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# Exercise to understand double.

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Many developers fell like double' rounding and representation errors and random errors which are wild and uncontrollable.   This exercise is intended to help understand what double is really doing.

Write a method to convert double into text in a direct ByteBuffer which starts

```public static void append(ByteBuffer bb, double d) {
long val = Double.doubleToRawLongBits(d);
int sign = (int) (val >>> 63);
int exp = (int) ((val >>> 52) & 2047);
long mantissa = val & ((1L << 52) - 1);```

The goal is to write +/- 0.0001 to 100000.0 using no objects or double, just integer arithmetic.  Values outside this range can use BigDecimal or Double as a fall back.

• Implement this to convert to text the actual representation of the double, just as new BigDecimal(double) does. (Write a test which compares the values) e.g. 0.1d prints as 0.1000000000000000055511151231257827021181583404541015625
• Implement this to convert to text the closest rounded value which would have this representation as a double. i.e. 0.1d prints as 0.1
• In both cases, compare the performance with using BigDecimal and Double.toString copied to a ByteBuffer.
• Determine what is the actual range you need to use BigDecimal or Double as a fall back. Note: there is no strictly correct answer to this.
Bonus Points: Write the routine to use Unsafe and compare the performance.

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