presto-hive/src/main/java/io/prestosql/plugin/hive/coercions/DecimalCoercers.java/LongDecimalToDoubleCoercer/applyCoercedValue
class LongDecimalToDoubleCoercer:        @Override
        protected void applyCoercedValue(BlockBuilder blockBuilder, Block block, int position)
        {
            toType.writeDouble(blockBuilder,
                    longDecimalToDouble(fromType.getSlice(block, position), fromType.getScale()));
        }