snprintf.c

Go to the documentation of this file.

/*
 * Copyright (c) 1983, 1995, 1996 Eric P. Allman
 * Copyright (c) 1988, 1993
 *  The Regents of the University of California.  All rights reserved.
 *
 * 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. 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.
 *
 * src/port/snprintf.c
 */

#include "c.h"

#include <ctype.h>
#ifdef _MSC_VER
#include <float.h>              /* for _isnan */
#endif
#include <limits.h>
#include <math.h>
#ifndef WIN32
#include <sys/ioctl.h>
#endif
#include <sys/param.h>

#ifndef NL_ARGMAX
#define NL_ARGMAX 16
#endif


/*
 *  SNPRINTF, VSNPRINTF and friends
 *
 * These versions have been grabbed off the net.  They have been
 * cleaned up to compile properly and support for most of the Single Unix
 * Specification has been added.  Remaining unimplemented features are:
 *
 * 1. No locale support: the radix character is always '.' and the '
 * (single quote) format flag is ignored.
 *
 * 2. No support for the "%n" format specification.
 *
 * 3. No support for wide characters ("lc" and "ls" formats).
 *
 * 4. No support for "long double" ("Lf" and related formats).
 *
 * 5. Space and '#' flags are not implemented.
 *
 *
 * The result values of these functions are not the same across different
 * platforms.  This implementation is compatible with the Single Unix Spec:
 *
 * 1. -1 is returned only if processing is abandoned due to an invalid
 * parameter, such as incorrect format string.  (Although not required by
 * the spec, this happens only when no characters have yet been transmitted
 * to the destination.)
 *
 * 2. For snprintf and sprintf, 0 is returned if str == NULL or count == 0;
 * no data has been stored.
 *
 * 3. Otherwise, the number of bytes actually transmitted to the destination
 * is returned (excluding the trailing '\0' for snprintf and sprintf).
 *
 * For snprintf with nonzero count, the result cannot be more than count-1
 * (a trailing '\0' is always stored); it is not possible to distinguish
 * buffer overrun from exact fit.  This is unlike some implementations that
 * return the number of bytes that would have been needed for the complete
 * result string.
 */

/**************************************************************
 * Original:
 * Patrick Powell Tue Apr 11 09:48:21 PDT 1995
 * A bombproof version of doprnt (dopr) included.
 * Sigh.  This sort of thing is always nasty do deal with.  Note that
 * the version here does not include floating point. (now it does ... tgl)
 **************************************************************/

/* Prevent recursion */
#undef  vsnprintf
#undef  snprintf
#undef  sprintf
#undef  vfprintf
#undef  fprintf
#undef  printf

/* Info about where the formatted output is going */
typedef struct
{
    char       *bufptr;         /* next buffer output position */
    char       *bufstart;       /* first buffer element */
    char       *bufend;         /* last buffer element, or NULL */
    /* bufend == NULL is for sprintf, where we assume buf is big enough */
    FILE       *stream;         /* eventual output destination, or NULL */
    int         nchars;         /* # chars already sent to stream */
    bool        failed;         /* call is a failure; errno is set */
} PrintfTarget;

/*
 * Info about the type and value of a formatting parameter.  Note that we
 * don't currently support "long double", "wint_t", or "wchar_t *" data,
 * nor the '%n' formatting code; else we'd need more types.  Also, at this
 * level we need not worry about signed vs unsigned values.
 */
typedef enum
{
    ATYPE_NONE = 0,
    ATYPE_INT,
    ATYPE_LONG,
    ATYPE_LONGLONG,
    ATYPE_DOUBLE,
    ATYPE_CHARPTR
} PrintfArgType;

typedef union
{
    int         i;
    long        l;
    int64       ll;
    double      d;
    char       *cptr;
} PrintfArgValue;


static void flushbuffer(PrintfTarget *target);
static void dopr(PrintfTarget *target, const char *format, va_list args);


int
pg_vsnprintf(char *str, size_t count, const char *fmt, va_list args)
{
    PrintfTarget target;

