fcvt.c

C标准库源代码

/***
*fcvt.c - convert floating point value to string
*
*       Copyright (c) 1985-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       Converts a floating point value to a string.
*
*******************************************************************************/

#include <cruntime.h>
#include <fltintrn.h>
#include <cvt.h>
#include <mtdll.h>
#include <stdlib.h>
#include <dbgint.h>

/*
 * The static character array buf[CVTBUFSIZE] is used by the _fpcvt routine
 * (the workhorse for _ecvt and _fcvt) for storage of its output.  The routine
 * gcvt expects the user to have set up their own storage.  CVTBUFSIZE is set
 * large enough to accomodate the largest double precision number plus 40
 * decimal places (even though you only have 16 digits of accuracy in a
 * double precision IEEE number, the user may ask for more to effect 0
 * padding; but there has to be a limit somewhere).
 */

/*
 * define a maximum size for the conversion buffer.  It should be at least
 * as long as the number of digits in the largest double precision value
 * (?.?e308 in IEEE arithmetic).  We will use the same size buffer as is
 * used in the printf support routine (_output)
 */

#ifdef _MT
char * __cdecl _fpcvt(STRFLT, int, int *, int *);
#else  /* _MT */
static char * __cdecl _fpcvt(STRFLT, int, int *, int *);
static char buf[CVTBUFSIZE];
#endif  /* _MT */

/***
*char *_fcvt(value, ndec, decpr, sign) - convert floating point to char string
*
*Purpose:
*       _fcvt like _ecvt converts the value to a null terminated
*       string of ASCII digits, and returns a pointer to the
*       result.  The routine prepares data for Fortran F-format
*       output with the number of digits following the decimal
*       point specified by ndec.  The position of the decimal
*       point relative to the beginning of the string is returned
*       indirectly through decpt.  The correct digit for Fortran
*       F-format is rounded.
*       NOTE - to avoid the possibility of generating floating
*       point instructions in this code we fool the compiler
*       about the type of the 'value' parameter using a struct.
*       This is OK since all we do is pass it off as a
*       parameter.
*
*Entry:
*       double value - number to be converted
*       int ndec - number of digits after decimal point
*
*Exit:
*       returns pointer to the character string representation of value.
*       also, the output is written into the static char array buf.
*       int *decpt - pointer to int with pos. of dec. point
*       int *sign - pointer to int with sign (0 = pos, non-0 = neg)
*
*Exceptions:
*
*******************************************************************************/

char * __cdecl _fcvt (
        double value,
        int ndec,
        int *decpt,
        int *sign
        )
{
        REG1 STRFLT pflt;

#ifdef _MT
        struct _strflt strfltstruct;
        char resultstring[21];

        /* ok to take address of stack struct here; fltout2 knows to use ss */
        pflt = _fltout2( value, &strfltstruct, resultstring );


#else  /* _MT */
        pflt = _fltout( value );
#endif  /* _MT */

        return( _fpcvt( pflt, pflt->decpt + ndec, decpt, sign ) );
}


/***
*char *_ecvt( value, ndigit, decpt, sign ) - convert floating point to string
*
*Purpose:
*       _ecvt converts value to a null terminated string of
*       ASCII digits, and returns a pointer to the result.
*       The position of the decimal point relative to the
*       begining of the string is stored indirectly through
*       decpt, where negative means to the left of the returned
*       digits.  If the sign of the result is negative, the
*       word pointed to by sign is non zero, otherwise it is
*       zero.  The low order digit is rounded.
*
*Entry:
*       double value - number to be converted
*       int ndigit - number of digits after decimal point
*
*Exit:
*       returns pointer to the character representation of value.
*       also the output is written into the statuc char array buf.
*       int *decpt - pointer to int with position of decimal point
*       int *sign - pointer to int with sign in it (0 = pos, non-0 = neg)
*
*Exceptions:
*
*******************************************************************************/

char * __cdecl _ecvt (
        double value,
        int ndigit,
        int *decpt,
        int *sign
        )
{

        char *retbuf;

#ifdef _MT
        REG1 STRFLT pflt;

        struct _strflt strfltstruct;        /* temporary buffers */
        char resultstring[21];

        /* ok to take address of stack struct here; fltout2 knows to use ss */
        pflt = _fltout2( value, &strfltstruct, resultstring );

        retbuf = _fpcvt( pflt, ndigit, decpt, sign );

#else  /* _MT */
        retbuf = _fpcvt( _fltout(value), ndigit, decpt, sign );
#endif  /* _MT */

        /* _fptostr() occasionally returns an extra character in the buffer ... */

        if (retbuf[ndigit])
                retbuf[ndigit] = '\0';
        return( retbuf );
}


/***
*char *_fpcvt() - gets final string and sets decpt and sign     [STATIC]
*
*Purpose:
*       This is a small common routine used by [ef]cvt.  It calls fptostr
*       to get the final string and sets the decpt and sign indicators.
*
*Entry:
*
*Exit:
*
*Exceptions:
*
*******************************************************************************/

#ifdef _MT
char * __cdecl _fpcvt (
#else  /* _MT */
static char * __cdecl _fpcvt (
#endif  /* _MT */
        REG2 STRFLT pflt,
        REG3 int digits,
        int *decpt,
        int *sign
        )
{

#ifdef _MT

        /* use a per-thread buffer */

        char *buf;

        _ptiddata ptd;

        ptd = _getptd();
        if ( ptd->_cvtbuf == NULL )
                if ( (ptd->_cvtbuf = _malloc_crt(CVTBUFSIZE)) == NULL )
                        return(NULL);
        buf = ptd->_cvtbuf;

#endif  /* _MT */


        /* make sure we don't overflow the buffer size.  If the user asks for
         * more digits than the buffer can handle, truncate it to the maximum
         * size allowed in the buffer.  The maximum size is CVTBUFSIZE - 2
         * since we useone character for overflow and one for the terminating
         * null character.
         */

        _fptostr(buf, (digits > CVTBUFSIZE - 2) ? CVTBUFSIZE - 2 : digits, pflt);

        /* set the sign flag and decimal point position */

        *sign = (pflt->sign == '-') ? 1 : 0;
        *decpt = pflt->decpt;
        return(buf);
}