lib/libc/gdtoa/_hdtoa.c

   1 /*-
   2  * Copyright (c) 2004-2008 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/_hdtoa.c,v 1.7 2008/04/12 14:53:52 das Exp $
  27  */
  28
  29 #include <float.h>
  30 #include <limits.h>
  31 #include <math.h>
  32
  33 #include "../stdio/floatio.h"
  34 #include "fpmath.h"
  35 #include "gdtoaimp.h"
  36
  37 /* Strings values used by dtoa() */
  38 #define INFSTR  "Infinity"
  39 #define NANSTR  "NaN"
  40
  41 #define DBL_ADJ (DBL_MAX_EXP - 2)
  42 #define SIGFIGS ((DBL_MANT_DIG + 3) / 4 + 1)
  43
  44 static const float one[] = { 1.0f, -1.0f };
  45
  46 /*
  47  * This procedure converts a double-precision number in IEEE format
  48  * into a string of hexadecimal digits and an exponent of 2.  Its
  49  * behavior is bug-for-bug compatible with dtoa() in mode 2, with the
  50  * following exceptions:
  51  *
  52  * - An ndigits < 0 causes it to use as many digits as necessary to
  53  *   represent the number exactly.
  54  * - The additional xdigs argument should point to either the string
  55  *   "0123456789ABCDEF" or the string "0123456789abcdef", depending on
  56  *   which case is desired.
  57  * - This routine does not repeat dtoa's mistake of setting decpt
  58  *   to 9999 in the case of an infinity or NaN.  INT_MAX is used
  59  *   for this purpose instead.
  60  *
  61  * Note that the C99 standard does not specify what the leading digit
  62  * should be for non-zero numbers.  For instance, 0x1.3p3 is the same
  63  * as 0x2.6p2 is the same as 0x4.cp3.  This implementation always makes
  64  * the leading digit a 1. This ensures that the exponent printed is the
  65  * actual base-2 exponent, i.e., ilogb(d).
  66  *
  67  * Inputs:      d, xdigs, ndigits
  68  * Outputs:     decpt, sign, rve
  69  */
  70 char *
  71 __hdtoa(double d, const char *xdigs, int ndigits, int *decpt, int *sign,
  72     char **rve)
  73 {
  74         union IEEEd2bits u;
  75         char *s, *s0;
  76         int bufsize;
  77         uint32_t manh, manl;
  78
  79         u.d = d;
  80         *sign = u.bits.sign;
  81
  82         switch (fpclassify(d)) {
  83         case FP_NORMAL:
  84                 *decpt = u.bits.exp - DBL_ADJ;
  85                 break;
  86         case FP_ZERO:
  87                 *decpt = 1;
  88                 return (nrv_alloc("0", rve, 1));
  89         case FP_SUBNORMAL:
  90                 u.d *= 0x1p514;
  91                 *decpt = u.bits.exp - (514 + DBL_ADJ);
  92                 break;
  93         case FP_INFINITE:
  94                 *decpt = INT_MAX;
  95                 return (nrv_alloc(INFSTR, rve, sizeof(INFSTR) - 1));
  96         default:        /* FP_NAN or unrecognized */
  97                 *decpt = INT_MAX;
  98                 return (nrv_alloc(NANSTR, rve, sizeof(NANSTR) - 1));
  99         }
 100
 101         /* FP_NORMAL or FP_SUBNORMAL */
 102
 103         if (ndigits == 0)               /* dtoa() compatibility */
 104                 ndigits = 1;
 105
 106         /*
 107          * If ndigits < 0, we are expected to auto-size, so we allocate
 108          * enough space for all the digits.
 109          */
 110         bufsize = (ndigits > 0) ? ndigits : SIGFIGS;
 111         s0 = rv_alloc(bufsize);
 112
 113         /* Round to the desired number of digits. */
 114         if (SIGFIGS > ndigits && ndigits > 0) {
 115                 float redux = one[u.bits.sign];
 116                 int offset = 4 * ndigits + DBL_MAX_EXP - 4 - DBL_MANT_DIG;
 117                 u.bits.exp = offset;
 118                 u.d += redux;
 119                 u.d -= redux;
 120                 *decpt += u.bits.exp - offset;
 121         }
 122
 123         manh = u.bits.manh;
 124         manl = u.bits.manl;
 125         *s0 = '1';
 126         for (s = s0 + 1; s < s0 + bufsize; s++) {
 127                 *s = xdigs[(manh >> (DBL_MANH_SIZE - 4)) & 0xf];
 128                 manh = (manh << 4) | (manl >> (DBL_MANL_SIZE - 4));
 129                 manl <<= 4;
 130         }
 131
 132         /* If ndigits < 0, we are expected to auto-size the precision. */
 133         if (ndigits < 0) {
 134                 for (ndigits = SIGFIGS; s0[ndigits - 1] == '0'; ndigits--)
 135                         ;
 136         }
 137
 138         s = s0 + ndigits;
 139         *s = '\0';
 140         if (rve != NULL)
 141                 *rve = s;
 142         return (s0);
 143 }