    if (str == NULL || count == 0)
        return 0;
    target.bufstart = target.bufptr = str;
    target.bufend = str + count - 1;
    target.stream = NULL;
    /* target.nchars is unused in this case */
    target.failed = false;
    dopr(&target, fmt, args);
    *(target.bufptr) = '\0';
    return target.failed ? -1 : (target.bufptr - target.bufstart);
}

int
pg_snprintf(char *str, size_t count, const char *fmt,...)
{
    int         len;
    va_list     args;

    va_start(args, fmt);
    len = pg_vsnprintf(str, count, fmt, args);
    va_end(args);
    return len;
}

static int
pg_vsprintf(char *str, const char *fmt, va_list args)
{
    PrintfTarget target;

    if (str == NULL)
        return 0;
    target.bufstart = target.bufptr = str;
    target.bufend = NULL;
    target.stream = NULL;
    /* target.nchars is unused in this case */
    target.failed = false;
    dopr(&target, fmt, args);
    *(target.bufptr) = '\0';
    return target.failed ? -1 : (target.bufptr - target.bufstart);
}

int
pg_sprintf(char *str, const char *fmt,...)
{
    int         len;
    va_list     args;

    va_start(args, fmt);
    len = pg_vsprintf(str, fmt, args);
    va_end(args);
    return len;
}

int
pg_vfprintf(FILE *stream, const char *fmt, va_list args)
{
    PrintfTarget target;
    char        buffer[1024];   /* size is arbitrary */

    if (stream == NULL)
    {
        errno = EINVAL;
        return -1;
    }
    target.bufstart = target.bufptr = buffer;
    target.bufend = buffer + sizeof(buffer) - 1;
    target.stream = stream;
    target.nchars = 0;
    target.failed = false;
    dopr(&target, fmt, args);
    /* dump any remaining buffer contents */
    flushbuffer(&target);
    return target.failed ? -1 : target.nchars;
}

int
pg_fprintf(FILE *stream, const char *fmt,...)
{
    int         len;
    va_list     args;

    va_start(args, fmt);
    len = pg_vfprintf(stream, fmt, args);
    va_end(args);
    return len;
}

int
pg_printf(const char *fmt,...)
{
    int         len;
    va_list     args;

    va_start(args, fmt);
    len = pg_vfprintf(stdout, fmt, args);
    va_end(args);
    return len;
}

/*
 * Attempt to write the entire buffer to target->stream; discard the entire
 * buffer in any case.  Call this only when target->stream is defined.
 */
static void
flushbuffer(PrintfTarget *target)
{
    size_t      nc = target->bufptr - target->bufstart;

    if (!target->failed && nc > 0)
    {
        size_t      written;

        written = fwrite(target->bufstart, 1, nc, target->stream);
        target->nchars += written;
        if (written != nc)
            target->failed = true;
    }
    target->bufptr = target->bufstart;
}


static void fmtstr(char *value, int leftjust, int minlen, int maxwidth,
       int pointflag, PrintfTarget *target);
static void fmtptr(void *value, PrintfTarget *target);
static void fmtint(int64 value, char type, int forcesign,
       int leftjust, int minlen, int zpad, int precision, int pointflag,
       PrintfTarget *target);
static void fmtchar(int value, int leftjust, int minlen, PrintfTarget *target);
static void fmtfloat(double value, char type, int forcesign,
         int leftjust, int minlen, int zpad, int precision, int pointflag,
         PrintfTarget *target);
static void dostr(const char *str, int slen, PrintfTarget *target);
static void dopr_outch(int c, PrintfTarget *target);
static int  adjust_sign(int is_negative, int forcesign, int *signvalue);
static void adjust_padlen(int minlen, int vallen, int leftjust, int *padlen);
static void leading_pad(int zpad, int *signvalue, int *padlen,
            PrintfTarget *target);
static void trailing_pad(int *padlen, PrintfTarget *target);


