Relates :


Relates :

Summary  Optimize `java.text.DecimalFormat.format` by taking advantage of numerical properties of integer and floatingpoint arithmetic to accelerate cases with two or three digits after the decimal point. Goals  Make common usages of `DecimalFormat` faster. Success Metrics  At least a 2X speedup on microbenchmarks of interest. Description  The decimal format conversions of most interest are for those with two and three digits after the decimal point. Rather than perform expensive floatingpoint divisions to isolate and round the fractional digits, a floatingpoint multiply of the fractional portion by 100.0 or 1000.0 can be performed, the product converted to an integer value, and then the resulting integer converted to decimal. While this process is faster, care must be taken to avoid doublerounding and other numerical hazards. Case analysis using properties of which fractional decimal values can be exactly represented in binary reduces rounding postmultiply to a look up table style computation. Testing  Besides running existing JCK and regression tests, new tests targeting the boundary cases of the optimized code path will be developed. In addition, the performance of the code will be assessed using microbenchmarks on contemporary hardware platforms. Risks and Assumptions  Exploratory work with the optimized implementation revealing a longstanding numerical bug in `DecimalFormat`: some near halfway cases did not round correctly. The specification of `DecimalFormat` is being amended in Java SE 8 to clearly require correct rounding all the time. Impact   Compatibility: On JDK 7, (correct) but altered numerical behavior will only be enabled under an aggressive optimization flag to limit behavioral compatibility impact in that release train. In Java SE 8, the correct numerical behavior will always be required by the specification.  Performance/scalability: Many common cases will go faster with the new algorithm; other cases will fall back to using the older code.  TCK: Some new test cases in JCK 8 would be helpful.