2020301918-os/lib/printfmt.c

#include "type.h"
#include "stdio.h"
#include "string.h"
#include "stdarg.h"

/*
 * 从xv6中抄过来的printf，感觉非常好用。
 * 支持各种常规的格式化输出，比如%d,%c,%f,%s,%u,%p
 * 这会极大的节省我们重复造输出相关轮子的时间
 */

/*
 * Print a number (base <= 16) in reverse order,
 * using specified putch function and associated pointer putdat.
 */
static void
printnum(void (*putch)(int, void*), void *putdat,
	 unsigned long long num, unsigned base, int width, int padc)
{
	// first recursively print all preceding (more significant) digits
	if (num >= base) {
		printnum(putch, putdat, num / base, base, width - 1, padc);
	} else {
		// print any needed pad characters before first digit
		while (--width > 0)
			putch(padc, putdat);
	}

	// then print this (the least significant) digit
	putch("0123456789abcdef"[num % base], putdat);
}

// Get an unsigned int of various possible sizes from a varargs list,
// depending on the lflag parameter.
static unsigned long long
getuint(va_list *ap, int lflag)
{
	if (lflag >= 2)
		return va_arg(*ap, unsigned long long);
	else if (lflag)
		return va_arg(*ap, unsigned long);
	else
		return va_arg(*ap, unsigned int);
}

// Same as getuint but signed - can't use getuint
// because of sign extension
static long long
getint(va_list *ap, int lflag)
{
	if (lflag >= 2)
		return va_arg(*ap, long long);
	else if (lflag)
		return va_arg(*ap, long);
	else
		return va_arg(*ap, int);
}

// Main function to format and print a string.
void printfmt(void (*putch)(int, void*), void *putdat, const char *fmt, ...);

void
vprintfmt(void (*putch)(int, void*), void *putdat, const char *fmt, va_list ap)
{
	register const char *p;
	register int ch, err;
	unsigned long long num;
	int base, lflag, width, precision, altflag;
	char padc;

	while (1) {
		while ((ch = *(unsigned char *) fmt++) != '%') {
			if (ch == '\0')
				return;
			putch(ch, putdat);
		}

		// Process a %-escape sequence
		padc = ' ';
		width = -1;
		precision = -1;
		lflag = 0;
		altflag = 0;
	reswitch:
		switch (ch = *(unsigned char *) fmt++) {

		// flag to pad on the right
		case '-':
			padc = '-';
			goto reswitch;

		// flag to pad with 0's instead of spaces
		case '0':
			padc = '0';
			goto reswitch;

		// width field
		case '1':
		case '2':
		case '3':
		case '4':
		case '5':
		case '6':
		case '7':
		case '8':
		case '9':
			for (precision = 0; ; ++fmt) {
				precision = precision * 10 + ch - '0';
				ch = *fmt;
				if (ch < '0' || ch > '9')
					break;
			}
			goto process_precision;

		case '*':
			precision = va_arg(ap, int);
			goto process_precision;

		case '.':
			if (width < 0)
				width = 0;
			goto reswitch;

		case '#':
			altflag = 1;
			goto reswitch;

		process_precision:
			if (width < 0)
				width = precision, precision = -1;
			goto reswitch;

		// long flag (doubled for long long)
		case 'l':
			lflag++;
			goto reswitch;

		// character
		case 'c':
			putch(va_arg(ap, int), putdat);
			break;

		// string
		case 's':
			if ((p = va_arg(ap, char *)) == NULL)
				p = "(null)";
			if (width > 0 && padc != '-')
				for (width -= strnlen(p, precision); width > 0; width--)
					putch(padc, putdat);
			for (; (ch = *p++) != '\0' && (precision < 0 || --precision >= 0); width--)
				if (altflag && (ch < ' ' || ch > '~'))
					putch('?', putdat);
				else
					putch(ch, putdat);
			for (; width > 0; width--)
				putch(' ', putdat);
			break;

		// (signed) decimal
		case 'd':
			num = getint(&ap, lflag);
			if ((long long) num < 0) {
				putch('-', putdat);
				num = -(long long) num;
			}
			base = 10;
			goto number;

		// unsigned decimal
		case 'u':
			num = getuint(&ap, lflag);
			base = 10;
			goto number;

		// (unsigned) octal
		case 'o':
			// Replace this with your code.
			putch('X', putdat);
			putch('X', putdat);
			putch('X', putdat);
			break;

		// pointer
		case 'p':
			putch('0', putdat);
			putch('x', putdat);
			num = (unsigned long long)
				(uintptr_t) va_arg(ap, void *);
			base = 16;
			goto number;

		// (unsigned) hexadecimal
		case 'x':
			num = getuint(&ap, lflag);
			base = 16;
		number:
			printnum(putch, putdat, num, base, width, padc);
			break;

		// escaped '%' character
		case '%':
			putch(ch, putdat);
			break;

		// unrecognized escape sequence - just print it literally
		default:
			putch('%', putdat);
			for (fmt--; fmt[-1] != '%'; fmt--)
				/* do nothing */;
			break;
		}
	}
}

void
printfmt(void (*putch)(int, void*), void *putdat, const char *fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	vprintfmt(putch, putdat, fmt, ap);
	va_end(ap);
}

struct sprintbuf {
	char *buf;
	char *ebuf;
	int cnt;
};

static void
sprintputch(int ch, struct sprintbuf *b)
{
	b->cnt++;
	if (b->buf < b->ebuf)
		*b->buf++ = ch;
}

int
vsnprintf(char *buf, int n, const char *fmt, va_list ap)
{
	struct sprintbuf b = {buf, buf+n-1, 0};

	if (buf == NULL || n < 1)
		return -1;

	// print the string to the buffer
	vprintfmt((void*)sprintputch, &b, fmt, ap);

	// null terminate the buffer
	*b.buf = '\0';

	return b.cnt;
}

int
snprintf(char *buf, int n, const char *fmt, ...)
{
	va_list ap;
	int rc;

	va_start(ap, fmt);
	rc = vsnprintf(buf, n, fmt, ap);
	va_end(ap);

	return rc;
}