xref: /csrg-svn/lib/libc/stdio/vfprintf.c (revision 46442)

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Chris Torek.
 *
 * %sccs.include.redist.c%
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)vfprintf.c	5.44 (Berkeley) 02/16/91";
#endif /* LIBC_SCCS and not lint */

/*
 * Actual printf innards.
 *
 * This code is large and complicated...
 */

#include <sys/types.h>
#include <stdio.h>
#include <string.h>
#if __STDC__
#include <stdarg.h>
#else
#include <varargs.h>
#endif
#include "local.h"
#include "fvwrite.h"

/*
 * Define FLOATING_POINT to get floating point.
 * Define CSH to get a csh-specific version (grr).
 */
#ifndef CSH
#define	FLOATING_POINT
#endif

/* end of configuration stuff */


#ifdef CSH
/*
 * C shell hacks.  Ick, gag.
 */
#undef BUFSIZ
#include "sh.h"

#if __STDC__
int
printf(const char *fmt, ...) {
	FILE f;

	f._flags = __SWR;
	return (vfprintf(&f, fmt, (va_list)(&fmt + 1)));
}
#else
int
printf(fmt, args)
	char *fmt;
{
	FILE f;

	f._flags = __SWR;
	f._write = NULL;
	return (vfprintf(&f, fmt, &args));
}
#endif

int
__sprint(fp, uio)
	FILE *fp;
	register struct __suio *uio;
{
	register char *p;
	register int n, ch, iovcnt;
	register struct __siov *iov;

	/* must allow sprintf to work, might as well allow others too */
	if (fp->_write || fp->_flags & __SSTR) {
		if (uio->uio_resid == 0) {
			uio->uio_iovcnt = 0;
			return (0);
		}
		n = __sfvwrite(fp, uio);
		uio->uio_resid = 0;
		uio->uio_iovcnt = 0;
		return (n);
	}
	iov = uio->uio_iov;
	for (iovcnt = uio->uio_iovcnt; --iovcnt >= 0; iov++) {
		for (p = iov->iov_base, n = iov->iov_len; --n >= 0;) {
#ifdef CSHPUTCHAR
			ch = *p++;
			CSHPUTCHAR;	/* this horrid macro uses `ch' */
#else
#undef putchar
			putchar(*p++);
#endif
		}
	}
	uio->uio_resid = 0;
	uio->uio_iovcnt = 0;
	return (0);
}

#else /* CSH */

/*
 * Flush out all the vectors defined by the given uio,
 * then reset it so that it can be reused.
 */
static int
__sprint(fp, uio)
	FILE *fp;
	register struct __suio *uio;
{
	register int err;

	if (uio->uio_resid == 0) {
		uio->uio_iovcnt = 0;
		return (0);
	}
	err = __sfvwrite(fp, uio);
	uio->uio_resid = 0;
	uio->uio_iovcnt = 0;
	return (err);
}

/*
 * Helper function for `fprintf to unbuffered unix file': creates a
 * temporary buffer.  We only work on write-only files; this avoids
 * worries about ungetc buffers and so forth.
 */
static int
__sbprintf(fp, fmt, ap)
	register FILE *fp;
	const char *fmt;
	va_list ap;
{
	int ret;
	FILE fake;
	unsigned char buf[BUFSIZ];

	/* copy the important variables */
	fake._flags = fp->_flags & ~__SNBF;
	fake._file = fp->_file;
	fake._cookie = fp->_cookie;
	fake._write = fp->_write;

	/* set up the buffer */
	fake._bf._base = fake._p = buf;
	fake._bf._size = fake._w = sizeof(buf);
	fake._lbfsize = 0;	/* not actually used, but Just In Case */

	/* do the work, then copy any error status */
	ret = vfprintf(&fake, fmt, ap);
	if (ret >= 0 && fflush(&fake))
		ret = EOF;
	if (fake._flags & __SERR)
		fp->_flags |= __SERR;
	return (ret);
}

#endif /* CSH */


#ifdef FLOATING_POINT
#include "floatio.h"

#define	BUF		(MAXEXP+MAXFRACT+1)	/* + decimal point */
#define	DEFPREC		6

static int cvt();
#if defined(hp300) || defined(sparc)
static char *isspecial();
#endif

#else /* no FLOATING_POINT */

#define	BUF		40

#endif /* FLOATING_POINT */


/*
 * Macros for converting digits to letters and vice versa
 */
#define	to_digit(c)	((c) - '0')
#define is_digit(c)	((unsigned)to_digit(c) <= 9)
#define	to_char(n)	((n) + '0')

