**Halide is a programming language designed to make it easier to write high-performance image and array processing code on modern machines. **

halide有两个特性比较吸引人。一个是对于各种平台架构的支持。

  * CPU architectures: X86, ARM, MIPS, Hexagon, PowerPC
  * Operating systems: Linux, Windows, macOS, Android, iOS, Qualcomm QuRT
  * GPU …

迫于生计，最近要学习halide

先去学习/复习一下常见的编译优化技巧。

loop unrolling，也就是循环展开，顾名思义，就是把循环展开来写。

normal loop:
int x;
 for (x = 0; x < 100; x++)
 {
     delete(x);
 }

after loop unrolling:
int x; 
 for (x = 0; x < 100; x += 5 )
 {
     delete(x);
     delete(x + 1);
     delete(x + 2);
     delete(x + 3);
     delete(x + 4);
 }

循环展开 …