) * 2);
  }
}