Math Utils : Math « Development Class « Java

1. Java
2. Development Class
3. Math

Math Utils

      

//package abc.xml;

public class MathUtils {

  public static long ppcm(int a, int b) {
    return Math.abs(multiplyAndCheck(a / pgcd(a, b), b));
  }

  public static int pgcd(int u, int v) {
    if (u * v == 0) {
      return (Math.abs(u) + Math.abs(v));
    }
    // keep u and v negative, as negative integers range down to
    // -2^31, while positive numbers can only be as large as 2^31-1
    // (i.e. we can't necessarily negate a negative number without
    // overflow)
    /* assert u!=0 && v!=0; */
    if (u > 0) {
      u = -u;
    } // make u negative
    if (v > 0) {
      v = -v;
    } // make v negative
      // B1. [Find power of 2]
    int k = 0;
    while ((u & 1) == 0 && (v & 1) == 0 && k < 31) { // while u and v are
                              // both even...
      u /= 2;
      v /= 2;
      k++; // cast out twos.
    }
    if (k == 31) {
      throw new ArithmeticException("overflow: gcd is 2^31");
    }
    // B2. Initialize: u and v have been divided by 2^k and at least
    // one is odd.
    int t = ((u & 1) == 1) ? v : -(u / 2)/* B3 */;
    // t negative: u was odd, v may be even (t replaces v)
    // t positive: u was even, v is odd (t replaces u)
    do {
      /* assert u<0 && v<0; */
      // B4/B3: cast out twos from t.
      while ((t & 1) == 0) { // while t is even..
        t /= 2; // cast out twos
      }
      // B5 [reset max(u,v)]
      if (t > 0) {
        u = -t;
      } else {
        v = t;
      }
      // B6/B3. at this point both u and v should be odd.
      t = (v - u) / 2;
      // |u| larger: t positive (replace u)
      // |v| larger: t negative (replace v)
    } while (t != 0);
    return -u * (1 << k); // gcd is u*2^k
  }

  public static long multiplyAndCheck(long a, long b) {
    long ret;
    String msg = "overflow: multiply";
    if (a > b) {
      // use symmetry to reduce boundry cases
      ret = multiplyAndCheck(b, a);
    } else {
      if (a < 0) {
        if (b < 0) {
          // check for positive overflow with negative a, negative b
          if (a >= Long.MAX_VALUE / b) {
            ret = a * b;
          } else {
            throw new ArithmeticException(msg);
          }
        } else if (b > 0) {
          // check for negative overflow with negative a, positive b
          if (Long.MIN_VALUE / b <= a) {
            ret = a * b;
          } else {
            throw new ArithmeticException(msg);

          }
        } else {
          // assert b == 0
          ret = 0;
        }
      } else if (a > 0) {
        // assert a > 0
        // assert b > 0

        // check for positive overflow with positive a, positive b
        if (a <= Long.MAX_VALUE / b) {
          ret = a * b;
        } else {
          throw new ArithmeticException(msg);
        }
      } else {
        // assert a == 0
        ret = 0;
      }
    }
    return ret;
  }

}

   
    
    
    
    
    
  

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