keil C51中的本征函数库及使用说明

来实现(无需堆栈操作?),可大大提高函数的访问效率.

函数原型
extern void          _nop_     (void);
extern bit           _testbit_ (bit);
extern unsigned char _cror_    (unsigned char, unsigned char);
extern unsigned int  _iror_    (unsigned int,  unsigned char);
extern unsigned long _lror_    (unsigned long, unsigned char);
extern unsigned char _crol_    (unsigned char, unsigned char);
extern unsigned int  _irol_    (unsigned int,  unsigned char);
extern unsigned long _lrol_    (unsigned long, unsigned char);
extern unsigned char _chkfloat_(float);
头文件
#include

说明

extern void          _nop_     (void);
产生一个nop指令

extern bit_testbit_ (bit);
产生一个JBC指令,若该位置位,返回1,否则为0;只能作用于直接寻址的位变量,不能用于表达式

之中

extern unsigned char _cror_    (unsigned char val, unsigned char n);
(unsigned char)val右移n位

extern unsigned int  _iror_    (unsigned int val, unsigned char n));
(unsigned int)val右移n位

extern unsigned long _lror_    (unsigned long val, unsigned char n));
(unsigned long)val右移n位

extern unsigned char _crol_    (unsigned char val, unsigned char n));
(unsigned char)val左移n位

extern unsigned int  _irol_    (unsigned int val, unsigned char n));
(unsigned int)val左移n位

extern unsigned long _lrol_    (unsigned long val, unsigned char n));
(unsigned long)val左移n位

extern unsigned char _chkfloat_(float);
测试并返回float的状态
一下摘自keil C51的帮助文档
0 Standard floating-point numbers 标准浮点数
1 Floating-point value 0 浮点数0
2 +INF (positive overflow) 正溢出
3 -INF (negative overflow) 负溢出
4 NaN (Not a Number) error status出错

参考文献
李军等编著.51系列单片机高级实例开发指南.北京-北京航空航天大学出版社 2004 
keil software,inc.  C51 user's guide