/*
 * dopr(): poor man's version of doprintf
 */
static void
dopr(PrintfTarget *target, const char *format, va_list args)
{
    const char *format_start = format;
    int         ch;
    bool        have_dollar;
    bool        have_non_dollar;
    bool        have_star;
    bool        afterstar;
    int         accum;
    int         longlongflag;
    int         longflag;
    int         pointflag;
    int         leftjust;
    int         fieldwidth;
    int         precision;
    int         zpad;
    int         forcesign;
    int         last_dollar;
    int         fmtpos;
    int         cvalue;
    int64       numvalue;
    double      fvalue;
    char       *strvalue;
    int         i;
    PrintfArgType argtypes[NL_ARGMAX + 1];
    PrintfArgValue argvalues[NL_ARGMAX + 1];

    /*
     * Parse the format string to determine whether there are %n$ format
     * specs, and identify the types and order of the format parameters.
     */
    have_dollar = have_non_dollar = false;
    last_dollar = 0;
    MemSet(argtypes, 0, sizeof(argtypes));

    while ((ch = *format++) != '\0')
    {
        if (ch != '%')
            continue;
        longflag = longlongflag = pointflag = 0;
        fmtpos = accum = 0;
        afterstar = false;
nextch1:
        ch = *format++;
        if (ch == '\0')
            break;              /* illegal, but we don't complain */
        switch (ch)
        {
            case '-':
            case '+':
                goto nextch1;
            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
                accum = accum * 10 + (ch - '0');
                goto nextch1;
            case '.':
                pointflag = 1;
                accum = 0;
                goto nextch1;
            case '*':
                if (afterstar)
                    have_non_dollar = true; /* multiple stars */
                afterstar = true;
                accum = 0;
                goto nextch1;
            case '$':
                have_dollar = true;
                if (accum <= 0 || accum > NL_ARGMAX)
                    goto bad_format;
                if (afterstar)
                {
                    if (argtypes[accum] &&
                        argtypes[accum] != ATYPE_INT)
                        goto bad_format;
                    argtypes[accum] = ATYPE_INT;
                    last_dollar = Max(last_dollar, accum);
                    afterstar = false;
                }
                else
                    fmtpos = accum;
                accum = 0;
                goto nextch1;
            case 'l':
                if (longflag)
                    longlongflag = 1;
                else
                    longflag = 1;
                goto nextch1;
            case 'z':
#if SIZEOF_SIZE_T == 8
#ifdef HAVE_LONG_INT_64
                longflag = 1;
#elif defined(HAVE_LONG_LONG_INT_64)
                longlongflag = 1;
#else
#error "Don't know how to print 64bit integers"
#endif
#else
                /* assume size_t is same size as int */
#endif
                goto nextch1;
            case 'h':
            case '\'':
                /* ignore these */
                goto nextch1;
            case 'd':
            case 'i':
            case 'o':
            case 'u':
            case 'x':
            case 'X':
                if (fmtpos)
                {
                    PrintfArgType atype;

                    if (longlongflag)
                        atype = ATYPE_LONGLONG;
                    else if (longflag)
                        atype = ATYPE_LONG;
                    else
                        atype = ATYPE_INT;
                    if (argtypes[fmtpos] &&
                        argtypes[fmtpos] != atype)
                        goto bad_format;
                    argtypes[fmtpos] = atype;
                    last_dollar = Max(last_dollar, fmtpos);
                }
                else
                    have_non_dollar = true;
                break;
            case 'c':
                if (fmtpos)
                {
                    if (argtypes[fmtpos] &&
                        argtypes[fmtpos] != ATYPE_INT)
                        goto bad_format;
                    argtypes[fmtpos] = ATYPE_INT;
                    last_dollar = Max(last_dollar, fmtpos);
                }
                else
                    have_non_dollar = true;
                break;
            case 's':
            case 'p':
                if (fmtpos)
                {
                    if (argtypes[fmtpos] &&
                        argtypes[fmtpos] != ATYPE_CHARPTR)
                        goto bad_format;
                    argtypes[fmtpos] = ATYPE_CHARPTR;
                    last_dollar = Max(last_dollar, fmtpos);
                }
                else
                    have_non_dollar = true;
                break;
            case 'e':
            case 'E':
            case 'f':
            case 'g':
            case 'G':
                if (fmtpos)
                {
                    if (argtypes[fmtpos] &&
                        argtypes[fmtpos] != ATYPE_DOUBLE)
                        goto bad_format;
                    argtypes[fmtpos] = ATYPE_DOUBLE;
                    last_dollar = Max(last_dollar, fmtpos);
                }
                else
                    have_non_dollar = true;
                break;
            case '%':
                break;
        }

