110 lines
3.7 KiB
C
110 lines
3.7 KiB
C
/***
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*_fptostr.c - workhorse routine for converting floating point to string
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*
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* Copyright (c) Microsoft Corporation. All rights reserved.
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*
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*Purpose:
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* Workhorse routine for fcvt, ecvt.
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*
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*******************************************************************************/
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#include <cruntime.h>
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#include <string.h>
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#include <stddef.h>
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#include <fltintrn.h>
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#include <internal.h>
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/***
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*errno_t _fptostr(buf, size, digits, pflt) - workhorse floating point conversion
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*
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*Purpose:
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* This is the workhorse routine for fcvt, ecvt. Here is where
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* all the digits are put into a buffer and the rounding is
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* performed and indicators of the decimal point position are set. Note,
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* this must not change the mantissa field of pflt since routines which
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* use this routine rely on this being unchanged.
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*
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*Entry:
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* char *buf - the buffer in which the digits are to be put
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* int digits - the number of digits which are to go into the buffer
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* STRFLT pflt - a pointer to a structure containing information on the
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* floating point value, including a string containing the
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* non-zero significant digits of the mantissa.
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*
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*Exit:
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* Changes the contents of the buffer and also may increment the decpt
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* field of the structure pointer to by the 'pflt' parameter if overflow
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* occurs during rounding (e.g. 9.999999... gets rounded to 10.000...).
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*
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*Exceptions:
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* Input parameters are validated. Refer to the validation section of the function.
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*
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*******************************************************************************/
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errno_t __cdecl _fptostr (
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char *buf,
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size_t sizeInBytes,
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int digits,
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STRFLT pflt
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)
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{
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char *pbuf = buf;
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char *mantissa = pflt->mantissa;
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/* validation section */
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_VALIDATE_RETURN_ERRCODE(buf != NULL, EINVAL);
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_VALIDATE_RETURN_ERRCODE(sizeInBytes > 0, EINVAL);
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buf[0] = '\0';
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/* the buffer will contains ndec decimal digits plus an optional
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* overflow digit for the rounding
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*/
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_VALIDATE_RETURN_ERRCODE(sizeInBytes > (size_t)((digits > 0 ? digits : 0) + 1), ERANGE);
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_VALIDATE_RETURN_ERRCODE(pflt != NULL, EINVAL);
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/* initialize the first digit in the buffer to '0' (NOTE - NOT '\0')
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* and set the pointer to the second digit of the buffer. The first
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* digit is used to handle overflow on rounding (e.g. 9.9999...
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* becomes 10.000...) which requires a carry into the first digit.
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*/
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*pbuf++ = '0';
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/* Copy the digits of the value into the buffer (with 0 padding)
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* and insert the terminating null character.
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*/
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while (digits > 0) {
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*pbuf++ = (*mantissa) ? *mantissa++ : (char)'0';
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digits--;
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}
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*pbuf = '\0';
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/* do any rounding which may be needed. Note - if digits < 0 don't
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* do any rounding since in this case, the rounding occurs in a digit
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* which will not be output beause of the precision requested
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*/
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if (digits >= 0 && *mantissa >= '5') {
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pbuf--;
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while (*pbuf == '9')
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*pbuf-- = '0';
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*pbuf += 1;
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}
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if (*buf == '1') {
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/* the rounding caused overflow into the leading digit (e.g.
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* 9.999.. went to 10.000...), so increment the decpt position
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* by 1
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*/
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pflt->decpt++;
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}
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else {
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/* move the entire string to the left one digit to remove the
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* unused overflow digit.
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*/
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memmove(buf, buf+1, strlen(buf+1)+1);
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}
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return 0;
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}
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