对齐和性能
用于比较 char * 和 memcmp 的例程 strcmp 对于其他所有内容，它们在以某种方式对齐的内存块（在 x86_64 上）上运行速度是否更快（如何？）？ libc 是否使用 SSE 来执行此例程？
Routines strcmp for comparing char * and memcmp for everything else, do they run faster on memory block (on x86_64) which is somehow aligned (how?)? Does libc use SSE for this routines?
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这取决于对齐重要或 SIMD 指令可用的架构，通常例程将在前导字节上操作，然后执行数据允许的尽可能多的宽对齐操作，然后在尾随字节上操作。
前导字节和尾随字节是否对数据处理时间有显着影响可以通过实验来确定。
It depends, but on architectures where alignment matters or where SIMD instructions are available, typically the routines will operate on leading bytes, then do as many wide aligned operations as the data allows, then operate on trailing bytes.
Whether the leading and trailing bytes are contributing significantly to the processing time for your data can be determined by experiment.
如果您担心比较的性能，您应该看看著名的 Boyer-摩尔算法和这篇文章来自 GNU Grep 作者 Mike Haertel。
他解释了如何能够快速地在数据块中搜索某些内容。
他的总结非常清楚要做什么：
If you worry about performance for comparison, you should take a look at well-known Boyer-Moore alogrithm and this post from GNU Grep author, Mike Haertel.
He explains how one can manage to be really fast about searching something in a data block.
His summary is quite clear about what to do :