        /*
         * If we finish the spec with afterstar still set, there's a
         * non-dollar star in there.
         */
        if (afterstar)
            have_non_dollar = true;
    }

    /* Per spec, you use either all dollar or all not. */
    if (have_dollar && have_non_dollar)
        goto bad_format;

    /*
     * In dollar mode, collect the arguments in physical order.
     */
    for (i = 1; i <= last_dollar; i++)
    {
        switch (argtypes[i])
        {
            case ATYPE_NONE:
                goto bad_format;
            case ATYPE_INT:
                argvalues[i].i = va_arg(args, int);
                break;
            case ATYPE_LONG:
                argvalues[i].l = va_arg(args, long);
                break;
            case ATYPE_LONGLONG:
                argvalues[i].ll = va_arg(args, int64);
                break;
            case ATYPE_DOUBLE:
                argvalues[i].d = va_arg(args, double);
                break;
            case ATYPE_CHARPTR:
                argvalues[i].cptr = va_arg(args, char *);
                break;
        }
    }

    /*
     * At last we can parse the format for real.
     */
    format = format_start;
    while ((ch = *format++) != '\0')
    {
        if (target->failed)
            break;

        if (ch != '%')
        {
            dopr_outch(ch, target);
            continue;
        }
        fieldwidth = precision = zpad = leftjust = forcesign = 0;
        longflag = longlongflag = pointflag = 0;
        fmtpos = accum = 0;
        have_star = afterstar = false;
nextch2:
        ch = *format++;
        if (ch == '\0')
            break;              /* illegal, but we don't complain */
        switch (ch)
        {
            case '-':
                leftjust = 1;
                goto nextch2;
            case '+':
                forcesign = 1;
                goto nextch2;
            case '0':
                /* set zero padding if no nonzero digits yet */
                if (accum == 0 && !pointflag)
                    zpad = '0';
                /* FALL THRU */
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
                accum = accum * 10 + (ch - '0');
                goto nextch2;
            case '.':
                if (have_star)
                    have_star = false;
                else
                    fieldwidth = accum;
                pointflag = 1;
                accum = 0;
                goto nextch2;
            case '*':
                if (have_dollar)
                {
                    /* process value after reading n$ */
                    afterstar = true;
                }
                else
                {
                    /* fetch and process value now */
                    int         starval = va_arg(args, int);

                    if (pointflag)
                    {
                        precision = starval;
                        if (precision < 0)
                        {
                            precision = 0;
                            pointflag = 0;
                        }
                    }
                    else
                    {
                        fieldwidth = starval;
                        if (fieldwidth < 0)
                        {
                            leftjust = 1;
                            fieldwidth = -fieldwidth;
                        }
                    }
                }
                have_star = true;
                accum = 0;
                goto nextch2;
            case '$':
                if (afterstar)
                {
                    /* fetch and process star value */
                    int         starval = argvalues[accum].i;

