xref: /src/lib/libc/stdio/vfprintf.c

/*	$NetBSD: vfprintf.c,v 1.41 2001/12/02 20:12:03 kleink Exp $	*/

/*-
 * 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.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static char *sccsid = "@(#)vfprintf.c	5.50 (Berkeley) 12/16/92";
#else
__RCSID("$NetBSD: vfprintf.c,v 1.41 2001/12/02 20:12:03 kleink Exp $");
#endif
#endif /* LIBC_SCCS and not lint */

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

#include "namespace.h"
#include <sys/types.h>

#include <assert.h>
#include <errno.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <wchar.h>

#if __STDC__
#include <stdarg.h>
#else
#include <varargs.h>
#endif

#include "local.h"
#include "fvwrite.h"
#include "extern.h"
#include "reentrant.h"

static int __sprint __P((FILE *, struct __suio *));
static int __sbprintf __P((FILE *, const char *, va_list))
     __attribute__((__format__(__printf__, 2, 0)));

/*
 * 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;
	struct __suio *uio;
{
	int err;

	_DIAGASSERT(fp != NULL);
	_DIAGASSERT(uio != NULL);

	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)
	FILE *fp;
	const char *fmt;
	va_list ap;
{
	int ret;
	FILE fake;
	unsigned char buf[BUFSIZ];

	_DIAGASSERT(fp != NULL);
	_DIAGASSERT(fmt != NULL);

	/* 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 = -1;
	if (fake._flags & __SERR)
		fp->_flags |= __SERR;
	return (ret);
}


#ifdef FLOATING_POINT
#include <locale.h>
#include <math.h>
#include "floatio.h"

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

static char *cvt __P((double, int, int, char *, int *, int, int *));
static int exponent __P((char *, int, int));

#else /* no FLOATING_POINT */

#define	BUF		40

#endif /* FLOATING_POINT */

#ifdef lint
static __inline void *__UNCONST __P((const void *));
static __inline void *
__UNCONST(v)
	const void *v;
{
	/* LINTED */
	return (void *) v;
}
#else
#define __UNCONST(v)	(void *)(v)
#endif

/*
 * 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)	((char)((n) + '0'))

/*
 * Flags used during conversion.
 */
#define	ALT		0x001		/* alternate form */
#define	HEXPREFIX	0x002		/* add 0x or 0X prefix */
#define	LADJUST		0x004		/* left adjustment */
#define	LONGDBL		0x008		/* long double; unimplemented */
#define	LONGINT		0x010		/* long integer */
#define	QUADINT		0x020		/* quad integer */
#define	SHORTINT	0x040		/* short integer */
#define	MAXINT		0x080		/* (unsigned) intmax_t */
#define	PTRINT		0x100		/* (unsigned) ptrdiff_t */
#define	SIZEINT		0x200		/* (signed) size_t */
#define	ZEROPAD		0x400		/* zero (as opposed to blank) pad */
#define FPT		0x800		/* Floating point number */
int
vfprintf(fp, fmt0, ap)
	FILE *fp;
	const char *fmt0;
	_BSD_VA_LIST_ ap;
{
	const char *fmt;/* format string */
	int ch;	/* character from fmt */
	int n, m;	/* handy integers (short term usage) */
	const char *cp;	/* handy char pointer (short term usage) */
	char *bp;	/* handy char pointer (short term usage) */
	struct __siov *iovp;/* for PRINT macro */
	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) */
	wchar_t wc;
	mbstate_t ps;
#ifdef FLOATING_POINT
	char *decimal_point = localeconv()->decimal_point;
	char softsign;		/* temporary negative sign for floats */
	double _double = 0;	/* double precision arguments %[eEfgG] */
	int expt;		/* integer value of exponent */
	int expsize = 0;	/* character count for expstr */
	int ndig;		/* actual number of digits returned by cvt */
	char expstr[7];		/* buffer for exponent string */
#endif

#ifdef __GNUC__			/* gcc has builtin quad type (long long) SOS */
#define	quad_t	  long long
#define	u_quad_t  unsigned long long
#endif

#define	INTMAX_T	intmax_t
#define	UINTMAX_T	uintmax_t

	UINTMAX_T _uintmax;	/* integer arguments %[diouxX] */
	enum { OCT, DEC, HEX } base;/* base for [diouxX] conversion */
	int dprec;		/* a copy of prec if [diouxX], 0 otherwise */
	int realsz;		/* field size expanded by dprec */
	int size;		/* size of converted field or string */
	char *xdigs = NULL;	/* 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 const char blanks[PADSIZE] =
	 {' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' '};
	static const 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 = __UNCONST(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&MAXINT ? va_arg(ap, intmax_t) : \
	    flags&PTRINT ? va_arg(ap, ptrdiff_t) : \
	    flags&SIZEINT ? va_arg(ap, ssize_t) : /* XXX */ \
	    flags&QUADINT ? va_arg(ap, quad_t) : \
	    flags&LONGINT ? va_arg(ap, long) : \
	    flags&SHORTINT ? (long)(short)va_arg(ap, int) : \
	    (long)va_arg(ap, int))
#define	UARG() \
	(flags&MAXINT ? va_arg(ap, uintmax_t) : \
	    flags&PTRINT ? va_arg(ap, uintptr_t) : /* XXX */ \
	    flags&SIZEINT ? va_arg(ap, size_t) : \
	    flags&QUADINT ? va_arg(ap, u_quad_t) : \
	    flags&LONGINT ? va_arg(ap, u_long) : \
	    flags&SHORTINT ? (u_long)(u_short)va_arg(ap, int) : \
	    (u_long)va_arg(ap, u_int))

