August 2017
Intermediate to advanced
360 pages
8h 35m
Chinese
Content preview from 算法技术手册（原书第2 版）
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40
｜
第
3
章
以一般都需要考虑浮点和整数运算的性能差异来优化程序。不过，相对于整数运算，现
代
CPU
已经在浮点运算上做了大量的改进和优化，即便如此，当需要使用浮点计算时，
开发人员还是需要注意这些问题（
Goldberg
，
1991
）。
3.4.1 性能
一个广为接受的观点是整数运算会比浮点运算高效得多。表
3-1
列出了在高端计算机上
进行
10 000 000
次计算的时间，这些结果包含了本书第
1
版中在
Linux
平台上的结果，
还有一台
1996
年的
Sparc Ultra-2
的结果。可以看到，单个操作的性能在不同平台上的
差异很大。而且从这些结果中，可以很明显地看出在过去
20
年左右处理器在性能上的
巨大改进。有些结果之所以为
0.0000
，是因为它们比现有的计时器还要快。
表
3
-
1
：
10
000
000
次操作的性能
操作 Sparc Ultra-
2
/s Linux i
686
/s 现代计算机/s
32 位
32 位整数 CMP 0.811 0.0337 0.0000
32 位整数 MUL 2.372 0.0421 0.0000
32 位单精度浮点数 MUL 1.236 0.1032 0.02986
64 位双精度浮点数 MUL 1.406 0.1028 0.02987
32 位单精度浮点数 DIV 1.657 0.1814 0.02982
64 位双精度浮点数 DIV 2.172 0.1813 0.02980
128 位双精度浮点数 MUL 36.891 0.2765 0.02434
32 ...
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