                    if (pointflag)
                    {
                        precision = starval;
                        if (precision < 0)
                        {
                            precision = 0;
                            pointflag = 0;
                        }
                    }
                    else
                    {
                        fieldwidth = starval;
                        if (fieldwidth < 0)
                        {
                            leftjust = 1;
                            fieldwidth = -fieldwidth;
                        }
                    }
                    afterstar = false;
                }
                else
                    fmtpos = accum;
                accum = 0;
                goto nextch2;
            case 'l':
                if (longflag)
                    longlongflag = 1;
                else
                    longflag = 1;
                goto nextch2;
            case 'z':
#if SIZEOF_SIZE_T == 8
#ifdef HAVE_LONG_INT_64
                longflag = 1;
#elif defined(HAVE_LONG_LONG_INT_64)
                longlongflag = 1;
#else
#error "Don't know how to print 64bit integers"
#endif
#else
                /* assume size_t is same size as int */
#endif
                goto nextch2;
            case 'h':
            case '\'':
                /* ignore these */
                goto nextch2;
            case 'd':
            case 'i':
                if (!have_star)
                {
                    if (pointflag)
                        precision = accum;
                    else
                        fieldwidth = accum;
                }
                if (have_dollar)
                {
                    if (longlongflag)
                        numvalue = argvalues[fmtpos].ll;
                    else if (longflag)
                        numvalue = argvalues[fmtpos].l;
                    else
                        numvalue = argvalues[fmtpos].i;
                }
                else
                {
                    if (longlongflag)
                        numvalue = va_arg(args, int64);
                    else if (longflag)
                        numvalue = va_arg(args, long);
                    else
                        numvalue = va_arg(args, int);
                }
                fmtint(numvalue, ch, forcesign, leftjust, fieldwidth, zpad,
                       precision, pointflag, target);
                break;
            case 'o':
            case 'u':
            case 'x':
            case 'X':
                if (!have_star)
                {
                    if (pointflag)
                        precision = accum;
                    else
                        fieldwidth = accum;
                }
                if (have_dollar)
                {
                    if (longlongflag)
                        numvalue = (uint64) argvalues[fmtpos].ll;
                    else if (longflag)
                        numvalue = (unsigned long) argvalues[fmtpos].l;
                    else
                        numvalue = (unsigned int) argvalues[fmtpos].i;
                }
                else
                {
                    if (longlongflag)
                        numvalue = (uint64) va_arg(args, int64);
                    else if (longflag)
                        numvalue = (unsigned long) va_arg(args, long);
                    else
                        numvalue = (unsigned int) va_arg(args, int);
                }
                fmtint(numvalue, ch, forcesign, leftjust, fieldwidth, zpad,
                       precision, pointflag, target);
                break;
            case 'c':
                if (!have_star)
                {
                    if (pointflag)
                        precision = accum;
                    else
                        fieldwidth = accum;
                }
                if (have_dollar)
                    cvalue = (unsigned char) argvalues[fmtpos].i;
                else
                    cvalue = (unsigned char) va_arg(args, int);
                fmtchar(cvalue, leftjust, fieldwidth, target);
                break;
            case 's':
                if (!have_star)
                {
                    if (pointflag)
                        precision = accum;
                    else
                        fieldwidth = accum;
                }
                if (have_dollar)
                    strvalue = argvalues[fmtpos].cptr;
                else
                    strvalue = va_arg(args, char *);
                fmtstr(strvalue, leftjust, fieldwidth, precision, pointflag,
                       target);
                break;
            case 'p':
                /* fieldwidth/leftjust are ignored ... */
                if (have_dollar)
                    strvalue = argvalues[fmtpos].cptr;
                else
                    strvalue = va_arg(args, char *);
                fmtptr((void *) strvalue, target);
                break;
            case 'e':
            case 'E':
            case 'f':
            case 'g':
            case 'G':
                if (!have_star)
                {
                    if (pointflag)
                        precision = accum;
                    else
                        fieldwidth = accum;
                }
                if (have_dollar)
                    fvalue = argvalues[fmtpos].d;
                else
                    fvalue = va_arg(args, double);
                fmtfloat(fvalue, ch, forcesign, leftjust,
                         fieldwidth, zpad,
                         precision, pointflag,
                         target);
                break;
            case '%':
                dopr_outch('%', target);
                break;
        }
    }

    return;

bad_format:
    errno = EINVAL;
    target->failed = true;
}

static size_t
pg_strnlen(const char *str, size_t maxlen)
{
    const char *p = str;

    while (maxlen-- > 0 && *p)
        p++;
    return p - str;
}

static void
fmtstr(char *value, int leftjust, int minlen, int maxwidth,
       int pointflag, PrintfTarget *target)
{
    int         padlen,
                vallen;         /* amount to pad */

