shift count is too large

STM8S是8 bit单片机
在STM8S中 unsigned long是32位， unsigned short和unsigned int都是16位，unsigned char是8位。

以以下代码编译时报了“shift count is too large”的warning， 并且代码执行时也没有达到预期效果：

 unsigned char temp[];
 unsigned long pd_reg;
 ...
 pd_reg = temp[] <<  | temp[] <<  | temp[] <<  | temp[];

后面加上了强制类型转换解决了此问题：

 unsigned char temp[];
 unsigned long pd_reg;
 ...
 pd_reg = (unsigned long)temp[] <<  | (unsigned long)temp[] <<  | (unsigned long)temp[] <<  | (unsigned long)temp[];