/*
 * Flags used during conversion.
 */
#define	LONGINT		0x01		/* long integer */
#define	LONGDBL		0x02		/* long double; unimplemented */
#define	SHORTINT	0x04		/* short integer */
#define	ALT		0x08		/* alternate form */
#define	LADJUST		0x10		/* left adjustment */
#define	ZEROPAD		0x20		/* zero (as opposed to blank) pad */
#define	HEXPREFIX	0x40		/* add 0x or 0X prefix */

int
vfprintf(fp, fmt0, ap)
	FILE *fp;
	const char *fmt0;
#if tahoe
 register /* technically illegal, since we do not know what type va_list is */
#endif
	va_list ap;
{
	register char *fmt;	/* format string */
	register int ch;	/* character from fmt */
	register int n;		/* handy integer (short term usage) */
	register char *cp;	/* handy char pointer (short term usage) */
	register struct __siov *iovp;/* for PRINT macro */
	register int flags;	/* flags as above */
	int ret;		/* return value accumulator */
	int width;		/* width from format (%8d), or 0 */
	int prec;		/* precision from format (%.3d), or -1 */
	char sign;		/* sign prefix (' ', '+', '-', or \0) */
#ifdef FLOATING_POINT
	char softsign;		/* temporary negative sign for floats */
	double _double;		/* double precision arguments %[eEfgG] */
	int fpprec;		/* `extra' floating precision in [eEfgG] */
#endif
	u_long _ulong;		/* integer arguments %[diouxX] */
	enum { OCT, DEC, HEX } base;/* base for [diouxX] conversion */
	int dprec;		/* a copy of prec if [diouxX], 0 otherwise */
	int fieldsz;		/* field size expanded by sign, etc */
	int realsz;		/* field size expanded by dprec */
	int size;		/* size of converted field or string */
	char *xdigs;		/* digits for [xX] conversion */
#define NIOV 8
	struct __suio uio;	/* output information: summary */
	struct __siov iov[NIOV];/* ... and individual io vectors */
	char buf[BUF];		/* space for %c, %[diouxX], %[eEfgG] */
	char ox[2];		/* space for 0x hex-prefix */

	/*
	 * Choose PADSIZE to trade efficiency vs size.  If larger
	 * printf fields occur frequently, increase PADSIZE (and make
	 * the initialisers below longer).
	 */
#define	PADSIZE	16		/* pad chunk size */
	static char blanks[PADSIZE] =
	 {' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' '};
	static char zeroes[PADSIZE] =
	 {'0','0','0','0','0','0','0','0','0','0','0','0','0','0','0','0'};

	/*
	 * BEWARE, these `goto error' on error, and PAD uses `n'.
	 */
#define	PRINT(ptr, len) { \
	iovp->iov_base = (ptr); \
	iovp->iov_len = (len); \
	uio.uio_resid += (len); \
	iovp++; \
	if (++uio.uio_iovcnt >= NIOV) { \
		if (__sprint(fp, &uio)) \
			goto error; \
		iovp = iov; \
	} \
}
#define	PAD(howmany, with) { \
	if ((n = (howmany)) > 0) { \
		while (n > PADSIZE) { \
			PRINT(with, PADSIZE); \
			n -= PADSIZE; \
		} \
		PRINT(with, n); \
	} \
}
#define	FLUSH() { \
	if (uio.uio_resid && __sprint(fp, &uio)) \
		goto error; \
	uio.uio_iovcnt = 0; \
	iovp = iov; \
}

	/*
	 * To extend shorts properly, we need both signed and unsigned
	 * argument extraction methods.
	 */
#define	SARG() \
	(flags&LONGINT ? va_arg(ap, long) : \
	    flags&SHORTINT ? (long)(short)va_arg(ap, int) : \
	    (long)va_arg(ap, int))
#define	UARG() \
	(flags&LONGINT ? va_arg(ap, u_long) : \
	    flags&SHORTINT ? (u_long)(u_short)va_arg(ap, int) : \
	    (u_long)va_arg(ap, u_int))

#ifndef CSH
	/* sorry, fprintf(read_only_file, "") returns EOF, not 0 */
	if (cantwrite(fp))
		return (EOF);

	/* optimise fprintf(stderr) (and other unbuffered Unix files) */
	if ((fp->_flags & (__SNBF|__SWR|__SRW)) == (__SNBF|__SWR) &&
	    fp->_file >= 0)
		return (__sbprintf(fp, fmt0, ap));
#endif /* CSH */

	fmt = (char *)fmt0;
	uio.uio_iov = iovp = iov;
	uio.uio_resid = 0;
	uio.uio_iovcnt = 0;
	ret = 0;