    /*
     * If a maxwidth (precision) is specified, we must not fetch more bytes
     * than that.
     */
    if (pointflag)
        vallen = pg_strnlen(value, maxwidth);
    else
        vallen = strlen(value);

    adjust_padlen(minlen, vallen, leftjust, &padlen);

    while (padlen > 0)
    {
        dopr_outch(' ', target);
        --padlen;
    }

    dostr(value, vallen, target);

    trailing_pad(&padlen, target);
}

static void
fmtptr(void *value, PrintfTarget *target)
{
    int         vallen;
    char        convert[64];

    /* we rely on regular C library's sprintf to do the basic conversion */
    vallen = sprintf(convert, "%p", value);
    if (vallen < 0)
        target->failed = true;
    else
        dostr(convert, vallen, target);
}

static void
fmtint(int64 value, char type, int forcesign, int leftjust,
       int minlen, int zpad, int precision, int pointflag,
       PrintfTarget *target)
{
    uint64      base;
    int         dosign;
    const char *cvt = "0123456789abcdef";
    int         signvalue = 0;
    char        convert[64];
    int         vallen = 0;
    int         padlen = 0;     /* amount to pad */
    int         zeropad;        /* extra leading zeroes */

    switch (type)
    {
        case 'd':
        case 'i':
            base = 10;
            dosign = 1;
            break;
        case 'o':
            base = 8;
            dosign = 0;
            break;
        case 'u':
            base = 10;
            dosign = 0;
            break;
        case 'x':
            base = 16;
            dosign = 0;
            break;
        case 'X':
            cvt = "0123456789ABCDEF";
            base = 16;
            dosign = 0;
            break;
        default:
            return;             /* keep compiler quiet */
    }

    /* Handle +/- */
    if (dosign && adjust_sign((value < 0), forcesign, &signvalue))
        value = -value;

    /*
     * SUS: the result of converting 0 with an explicit precision of 0 is no
     * characters
     */
    if (value == 0 && pointflag && precision == 0)
        vallen = 0;
    else
    {
        /* make integer string */
        uint64      uvalue = (uint64) value;

        do
        {
            convert[vallen++] = cvt[uvalue % base];
            uvalue = uvalue / base;
        } while (uvalue);
    }

    zeropad = Max(0, precision - vallen);

    adjust_padlen(minlen, vallen + zeropad, leftjust, &padlen);

    leading_pad(zpad, &signvalue, &padlen, target);

    while (zeropad-- > 0)
        dopr_outch('0', target);

    while (vallen > 0)
        dopr_outch(convert[--vallen], target);

    trailing_pad(&padlen, target);
}

static void
fmtchar(int value, int leftjust, int minlen, PrintfTarget *target)
{
    int         padlen = 0;     /* amount to pad */

    adjust_padlen(minlen, 1, leftjust, &padlen);

    while (padlen > 0)
    {
        dopr_outch(' ', target);
        --padlen;
    }

    dopr_outch(value, target);

    trailing_pad(&padlen, target);
}

static void
fmtfloat(double value, char type, int forcesign, int leftjust,
         int minlen, int zpad, int precision, int pointflag,
         PrintfTarget *target)
{
    int         signvalue = 0;
    int         prec;
    int         vallen;
    char        fmt[32];
    char        convert[1024];
    int         zeropadlen = 0; /* amount to pad with zeroes */
    int         padlen = 0;     /* amount to pad with spaces */

    /*
     * We rely on the regular C library's sprintf to do the basic conversion,
     * then handle padding considerations here.
     *
     * The dynamic range of "double" is about 1E+-308 for IEEE math, and not
     * too wildly more than that with other hardware.  In "f" format, sprintf
     * could therefore generate at most 308 characters to the left of the
     * decimal point; while we need to allow the precision to get as high as
     * 308+17 to ensure that we don't truncate significant digits from very
     * small values.  To handle both these extremes, we use a buffer of 1024
     * bytes and limit requested precision to 350 digits; this should prevent
     * buffer overrun even with non-IEEE math.  If the original precision
     * request was more than 350, separately pad with zeroes.
     */
    if (precision < 0)          /* cover possible overflow of "accum" */
        precision = 0;
    prec = Min(precision, 350);

    if (pointflag)
    {
        if (sprintf(fmt, "%%.%d%c", prec, type) < 0)
            goto fail;
        zeropadlen = precision - prec;
    }
    else if (sprintf(fmt, "%%%c", type) < 0)
        goto fail;

    if (!isnan(value) && adjust_sign((value < 0), forcesign, &signvalue))
        value = -value;

    vallen = sprintf(convert, fmt, value);
    if (vallen < 0)
        goto fail;

