Keil C51 intrinsic function library and usage instructions

To achieve (no stack operation?), can greatly improve the access efficiency of the function.

Function prototype
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);
header file
#include

illustrate

extern void _nop_ (void);
Generates a nop instruction

extern bit_testbit_ (bit);
generates a JBC instruction, returns 1 if the bit is set, otherwise 0; can only be used for directly addressed bit variables, not for expressions

Among

extern unsigned char _cror_ (unsigned char val, unsigned char n);
(unsigned char)val right shift n bits

extern unsigned int _iror_ (unsigned int val, unsigned char n));
(unsigned int)val right shift n bits

extern unsigned long _lror_ (unsigned long val, unsigned char n));
(unsigned long)val right shift n bits

extern unsigned char _crol_ (unsigned char val, unsigned char n));
(unsigned char)val left shift n bits

extern unsigned int _irol_ (unsigned int val, unsigned char n));
(unsigned int)val left shift n bits

extern unsigned long _lrol_ (unsigned long val, unsigned char n));
(unsigned long)val left shift n bits

extern unsigned char _chkfloat_(float);
Test and return the status of float
The following is from the help document of keil C51
0 Standard floating-point numbers
1 Floating-point value 0
2 +INF (positive overflow)
3 -INF (negative overflow)
4 NaN (Not a Number) error status

References
Li Jun et al. 51 Series MCU Advanced Example Development Guide. Beijing-Beijing University of Aeronautics and Astronautics Press 2004 
Keil Software, Inc. C51 User's Guide