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javabigdecimal

Working with large numbers

When I do the following calculation (97 ^ 23) mod 187 in Java:

double ret = (Math.pow (97, 23))% 187;

ret value is 74. The value of (Math.Pow (97, 23)) is 4.963064143419832E45;

My problem is the following: the value of the expression (97 ^ 23) mod 187 = 58. Try to do the windows calculator. I've tried using BigDecimal and still can not get the value I need.

Making (97 ^ 23) in the windows calculator it returns 4.9630641434198319969863989680919 +45 and so much more precise.

If someone can help me, thank you very much!

Solution

  • Modular power is implemented in the BigInteger class:

    BigInteger a = new BigInteger("97");
BigInteger x = new BigInteger("23");
BigInteger m = new BigInteger("187");
BigInteger result = a.modPow(x, m); // 97^23 % 187

    To get the result as an int you can use the intValue() method.