	/*
	 * Scan the format for conversions (`%' character).
	 */
	for (;;) {
		for (cp = fmt; (ch = *fmt) != '\0' && ch != '%'; fmt++)
			/* void */;
		if ((n = fmt - cp) != 0) {
			PRINT(cp, n);
			ret += n;
		}
		if (ch == '\0')
			goto done;
		fmt++;		/* skip over '%' */

		flags = 0;
		dprec = 0;
#ifdef FLOATING_POINT
		fpprec = 0;
#endif
		width = 0;
		prec = -1;
		sign = '\0';

rflag:		ch = *fmt++;
reswitch:	switch (ch) {
		case ' ':
			/*
			 * ``If the space and + flags both appear, the space
			 * flag will be ignored.''
			 *	-- ANSI X3J11
			 */
			if (!sign)
				sign = ' ';
			goto rflag;
		case '#':
			flags |= ALT;
			goto rflag;
		case '*':
			/*
			 * ``A negative field width argument is taken as a
			 * - flag followed by a positive field width.''
			 *	-- ANSI X3J11
			 * They don't exclude field widths read from args.
			 */
			if ((width = va_arg(ap, int)) >= 0)
				goto rflag;
			width = -width;
			/* FALLTHROUGH */
		case '-':
			flags |= LADJUST;
			goto rflag;
		case '+':
			sign = '+';
			goto rflag;
		case '.':
			if ((ch = *fmt++) == '*') {
				n = va_arg(ap, int);
				prec = n < 0 ? -1 : n;
				goto rflag;
			}
			n = 0;
			while (is_digit(ch)) {
				n = 10 * n + to_digit(ch);
				ch = *fmt++;
			}
			prec = n < 0 ? -1 : n;
			goto reswitch;
		case '0':
			/*
			 * ``Note that 0 is taken as a flag, not as the
			 * beginning of a field width.''
			 *	-- ANSI X3J11
			 */
			flags |= ZEROPAD;
			goto rflag;
		case '1': case '2': case '3': case '4':
		case '5': case '6': case '7': case '8': case '9':
			n = 0;
			do {
				n = 10 * n + to_digit(ch);
				ch = *fmt++;
			} while (is_digit(ch));
			width = n;
			goto reswitch;
#ifdef FLOATING_POINT
		case 'L':
			flags |= LONGDBL;
			goto rflag;
#endif
		case 'h':
			flags |= SHORTINT;
			goto rflag;
		case 'l':
			flags |= LONGINT;
			goto rflag;
		case 'c':
			*(cp = buf) = va_arg(ap, int);
			size = 1;
			sign = '\0';
			break;
		case 'D':
			flags |= LONGINT;
			/*FALLTHROUGH*/
		case 'd':
		case 'i':
			_ulong = SARG();
			if ((long)_ulong < 0) {
				_ulong = -_ulong;
				sign = '-';
			}
			base = DEC;
			goto number;
#ifdef FLOATING_POINT
		case 'e':
		case 'E':
		case 'f':
		case 'g':
		case 'G':
			_double = va_arg(ap, double);
#if defined(hp300) || defined(sparc)
			/* do this before tricky precision changes */
			if ((cp = isspecial(_double, &sign)) != NULL) {
				size = strlen(cp);
				break;
			}
#endif
			/*
			 * don't do unrealistic precision; just pad it with
			 * zeroes later, so buffer size stays rational.
			 */
			if (prec > MAXFRACT) {
				if (ch != 'g' && ch != 'G' || (flags&ALT))
					fpprec = prec - MAXFRACT;
				prec = MAXFRACT;
			} else if (prec == -1)
				prec = DEFPREC;
			/*
			 * cvt may have to round up before the "start" of
			 * its buffer, i.e. ``intf("%.2f", (double)9.999);'';
			 * if the first character is still NUL, it did.
			 * softsign avoids negative 0 if _double < 0 but
			 * no significant digits will be shown.
			 */
			cp = buf;
			*cp = '\0';
			size = cvt(_double, prec, flags, &softsign, ch,
			    cp, buf + sizeof(buf));
			if (softsign)
				sign = '-';
			if (*cp == '\0')
				cp++;
			break;
#endif /* FLOATING_POINT */
		case 'n':
			if (flags & LONGINT)
				*va_arg(ap, long *) = ret;
			else if (flags & SHORTINT)
				*va_arg(ap, short *) = ret;
			else
				*va_arg(ap, int *) = ret;
			continue;	/* no output */
		case 'O':
			flags |= LONGINT;
			/*FALLTHROUGH*/
		case 'o':
			_ulong = UARG();
			base = OCT;
			goto nosign;
		case 'p':
			/*
			 * ``The argument shall be a pointer to void.  The
			 * value of the pointer is converted to a sequence
			 * of printable characters, in an implementation-
			 * defined manner.''
			 *	-- ANSI X3J11
			 */
			/* NOSTRICT */
			_ulong = (u_long)va_arg(ap, void *);
			base = HEX;
			xdigs = "0123456789abcdef";
			flags |= HEXPREFIX;
			ch = 'x';
			goto nosign;
		case 's':
			if ((cp = va_arg(ap, char *)) == NULL)
				cp = "(null)";
			if (prec >= 0) {
				/*
				 * can't use strlen; can only look for the
				 * NUL in the first `prec' characters, and
				 * strlen() will go further.
				 */
				char *p = memchr(cp, 0, prec);