	_DIAGASSERT(fp != NULL);
	_DIAGASSERT(fmt0 != NULL);

	FLOCKFILE(fp);

	/* sorry, fprintf(read_only_file, "") returns -1, not 0 */
	if (cantwrite(fp)) {
		errno = EBADF;
		FUNLOCKFILE(fp);
		return (-1);
	}

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

	fmt = fmt0;
	uio.uio_iov = iovp = iov;
	uio.uio_resid = 0;
	uio.uio_iovcnt = 0;
	ret = 0;

	memset(&ps, 0, sizeof(ps));

	/*
	 * Scan the format for conversions (`%' character).
	 */
	for (;;) {
		cp = fmt;
		while ((n = mbrtowc(&wc, fmt, MB_CUR_MAX, &ps)) > 0) {
			fmt += n;
			if (wc == '%') {
				fmt--;
				break;
			}
		}
		if ((m = fmt - cp) != 0) {
			PRINT(cp, m);
			ret += m;
		}
		if (n <= 0)
			goto done;
		fmt++;		/* skip over '%' */

		flags = 0;
		dprec = 0;
		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 'j':
			flags |= MAXINT;
			goto rflag;
		case 'l':
			if (*fmt == 'l') {
				fmt++;
				flags |= QUADINT;
			} else {
				flags |= LONGINT;
			}
			goto rflag;
		case 'q':
			flags |= QUADINT;
			goto rflag;
		case 't':
			flags |= PTRINT;
			goto rflag;
		case 'z':
			flags |= SIZEINT;
			goto rflag;
		case 'c':
			*buf = va_arg(ap, int);
			cp = buf;
			size = 1;
			sign = '\0';
			break;
		case 'D':
			flags |= LONGINT;
			/*FALLTHROUGH*/
		case 'd':
		case 'i':
			_uintmax = SARG();
			if ((intmax_t)_uintmax < 0) {
				_uintmax = -_uintmax;
				sign = '-';
			}
			base = DEC;
			goto number;
#ifdef FLOATING_POINT
		case 'e':
		case 'E':
		case 'f':
		case 'F':
		case 'g':
		case 'G':
			if (prec == -1) {
				prec = DEFPREC;
			} else if ((ch == 'g' || ch == 'G') && prec == 0) {
				prec = 1;
			}

			if (flags & LONGDBL) {
				_double = (double) va_arg(ap, long double);
			} else {
				_double = va_arg(ap, double);
			}

			/* do this before tricky precision changes */
			if (isinf(_double)) {
				if (_double < 0)
					sign = '-';
				if (ch == 'E' || ch == 'F' || ch == 'G')
					cp = "INF";
				else
					cp = "inf";
				size = 3;
				break;
			}
			if (isnan(_double)) {
				if (ch == 'E' || ch == 'F' || ch == 'G')
					cp = "NAN";
				else
					cp = "nan";
				size = 3;
				break;
			}

			flags |= FPT;
			cp = cvt(_double, prec, flags, &softsign,
				&expt, ch, &ndig);
			if (ch == 'g' || ch == 'G') {
				if (expt <= -4 || expt > prec)
					ch = (ch == 'g') ? 'e' : 'E';
				else
					ch = 'g';
			}
			if (ch == 'e' || ch == 'E') {
				--expt;
				expsize = exponent(expstr, expt, ch);
				size = expsize + ndig;
				if (ndig > 1 || flags & ALT)
					++size;
			} else if (ch == 'f' || ch == 'F') {
				if (expt > 0) {
					size = expt;
					if (prec || flags & ALT)
						size += prec + 1;
				} else	/* "0.X" */
					size = prec + 2;
			} else if (expt >= ndig) {	/* fixed g fmt */
				size = expt;
				if (flags & ALT)
					++size;
			} else
				size = ndig + (expt > 0 ?
					1 : 2 - expt);

			if (softsign)
				sign = '-';
			break;
#endif /* FLOATING_POINT */
		case 'n':
			if (flags & MAXINT)
				*va_arg(ap, intmax_t *) = ret;
			else if (flags & PTRINT)
				*va_arg(ap, ptrdiff_t *) = ret;
			else if (flags & SIZEINT)
				*va_arg(ap, ssize_t *) = ret;	/* XXX */
			else if (flags & QUADINT)
				*va_arg(ap, quad_t *) = ret;
			else 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':
			_uintmax = 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 */
			_uintmax = (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, (size_t)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':
			_uintmax = UARG();
			base = DEC;
			goto nosign;
		case 'X':
			xdigs = "0123456789ABCDEF";
			goto hex;
		case 'x':
			xdigs = "0123456789abcdef";
hex:			_uintmax = UARG();
			base = HEX;
			/* leading 0x/X only if non-zero */
			if (flags & ALT && _uintmax != 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
			 */
			bp = buf + BUF;
			if (_uintmax != 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 {
						*--bp = to_char(_uintmax & 7);
						_uintmax >>= 3;
					} while (_uintmax);
					/* handle octal leading 0 */
					if (flags & ALT && *bp != '0')
						*--bp = '0';
					break;

