lib/libc/gdtoa/_ldtoa.c

   1 /*-
   2  * Copyright (c) 2003 David Schultz <das@FreeBSD.ORG>
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  *
  26  * $FreeBSD: src/lib/libc/gdtoa/_ldtoa.c,v 1.5 2007/12/09 19:48:57 das Exp $
  27  */
  28
  29 #include <float.h>
  30 #include <inttypes.h>
  31 #include <limits.h>
  32 #include <math.h>
  33 #include <stdlib.h>
  34 #include "fpmath.h"
  35 #include "gdtoaimp.h"
  36
  37 /*
  38  * ldtoa() is a wrapper for gdtoa() that makes it smell like dtoa(),
  39  * except that the floating point argument is passed by reference.
  40  * When dtoa() is passed a NaN or infinity, it sets expt to 9999.
  41  * However, a long double could have a valid exponent of 9999, so we
  42  * use INT_MAX in ldtoa() instead.
  43  */
  44 char *
  45 __ldtoa(long double *ld, int mode, int ndigits, int *decpt, int *sign,
  46     char **rve)
  47 {
  48         FPI fpi = {
  49                 LDBL_MANT_DIG,                  /* nbits */
  50                 LDBL_MIN_EXP - LDBL_MANT_DIG,   /* emin */
  51                 LDBL_MAX_EXP - LDBL_MANT_DIG,   /* emax */
  52                 FLT_ROUNDS,                     /* rounding */
  53 #ifdef Sudden_Underflow /* unused, but correct anyway */
  54                 1
  55 #else
  56                 0
  57 #endif
  58         };
  59         int be, kind;
  60         char *ret;
  61         union IEEEl2bits u;
  62         uint32_t bits[(LDBL_MANT_DIG + 31) / 32];
  63         void *vbits = bits;
  64
  65         u.e = *ld;
  66
  67         /*
  68          * gdtoa doesn't know anything about the sign of the number, so
  69          * if the number is negative, we need to swap rounding modes of
  70          * 2 (upwards) and 3 (downwards).
  71          */
  72         *sign = u.bits.sign;
  73         fpi.rounding ^= (fpi.rounding >> 1) & u.bits.sign;
  74
  75         be = u.bits.exp - (LDBL_MAX_EXP - 1) - (LDBL_MANT_DIG - 1);
  76         LDBL_TO_ARRAY32(u, bits);
  77
  78         switch (fpclassify(u.e)) {
  79         case FP_NORMAL:
  80                 kind = STRTOG_Normal;
  81 #ifdef  LDBL_IMPLICIT_NBIT
  82                 bits[LDBL_MANT_DIG / 32] |= 1 << ((LDBL_MANT_DIG - 1) % 32);
  83 #endif /* LDBL_IMPLICIT_NBIT */
  84                 break;
  85         case FP_ZERO:
  86                 kind = STRTOG_Zero;
  87                 break;
  88         case FP_SUBNORMAL:
  89                 kind = STRTOG_Denormal;
  90                 be++;
  91                 break;
  92         case FP_INFINITE:
  93                 kind = STRTOG_Infinite;
  94                 break;
  95         case FP_NAN:
  96                 kind = STRTOG_NaN;
  97                 break;
  98         default:
  99                 abort();
 100         }
 101
 102         ret = gdtoa(&fpi, be, vbits, &kind, mode, ndigits, decpt, rve);
 103         if (*decpt == -32768)
 104                 *decpt = INT_MAX;
 105         return ret;
 106 }