2 * Copyright (c) 2004-2008 David Schultz <das@FreeBSD.ORG>
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
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12 * documentation and/or other materials provided with the distribution.
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17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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26 * $FreeBSD: src/lib/libc/gdtoa/_hdtoa.c,v 1.7 2008/04/12 14:53:52 das Exp $
33 #include "../stdio/floatio.h"
37 /* Strings values used by dtoa() */
38 #define INFSTR "Infinity"
41 #define DBL_ADJ (DBL_MAX_EXP - 2)
42 #define SIGFIGS ((DBL_MANT_DIG + 3) / 4 + 1)
44 static const float one[] = { 1.0f, -1.0f };
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:
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.
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).
67 * Inputs: d, xdigs, ndigits
68 * Outputs: decpt, sign, rve
71 __hdtoa(double d, const char *xdigs, int ndigits, int *decpt, int *sign,
82 switch (fpclassify(d)) {
84 *decpt = u.bits.exp - DBL_ADJ;
88 return (nrv_alloc("0", rve, 1));
91 *decpt = u.bits.exp - (514 + DBL_ADJ);
95 return (nrv_alloc(INFSTR, rve, sizeof(INFSTR) - 1));
96 default: /* FP_NAN or unrecognized */
98 return (nrv_alloc(NANSTR, rve, sizeof(NANSTR) - 1));
101 /* FP_NORMAL or FP_SUBNORMAL */
103 if (ndigits == 0) /* dtoa() compatibility */
107 * If ndigits < 0, we are expected to auto-size, so we allocate
108 * enough space for all the digits.
110 bufsize = (ndigits > 0) ? ndigits : SIGFIGS;
111 s0 = rv_alloc(bufsize);
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;
120 *decpt += u.bits.exp - offset;
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));
132 /* If ndigits < 0, we are expected to auto-size the precision. */
134 for (ndigits = SIGFIGS; s0[ndigits - 1] == '0'; ndigits--)