java在BigDecimal#divide()中的“scale”越高,速度越快?
我提出了一个问题,最初是一个问答式的问题
原来的问题是:
在BigDecimal#divide()
中较高的scale
对性能有多大影响
所以,我创建了这个SSCCE:
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.concurrent.TimeUnit;
public class Test {
public static void main(String args[]) {
int[] scales = new int[] {1, 10, 50, 100, 500, 1000, 5000, 100000, 1000000};
for(Integer scale : scales) {
long start = System.nanoTime();
BigDecimal.ONE.divide(BigDecimal.valueOf(7), scale, RoundingMode.HALF_UP);
long end = System.nanoTime();
long elapsed = end - start;
String elapsed_str = String.format("%d mins, %d secs, %d millis, %d nanos",
TimeUnit.NANOSECONDS.toMinutes(elapsed),
TimeUnit.NANOSECONDS.toSeconds(elapsed) - TimeUnit.MINUTES.toSeconds(TimeUnit.NANOSECONDS.toMinutes(elapsed)),
TimeUnit.NANOSECONDS.toMillis(elapsed) - TimeUnit.SECONDS.toMillis(TimeUnit.NANOSECONDS.toSeconds(elapsed)),
elapsed - TimeUnit.MILLISECONDS.toNanos(TimeUnit.NANOSECONDS.toMillis(elapsed))
);
System.out.println("Time for scale = " + scale + ": " + elapsed_str);
}
}
}
结果是:
Time for scale = 1: 0 mins, 0 secs, 2 millis, 883903 nanos
Time for scale = 10: 0 mins, 0 secs, 0 millis, 13995 nanos
Time for scale = 50: 0 mins, 0 secs, 1 millis, 138727 nanos
Time for scale = 100: 0 mins, 0 secs, 0 millis, 645636 nanos
Time for scale = 500: 0 mins, 0 secs, 1 millis, 250220 nanos
Time for scale = 1000: 0 mins, 0 secs, 4 millis, 38957 nanos
Time for scale = 5000: 0 mins, 0 secs, 15 millis, 66549 nanos
Time for scale = 100000: 0 mins, 0 secs, 500 millis, 873987 nanos
Time for scale = 1000000: 0 mins, 50 secs, 183 millis, 686684 nanos
随着数量级的增加,性能会受到指数级的影响。但让我挠头的是这些台词:
Time for scale = 1: 0 mins, 0 secs, 2 millis, 883903 nanos
Time for scale = 10: 0 mins, 0 secs, 0 millis, 13995 nanos
Time for scale = 50: 0 mins, 0 secs, 1 millis, 138727 nanos
Time for scale = 100: 0 mins, 0 secs, 0 millis, 645636 nanos
Time for scale = 500: 0 mins, 0 secs, 1 millis, 250220 nano
看来10
的尺度对于BigDecimal#divide()
来说是最佳的?而且100
的规模比50
快?我认为这可能只是一个异常,所以我再次运行它(这次,省略了最高的两个刻度,因为我不想等待50秒:),结果如下:
Time for scale = 1: 0 mins, 0 secs, 3 millis, 440903 nanos
Time for scale = 10: 0 mins, 0 secs, 0 millis, 10263 nanos
Time for scale = 50: 0 mins, 0 secs, 0 millis, 833169 nanos
Time for scale = 100: 0 mins, 0 secs, 0 millis, 487492 nanos
Time for scale = 500: 0 mins, 0 secs, 0 millis, 802846 nanos
Time for scale = 1000: 0 mins, 0 secs, 2 millis, 475715 nanos
Time for scale = 5000: 0 mins, 0 secs, 16 millis, 646117 nanos
同样地,10
比1
快得多,100
比50
快得多
我试了一次又一次,结果100
总是比50
快。而且1
的尺度总是比小于1000
的任何事物都慢
有人有解释吗
共 (0) 个答案