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

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

				default:
					cp = "bug in vfprintf: bad base";
					size = strlen(cp);
					goto skipsize;
				}
			}
			cp = bp;
			size = buf + BUF - bp;
		skipsize:
			break;
		default:	/* "%?" prints ?, unless ? is NUL */
			if (ch == '\0')
				goto done;
			/* pretend it was %c with argument ch */
			*buf = ch;
			cp = buf;
			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.
		 * size excludes decimal prec; realsz includes it.
		 */
		realsz = dprec > size ? dprec : size;
		if (sign)
			realsz++;
		else if (flags & HEXPREFIX)
			realsz+= 2;

		/* 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 - size, zeroes);

		/* the string or number proper */
#ifdef FLOATING_POINT
		if ((flags & FPT) == 0) {
			PRINT(cp, size);
		} else {	/* glue together f_p fragments */
			if (ch >= 'f') {	/* 'f' or 'g' */
				if (_double == 0) {
					/* kludge for __dtoa irregularity */
					PRINT("0", 1);
					if (expt < ndig || (flags & ALT) != 0) {
						PRINT(decimal_point, 1);
						PAD(ndig - 1, zeroes);
					}
				} else if (expt <= 0) {
					PRINT("0", 1);
					PRINT(decimal_point, 1);
					PAD(-expt, zeroes);
					PRINT(cp, ndig);
				} else if (expt >= ndig) {
					PRINT(cp, ndig);
					PAD(expt - ndig, zeroes);
					if (flags & ALT)
						PRINT(".", 1);
				} else {
					PRINT(cp, expt);
					cp += expt;
					PRINT(".", 1);
					PRINT(cp, ndig-expt);
				}
			} else {	/* 'e' or 'E' */
				if (ndig > 1 || flags & ALT) {
					ox[0] = *cp++;
					ox[1] = '.';
					PRINT(ox, 2);
					if (_double) {
						PRINT(cp, ndig-1);
					} else	/* 0.[0..] */
						/* __dtoa irregularity */
						PAD(ndig - 1, zeroes);
				} else	/* XeYYY */
					PRINT(cp, 1);
				PRINT(expstr, expsize);
			}
		}
#else
		PRINT(cp, size);
#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:
	if (__sferror(fp))
		ret = -1;
	FUNLOCKFILE(fp);
	return (ret);
}

#ifdef FLOATING_POINT

static char *
cvt(value, ndigits, flags, sign, decpt, ch, length)
	double value;
	int ndigits, flags, *decpt, ch, *length;
	char *sign;
{
	int mode, dsgn;
	char *digits, *bp, *rve;

	_DIAGASSERT(decpt != NULL);
	_DIAGASSERT(length != NULL);
	_DIAGASSERT(sign != NULL);

	if (ch == 'f') {
		mode = 3;		/* ndigits after the decimal point */
	} else {
		/* To obtain ndigits after the decimal point for the 'e'
		 * and 'E' formats, round to ndigits + 1 significant
		 * figures.
		 */
		if (ch == 'e' || ch == 'E') {
			ndigits++;
		}
		mode = 2;		/* ndigits significant digits */
	}

	digits = __dtoa(value, mode, ndigits, decpt, &dsgn, &rve);
	if (dsgn) {
		value = -value;
		*sign = '-';
	} else
		*sign = '\000';
	if ((ch != 'g' && ch != 'G') || flags & ALT) {	/* Print trailing zeros */
		bp = digits + ndigits;
		if (ch == 'f') {
			if (*digits == '0' && value)
				*decpt = -ndigits + 1;
			bp += *decpt;
		}
		if (value == 0)	/* kludge for __dtoa irregularity */
			rve = bp;
		while (rve < bp)
			*rve++ = '0';
	}
	*length = rve - digits;
	return (digits);
}

static int
exponent(p0, expon, fmtch)
	char *p0;
	int expon, fmtch;
{
	char *p, *t;
	char expbuf[MAXEXP];

	_DIAGASSERT(p0 != NULL);

	p = p0;
	*p++ = fmtch;
	if (expon < 0) {
		expon = -expon;
		*p++ = '-';
	}
	else
		*p++ = '+';
	t = expbuf + MAXEXP;
	if (expon > 9) {
		do {
			*--t = to_char(expon % 10);
		} while ((expon /= 10) > 9);
		*--t = to_char(expon);
		for (; t < expbuf + MAXEXP; *p++ = *t++);
	}
	else {
		*p++ = '0';
		*p++ = to_char(expon);
	}
	return (p - p0);
}
#endif /* FLOATING_POINT */