bitop.h

代码有点长,需细心阅读,仅供影音视听类产品的开发人员参考

#ifndef	__BITOP_H
#define	__BITOP_H

// revn(): reverse #n LSB bit order
unsigned revn(unsigned u, int n);

//
// getbits utility for gunzip
// *note* this getbits utility is:
// 1. byte-oriented
// 2. LSB first
//

// t_getbit
typedef struct
{
	BYTE   *p;
	int     r;
}
t_getbit;

// showbits()
unsigned showbit(t_getbit * p);

// dumpbits()
#define	dumpbits(p,n)	(((p)->r)+=(n))

// getbits_bytealign()
static  inline void getbits_bytealign(t_getbit * p)
{
	p->r = (p->r + 7) & ~7;
}

// maskbit()
static  inline unsigned maskbit(unsigned b, unsigned n)
{
	return (b & (0x7fffffffu >> (31 - n)));
}

// getbits()
static inline unsigned getbits(t_getbit * p, int n)
{
	unsigned v = maskbit(showbit(p), n);

	dumpbits(p, n);
	return v;
}

// getbits_init()
static inline void getbits_init(t_getbit * p, const void *ptr)
{
	p->p = (BYTE *) ptr;					// initialize input pointer
	p->r = 0;											// initialize input bit-pointer
}

//
// gunzip()
// return <0 value for failure within gunzip process
// you need to initialize getbits structure before this.
//
int     gunzip(t_getbit * gb, BYTE * op);

#endif /*BITOP_H */