				if (p != NULL) {
					size = p - cp;
					if (size > prec)
						size = prec;
				} else
					size = prec;
			} else
				size = strlen(cp);
			sign = '\0';
			break;
		case 'U':
			flags |= LONGINT;
			/*FALLTHROUGH*/
		case 'u':
			_ulong = UARG();
			base = DEC;
			goto nosign;
		case 'X':
			xdigs = "0123456789ABCDEF";
			goto hex;
		case 'x':
			xdigs = "0123456789abcdef";
hex:			_ulong = UARG();
			base = HEX;
			/* leading 0x/X only if non-zero */
			if (flags & ALT && _ulong != 0)
				flags |= HEXPREFIX;

			/* unsigned conversions */
nosign:			sign = '\0';
			/*
			 * ``... diouXx conversions ... if a precision is
			 * specified, the 0 flag will be ignored.''
			 *	-- ANSI X3J11
			 */
number:			if ((dprec = prec) >= 0)
				flags &= ~ZEROPAD;

			/*
			 * ``The result of converting a zero value with an
			 * explicit precision of zero is no characters.''
			 *	-- ANSI X3J11
			 */
			cp = buf + BUF;
			if (_ulong != 0 || prec != 0) {
				/*
				 * unsigned mod is hard, and unsigned mod
				 * by a constant is easier than that by
				 * a variable; hence this switch.
				 */
				switch (base) {
				case OCT:
					do {
						*--cp = to_char(_ulong & 7);
						_ulong >>= 3;
					} while (_ulong);
					/* handle octal leading 0 */
					if (flags & ALT && *cp != '0')
						*--cp = '0';
					break;

				case DEC:
					/* many numbers are 1 digit */
					while (_ulong >= 10) {
						*--cp = to_char(_ulong % 10);
						_ulong /= 10;
					}
					*--cp = to_char(_ulong);
					break;

				case HEX:
					do {
						*--cp = xdigs[_ulong & 15];
						_ulong >>= 4;
					} while (_ulong);
					break;

				default:
					cp = "bug in vfprintf: bad base";
					size = strlen(cp);
					goto skipsize;
				}
			}
			size = buf + BUF - cp;
		skipsize:
			break;
		default:	/* "%?" prints ?, unless ? is NUL */
			if (ch == '\0')
				goto done;
			/* pretend it was %c with argument ch */
			cp = buf;
			*cp = ch;
			size = 1;
			sign = '\0';
			break;
		}

		/*
		 * All reasonable formats wind up here.  At this point,
		 * `cp' points to a string which (if not flags&LADJUST)
		 * should be padded out to `width' places.  If
		 * flags&ZEROPAD, it should first be prefixed by any
		 * sign or other prefix; otherwise, it should be blank
		 * padded before the prefix is emitted.  After any
		 * left-hand padding and prefixing, emit zeroes
		 * required by a decimal [diouxX] precision, then print
		 * the string proper, then emit zeroes required by any
		 * leftover floating precision; finally, if LADJUST,
		 * pad with blanks.
		 */

		/*
		 * compute actual size, so we know how much to pad.
		 * fieldsz excludes decimal prec; realsz includes it
		 */
#ifdef FLOATING_POINT
		fieldsz = size + fpprec;
#else
		fieldsz = size;
#endif
		if (sign)
			fieldsz++;
		else if (flags & HEXPREFIX)
			fieldsz += 2;
		realsz = dprec > fieldsz ? dprec : fieldsz;

