Optimize the binaryToDecimal function in the DecimalUtils class

[qian0817]

Describe the enhancement requested

https://github.com/apache/parquet-java/blob/master/parquet-pig/src/main/java/org/apache/parquet/pig/convert/DecimalUtils.java

 public static BigDecimal binaryToDecimal(Binary value, int precision, int scale) {
 /*
 * Precision <= 18 checks for the max number of digits for an unscaled long,
 * else treat with big integer conversion
 */
 if (precision <= 18) {
 ByteBuffer buffer = value.toByteBuffer();
 byte[] bytes = buffer.array();
 int start = buffer.arrayOffset() + buffer.position();
 int end = buffer.arrayOffset() + buffer.limit();
 long unscaled = 0L;
 int i = start;
 while (i < end) {
 unscaled = (unscaled << 8 | bytes[i] & 0xff);
 i++;
 }
 int bits = 8 * (end - start);
 long unscaledNew = (unscaled << (64 - bits)) >> (64 - bits);
 if (unscaledNew <= -pow(10, 18) || unscaledNew >= pow(10, 18)) {
 return new BigDecimal(unscaledNew);
 } else {
 return BigDecimal.valueOf(unscaledNew / pow(10, scale));
 }
 } else {
 return new BigDecimal(new BigInteger(value.getBytes()), scale);
 }
 }

If precision is less than 18, the condition unscaledNew <= -pow(10, 18) || unscaledNew >= pow(10, 18) can not be true, so we can remove the judgment logic here. Additionally, using BigDecimal.valueOf(unscaledNew, scale) is preferable over using BigDecimal.valueOf(unscaledNew / pow(10, scale)), as it does not convert the unscaled value to double.

Component(s)

No response