c - 重复完全相同的代码段 1000 次而不循环

Question

出于某种原因(与性能测量相关)，我需要重复代码段 1000 次(1024 次也可以)，但没有“for”或任何其他循环。

显然，我很可能编写一个如下所示的宏:

#define RUN_1000_TIMES(x)   \
x                           \
x                           \
x                           \
...
...  /* (999+1 times the same line) */
...
x                           \
x

...然后将该宏应用到我的代码段。

但是还有比 1000 行长宏更优雅的解决方案吗？

Answer 1

#define RUN_1024_TIMES(x) do {RUN_512_TIMES(x); RUN_512_TIMES(x); } while(0)
#define RUN_512_TIMES(x) do {RUN_256_TIMES(x); RUN_256_TIMES(x); } while(0)
#define RUN_256_TIMES(x) do {RUN_128_TIMES(x); RUN_128_TIMES(x); } while(0)
#define RUN_128_TIMES(x) do {RUN_64_TIMES(x); RUN_64_TIMES(x); } while(0)
#define RUN_64_TIMES(x) do {RUN_32_TIMES(x); RUN_32_TIMES(x); } while(0)
#define RUN_32_TIMES(x) do {RUN_16_TIMES(x); RUN_16_TIMES(x); } while(0)
#define RUN_16_TIMES(x) do {RUN_8_TIMES(x); RUN_8_TIMES(x); } while(0)
#define RUN_8_TIMES(x) do {RUN_4_TIMES(x); RUN_4_TIMES(x); } while(0)
#define RUN_4_TIMES(x) do {RUN_2_TIMES(x); RUN_2_TIMES(x); } while(0)
#define RUN_2_TIMES(x) do {x; x; } while(0)

do{ ... } while(0)仅适用于您使用 if (....) RUN_1024_TIMES(...); 调用它的情况。不需要时可以将其删除。

您也可以对每个宏执行 3 次:

#define RUN_1000_TIMES(x) do {RUN_729_TIMES(x); RUN_243_TIMES(x); RUN_27_TIMES(x); x; } while(0)
#define RUN_729_TIMES(x) do {RUN_243_TIMES(x); RUN_243_TIMES(x); RUN_243_TIMES(x); } while(0)
#define RUN_243_TIMES(x) do {RUN_81_TIMES(x); RUN_81_TIMES(x); RUN_81_TIMES(x); } while(0)
#define RUN_81_TIMES(x) do {RUN_27_TIMES(x); RUN_27_TIMES(x); RUN_27_TIMES(x); } while(0)
#define RUN_27_TIMES(x) do {RUN_9_TIMES(x); RUN_9_TIMES(x); RUN_9_TIMES(x); } while(0)
#define RUN_9_TIMES(x) do {RUN_3_TIMES(x); RUN_3_TIMES(x); RUN_3_TIMES(x); } while(0)
#define RUN_3_TIMES(x) do {x; x; x; } while(0)