		/* right-adjusting blank padding */
		if ((flags & (LADJUST|ZEROPAD)) == 0)
			PAD(width - realsz, blanks);

		/* prefix */
		if (sign) {
			PRINT(&sign, 1);
		} else if (flags & HEXPREFIX) {
			ox[0] = '0';
			ox[1] = ch;
			PRINT(ox, 2);
		}

		/* right-adjusting zero padding */
		if ((flags & (LADJUST|ZEROPAD)) == ZEROPAD)
			PAD(width - realsz, zeroes);

		/* leading zeroes from decimal precision */
		PAD(dprec - fieldsz, zeroes);

		/* the string or number proper */
		PRINT(cp, size);

#ifdef FLOATING_POINT
		/* trailing f.p. zeroes */
		PAD(fpprec, zeroes);
#endif

		/* left-adjusting padding (always blank) */
		if (flags & LADJUST)
			PAD(width - realsz, blanks);

		/* finally, adjust ret */
		ret += width > realsz ? width : realsz;

		FLUSH();	/* copy out the I/O vectors */
	}
done:
	FLUSH();
error:
	return (__sferror(fp) ? EOF : ret);
	/* NOTREACHED */
}

#ifdef FLOATING_POINT
#include <math.h>

static char *exponent();
static char *round();

#if defined(hp300) || defined(sparc)
/*
 * Check for special IEEE format values (NaN, Inf).
 */
static char *
isspecial(d, signp)
	double d;
	char *signp;
{
	register struct IEEEdp {
		unsigned sign:1;
		unsigned exp:11;
		unsigned manh:20;
		unsigned manl:32;
	} *ip = (struct IEEEdp *)&d;

	if (ip->exp != 0x7ff)
		return (NULL);
	if (ip->sign)
		*signp = '-';
	return (ip->manh || ip->manl ? "NaN" : "Inf");
}
#endif /* hp300 or sparc */

static int
cvt(number, prec, flags, signp, fmtch, startp, endp)
	double number;
	register int prec;
	int flags;
	char *signp;
	int fmtch;
	char *startp, *endp;
{
	register char *p, *t;
	register double fract;
	int dotrim, expcnt, gformat;
	double integer, tmp;

	dotrim = expcnt = gformat = 0;
	if (number < 0) {
		number = -number;
		*signp = '-';
	} else
		*signp = 0;

	fract = modf(number, &integer);

	/* get an extra slot for rounding. */
	t = ++startp;

	/*
	 * get integer portion of number; put into the end of the buffer; the
	 * .01 is added for modf(356.0 / 10, &integer) returning .59999999...
	 */
	for (p = endp - 1; integer; ++expcnt) {
		tmp = modf(integer / 10, &integer);
		*p-- = to_char((int)((tmp + .01) * 10));
	}
	switch (fmtch) {
	case 'f':
		/* reverse integer into beginning of buffer */
		if (expcnt)
			for (; ++p < endp; *t++ = *p);
		else
			*t++ = '0';
		/*
		 * if precision required or alternate flag set, add in a
		 * decimal point.
		 */
		if (prec || flags&ALT)
			*t++ = '.';
		/* if requires more precision and some fraction left */
		if (fract) {
			if (prec)
				do {
					fract = modf(fract * 10, &tmp);
					*t++ = to_char((int)tmp);
				} while (--prec && fract);
			if (fract)
				startp = round(fract, (int *)NULL, startp,
				    t - 1, (char)0, signp);
		}
		for (; prec--; *t++ = '0');
		break;
	case 'e':
	case 'E':
eformat:	if (expcnt) {
			*t++ = *++p;
			if (prec || flags&ALT)
				*t++ = '.';
			/* if requires more precision and some integer left */
			for (; prec && ++p < endp; --prec)
				*t++ = *p;
			/*
			 * if done precision and more of the integer component,
			 * round using it; adjust fract so we don't re-round
			 * later.
			 */
			if (!prec && ++p < endp) {
				fract = 0;
				startp = round((double)0, &expcnt, startp,
				    t - 1, *p, signp);
			}
			/* adjust expcnt for digit in front of decimal */
			--expcnt;
		}
		/* until first fractional digit, decrement exponent */
		else if (fract) {
			/* adjust expcnt for digit in front of decimal */
			for (expcnt = -1;; --expcnt) {
				fract = modf(fract * 10, &tmp);
				if (tmp)
					break;
			}
			*t++ = to_char((int)tmp);
			if (prec || flags&ALT)
				*t++ = '.';
		}
		else {
			*t++ = '0';
			if (prec || flags&ALT)
				*t++ = '.';
		}
		/* if requires more precision and some fraction left */
		if (fract) {
			if (prec)
				do {
					fract = modf(fract * 10, &tmp);
					*t++ = to_char((int)tmp);
				} while (--prec && fract);
			if (fract)
				startp = round(fract, &expcnt, startp,
				    t - 1, (char)0, signp);
		}
		/* if requires more precision */
		for (; prec--; *t++ = '0');

