76303a9735
1. Previously, printing the number 1.0 could produce 0x1p+0, 0x2p-1, 0x4p-2, or 0x8p-3, depending on what happened to be convenient. This meant that printing a value as a double and printing the same value as a long double could produce different (but equivalent) results. The change is to always make the leading digit a 1, unless the number is 0. This solves the aforementioned problem and has several other advantages. 2. Use the FPU to do rounding. This is far simpler and more portable than manipulating the bits, and it fixes an obsure round-to-even bug. It also raises the exceptions now required by IEEE 754R. The drawbacks are that it is usually slightly slower, and it makes printf less effective as a debugging tool when the FPU is hosed (e.g., due to a buggy softfloat implementation). 3. On i386, twiddle the rounding precision so that (2) works properly for long doubles. 4. Make several simplifications that are now possible due to (2). 5. Split __hldtoa() into a separate file. Thanks to remko for access to a sparc64 box for testing.
143 lines
4.4 KiB
C
143 lines
4.4 KiB
C
/*-
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* Copyright (c) 2004-2008 David Schultz <das@FreeBSD.ORG>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <float.h>
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#include <limits.h>
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#include <math.h>
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#include "fpmath.h"
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#include "gdtoaimp.h"
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/* Strings values used by dtoa() */
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#define INFSTR "Infinity"
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#define NANSTR "NaN"
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#define DBL_ADJ (DBL_MAX_EXP - 2)
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#define SIGFIGS ((DBL_MANT_DIG + 3) / 4 + 1)
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static const float one[] = { 1.0f, -1.0f };
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/*
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* This procedure converts a double-precision number in IEEE format
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* into a string of hexadecimal digits and an exponent of 2. Its
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* behavior is bug-for-bug compatible with dtoa() in mode 2, with the
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* following exceptions:
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*
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* - An ndigits < 0 causes it to use as many digits as necessary to
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* represent the number exactly.
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* - The additional xdigs argument should point to either the string
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* "0123456789ABCDEF" or the string "0123456789abcdef", depending on
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* which case is desired.
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* - This routine does not repeat dtoa's mistake of setting decpt
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* to 9999 in the case of an infinity or NaN. INT_MAX is used
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* for this purpose instead.
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*
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* Note that the C99 standard does not specify what the leading digit
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* should be for non-zero numbers. For instance, 0x1.3p3 is the same
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* as 0x2.6p2 is the same as 0x4.cp3. This implementation always makes
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* the leading digit a 1. This ensures that the exponent printed is the
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* actual base-2 exponent, i.e., ilogb(d).
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*
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* Inputs: d, xdigs, ndigits
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* Outputs: decpt, sign, rve
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*/
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char *
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__hdtoa(double d, const char *xdigs, int ndigits, int *decpt, int *sign,
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char **rve)
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{
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union IEEEd2bits u;
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char *s, *s0;
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int bufsize;
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uint32_t manh, manl;
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u.d = d;
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*sign = u.bits.sign;
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switch (fpclassify(d)) {
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case FP_NORMAL:
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*decpt = u.bits.exp - DBL_ADJ;
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break;
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case FP_ZERO:
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*decpt = 1;
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return (nrv_alloc("0", rve, 1));
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case FP_SUBNORMAL:
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u.d *= 0x1p514;
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*decpt = u.bits.exp - (514 + DBL_ADJ);
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break;
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case FP_INFINITE:
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*decpt = INT_MAX;
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return (nrv_alloc(INFSTR, rve, sizeof(INFSTR) - 1));
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default: /* FP_NAN or unrecognized */
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*decpt = INT_MAX;
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return (nrv_alloc(NANSTR, rve, sizeof(NANSTR) - 1));
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}
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/* FP_NORMAL or FP_SUBNORMAL */
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if (ndigits == 0) /* dtoa() compatibility */
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ndigits = 1;
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/*
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* If ndigits < 0, we are expected to auto-size, so we allocate
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* enough space for all the digits.
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*/
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bufsize = (ndigits > 0) ? ndigits : SIGFIGS;
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s0 = rv_alloc(bufsize);
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/* Round to the desired number of digits. */
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if (SIGFIGS > ndigits && ndigits > 0) {
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float redux = one[u.bits.sign];
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int offset = 4 * ndigits + DBL_MAX_EXP - 4 - DBL_MANT_DIG;
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u.bits.exp = offset;
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u.d += redux;
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u.d -= redux;
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*decpt += u.bits.exp - offset;
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}
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manh = u.bits.manh;
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manl = u.bits.manl;
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*s0 = '1';
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for (s = s0 + 1; s < s0 + bufsize; s++) {
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*s = xdigs[(manh >> (DBL_MANH_SIZE - 4)) & 0xf];
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manh = (manh << 4) | (manl >> (DBL_MANL_SIZE - 4));
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manl <<= 4;
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}
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/* If ndigits < 0, we are expected to auto-size the precision. */
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if (ndigits < 0) {
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for (ndigits = SIGFIGS; s0[ndigits - 1] == '0'; ndigits--)
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;
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}
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s = s0 + ndigits;
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*s = '\0';
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if (rve != NULL)
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*rve = s;
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return (s0);
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}
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