    /* If it's infinity or NaN, forget about doing any zero-padding */
    if (zeropadlen > 0 && !isdigit((unsigned char) convert[vallen - 1]))
        zeropadlen = 0;

    adjust_padlen(minlen, vallen + zeropadlen, leftjust, &padlen);

    leading_pad(zpad, &signvalue, &padlen, target);

    if (zeropadlen > 0)
    {
        /* If 'e' or 'E' format, inject zeroes before the exponent */
        char       *epos = strrchr(convert, 'e');

        if (!epos)
            epos = strrchr(convert, 'E');
        if (epos)
        {
            /* pad after exponent */
            dostr(convert, epos - convert, target);
            while (zeropadlen-- > 0)
                dopr_outch('0', target);
            dostr(epos, vallen - (epos - convert), target);
        }
        else
        {
            /* no exponent, pad after the digits */
            dostr(convert, vallen, target);
            while (zeropadlen-- > 0)
                dopr_outch('0', target);
        }
    }
    else
    {
        /* no zero padding, just emit the number as-is */
        dostr(convert, vallen, target);
    }

    trailing_pad(&padlen, target);
    return;

fail:
    target->failed = true;
}

static void
dostr(const char *str, int slen, PrintfTarget *target)
{
    while (slen > 0)
    {
        int         avail;

        if (target->bufend != NULL)
            avail = target->bufend - target->bufptr;
        else
            avail = slen;
        if (avail <= 0)
        {
            /* buffer full, can we dump to stream? */
            if (target->stream == NULL)
                return;         /* no, lose the data */
            flushbuffer(target);
            continue;
        }
        avail = Min(avail, slen);
        memmove(target->bufptr, str, avail);
        target->bufptr += avail;
        str += avail;
        slen -= avail;
    }
}

static void
dopr_outch(int c, PrintfTarget *target)
{
    if (target->bufend != NULL && target->bufptr >= target->bufend)
    {
        /* buffer full, can we dump to stream? */
        if (target->stream == NULL)
            return;             /* no, lose the data */
        flushbuffer(target);
    }
    *(target->bufptr++) = c;
}


static int
adjust_sign(int is_negative, int forcesign, int *signvalue)
{
    if (is_negative)
    {
        *signvalue = '-';
        return true;
    }
    else if (forcesign)
        *signvalue = '+';
    return false;
}


static void
adjust_padlen(int minlen, int vallen, int leftjust, int *padlen)
{
    *padlen = minlen - vallen;
    if (*padlen < 0)
        *padlen = 0;
    if (leftjust)
        *padlen = -(*padlen);
}


static void
leading_pad(int zpad, int *signvalue, int *padlen, PrintfTarget *target)
{
    if (*padlen > 0 && zpad)
    {
        if (*signvalue)
        {
            dopr_outch(*signvalue, target);
            --(*padlen);
            *signvalue = 0;
        }
        while (*padlen > 0)
        {
            dopr_outch(zpad, target);
            --(*padlen);
        }
    }
    while (*padlen > (*signvalue != 0))
    {
        dopr_outch(' ', target);
        --(*padlen);
    }
    if (*signvalue)
    {
        dopr_outch(*signvalue, target);
        if (*padlen > 0)
            --(*padlen);
        else if (*padlen < 0)
            ++(*padlen);
    }
}


static void
trailing_pad(int *padlen, PrintfTarget *target)
{
    while (*padlen < 0)
    {
        dopr_outch(' ', target);
        ++(*padlen);
    }
}