whack.h

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

typedef struct Whack		Whack;
typedef struct Unwhack		Unwhack;

enum
{
	WhackStats	= 8,
	WhackErrLen	= 64,		/* max length of error message from thwack or unthwack */
	WhackMaxOff	= 16*1024,	/* max allowed offset */

	HashLog		= 14,
	HashSize	= 1<<HashLog,
	HashMask	= HashSize - 1,

	MinMatch	= 3,		/* shortest match possible */

	MinDecode	= 8,		/* minimum bits to decode a match or lit; >= 8 */

	MaxSeqMask	= 8,		/* number of bits in coding block mask */
	MaxSeqStart	= 256		/* max offset of initial coding block */
};

struct Whack
{
	ushort		begin;			/* time of first byte in hash */
	ushort		hash[HashSize];
	ushort		next[WhackMaxOff];
	uchar		*data;
};

struct Unwhack
{
	char		err[WhackErrLen];
};

void	whackinit(Whack*, int level);
void	unwhackinit(Unwhack*);
int	whack(Whack*, uchar *dst, uchar *src, int nsrc, ulong stats[WhackStats]);
int	unwhack(Unwhack*, uchar *dst, int ndst, uchar *src, int nsrc);

int	whackblock(uchar *dst, uchar *src, int ssize);