		/* unless alternate flag, trim any g/G format trailing 0's */
		if (gformat && !(flags&ALT)) {
			while (t > startp && *--t == '0');
			if (*t == '.')
				--t;
			++t;
		}
		t = exponent(t, expcnt, fmtch);
		break;
	case 'g':
	case 'G':
		/* a precision of 0 is treated as a precision of 1. */
		if (!prec)
			++prec;
		/*
		 * ``The style used depends on the value converted; style e
		 * will be used only if the exponent resulting from the
		 * conversion is less than -4 or greater than the precision.''
		 *	-- ANSI X3J11
		 */
		if (expcnt > prec || !expcnt && fract && fract < .0001) {
			/*
			 * g/G format counts "significant digits, not digits of
			 * precision; for the e/E format, this just causes an
			 * off-by-one problem, i.e. g/G considers the digit
			 * before the decimal point significant and e/E doesn't
			 * count it as precision.
			 */
			--prec;
			fmtch -= 2;		/* G->E, g->e */
			gformat = 1;
			goto eformat;
		}
		/*
		 * reverse integer into beginning of buffer,
		 * note, decrement precision
		 */
		if (expcnt)
			for (; ++p < endp; *t++ = *p, --prec);
		else
			*t++ = '0';
		/*
		 * if precision required or alternate flag set, add in a
		 * decimal point.  If no digits yet, add in leading 0.
		 */
		if (prec || flags&ALT) {
			dotrim = 1;
			*t++ = '.';
		}
		else
			dotrim = 0;
		/* if requires more precision and some fraction left */
		if (fract) {
			if (prec) {
				do {
					fract = modf(fract * 10, &tmp);
					*t++ = to_char((int)tmp);
				} while(!tmp);
				while (--prec && fract) {
					fract = modf(fract * 10, &tmp);
					*t++ = to_char((int)tmp);
				}
			}
			if (fract)
				startp = round(fract, (int *)NULL, startp,
				    t - 1, (char)0, signp);
		}
		/* alternate format, adds 0's for precision, else trim 0's */
		if (flags&ALT)
			for (; prec--; *t++ = '0');
		else if (dotrim) {
			while (t > startp && *--t == '0');
			if (*t != '.')
				++t;
		}
	}
	return (t - startp);
}

static char *
round(fract, exp, start, end, ch, signp)
	double fract;
	int *exp;
	register char *start, *end;
	char ch, *signp;
{
	double tmp;

	if (fract)
		(void)modf(fract * 10, &tmp);
	else
		tmp = to_digit(ch);
	if (tmp > 4)
		for (;; --end) {
			if (*end == '.')
				--end;
			if (++*end <= '9')
				break;
			*end = '0';
			if (end == start) {
				if (exp) {	/* e/E; increment exponent */
					*end = '1';
					++*exp;
				}
				else {		/* f; add extra digit */
				*--end = '1';
				--start;
				}
				break;
			}
		}
	/* ``"%.3f", (double)-0.0004'' gives you a negative 0. */
	else if (*signp == '-')
		for (;; --end) {
			if (*end == '.')
				--end;
			if (*end != '0')
				break;
			if (end == start)
				*signp = 0;
		}
	return (start);
}

static char *
exponent(p, exp, fmtch)
	register char *p;
	register int exp;
	int fmtch;
{
	register char *t;
	char expbuf[MAXEXP];

	*p++ = fmtch;
	if (exp < 0) {
		exp = -exp;
		*p++ = '-';
	}
	else
		*p++ = '+';
	t = expbuf + MAXEXP;
	if (exp > 9) {
		do {
			*--t = to_char(exp % 10);
		} while ((exp /= 10) > 9);
		*--t = to_char(exp);
		for (; t < expbuf + MAXEXP; *p++ = *t++);
	}
	else {
		*p++ = '0';
		*p++ = to_char(exp);
	}
	return (p);
}
#endif /* FLOATING_POINT */