fmt.c

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

#include <u.h>
#include <libc.h>
#include "fmtdef.h"

enum
{
	Maxfmt = 64
};

typedef struct Convfmt Convfmt;
struct Convfmt
{
	int	c;
	volatile	Fmts	fmt;	/* for spin lock in fmtfmt; avoids race due to write order */
};

struct
{
	/* lock by calling _fmtlock, _fmtunlock */
	int	nfmt;
	Convfmt	fmt[Maxfmt];
} fmtalloc;

static Convfmt knownfmt[] = {
	' ',	_flagfmt,
	'#',	_flagfmt,
	'%',	_percentfmt,
	'+',	_flagfmt,
	',',	_flagfmt,
	'-',	_flagfmt,
	'C',	_runefmt,
	'E',	_efgfmt,
	'G',	_efgfmt,
	'S',	_runesfmt,
	'X',	_ifmt,
	'b',	_ifmt,
	'c',	_charfmt,
	'd',	_ifmt,
	'e',	_efgfmt,
	'f',	_efgfmt,
	'g',	_efgfmt,
	'h',	_flagfmt,
	'l',	_flagfmt,
	'n',	_countfmt,
	'o',	_ifmt,
	'p',	_ifmt,
	'r',	errfmt,
	's',	_strfmt,
	'u',	_flagfmt,
	'x',	_ifmt,
	0,	nil,
};

int	(*doquote)(int);

/*
 * _fmtlock() must be set
 */
static int
_fmtinstall(int c, Fmts f)
{
	Convfmt *p, *ep;

	if(c<=0 || c>=65536)
		return -1;
	if(!f)
		f = _badfmt;

	ep = &fmtalloc.fmt[fmtalloc.nfmt];
	for(p=fmtalloc.fmt; p<ep; p++)
		if(p->c == c)
			break;

	if(p == &fmtalloc.fmt[Maxfmt])
		return -1;

	p->fmt = f;
	if(p == ep){	/* installing a new format character */
		fmtalloc.nfmt++;
		p->c = c;
	}

	return 0;
}

int
fmtinstall(int c, Fmts f)
{
	int ret;

	_fmtlock();
	ret = _fmtinstall(c, f);
	_fmtunlock();
	return ret;
}

static Fmts
fmtfmt(int c)
{
	Convfmt *p, *ep;

	ep = &fmtalloc.fmt[fmtalloc.nfmt];
	for(p=fmtalloc.fmt; p<ep; p++)
		if(p->c == c){
			while(p->fmt == nil)	/* loop until value is updated */
				;
			return p->fmt;
		}

	/* is this a predefined format char? */
	_fmtlock();
	for(p=knownfmt; p->c; p++)
		if(p->c == c){
			_fmtinstall(p->c, p->fmt);
			_fmtunlock();
			return p->fmt;
		}
	_fmtunlock();

	return _badfmt;
}

void*
_fmtdispatch(Fmt *f, void *fmt, int isrunes)
{
	Rune rune, r;
	int i, n;

	f->flags = 0;
	f->width = f->prec = 0;

	for(;;){
		if(isrunes){
			r = *(Rune*)fmt;
			fmt = (Rune*)fmt + 1;
		}else{
			fmt = (char*)fmt + chartorune(&rune, fmt);
			r = rune;
		}
		f->r = r;
		switch(r){
		case '\0':
			return nil;
		case '.':
			f->flags |= FmtWidth|FmtPrec;
			continue;
		case '0':
			if(!(f->flags & FmtWidth)){
				f->flags |= FmtZero;
				continue;
			}
			/* fall through */
		case '1': case '2': case '3': case '4':
		case '5': case '6': case '7': case '8': case '9':
			i = 0;
			while(r >= '0' && r <= '9'){
				i = i * 10 + r - '0';
				if(isrunes){
					r = *(Rune*)fmt;
					fmt = (Rune*)fmt + 1;
				}else{
					r = *(char*)fmt;
					fmt = (char*)fmt + 1;
				}
			}
			if(isrunes)
				fmt = (Rune*)fmt - 1;
			else
				fmt = (char*)fmt - 1;
		numflag:
			if(f->flags & FmtWidth){
				f->flags |= FmtPrec;
				f->prec = i;
			}else{
				f->flags |= FmtWidth;
				f->width = i;
			}
			continue;
		case '*':
			i = va_arg(f->args, int);
			if(i < 0){
				/*
				 * negative precision =>
				 * ignore the precision.
				 */
				if(f->flags & FmtPrec){
					f->flags &= ~FmtPrec;
					f->prec = 0;
					continue;
				}
				i = -i;
				f->flags |= FmtLeft;
			}
			goto numflag;
		}
		n = (*fmtfmt(r))(f);
		if(n < 0)
			return nil;
		if(n == 0)
			return fmt;
	}
}