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javabigdecimal

scale keeps growing beyond math context precision

I am working on some code that calculates points on a 2 axis graph and I noticed that when the X or Y coordinate was value zero it slowed down. I spit out some debug and found that the scale of my coordinate value was continually growing. I thought passing the math context would make the return bigdecimal not be able to have a larger scale. I was hoping to limit the scale to my math context precision. This code shows what I am seeing. 

MathContext mc = new MathContext(32);
BigDecimal xPos = new BigDecimal("0.0", mc);
for (int i = 0; i < 8; i++)
{
    System.out.println("" + xPos + " scale=" + xPos.scale());
    xPos = xPos.multiply(xPos, mc);
}

The scale continues to increase with each iteration. Am I incorrect in thinking that because I pass multiply a math context that it should limit the precision of the return? Thanks for reading.

Solution

  • It's all explained in the BigDecimal API.

    Operation     Preferred Scale of Result

Add           max(addend.scale(), augend.scale())
Subtract      max(minuend.scale(), subtrahend.scale())
Multiply      multiplier.scale() + multiplicand.scale()
Divide        dividend.scale() - divisor.scale()

    And it makes sense in a logarithmic sort of way.