191 lines
5.2 KiB
C
191 lines
5.2 KiB
C
/* Split a double into fraction and mantissa, for hexadecimal printf.
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Copyright (C) 2007, 2009-2022 Free Software Foundation, Inc.
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This file is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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This file is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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#if ! defined USE_LONG_DOUBLE
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# include <config.h>
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#endif
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/* Specification. */
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#ifdef USE_LONG_DOUBLE
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# include "printf-frexpl.h"
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#else
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# include "printf-frexp.h"
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#endif
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#include <float.h>
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#include <math.h>
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#ifdef USE_LONG_DOUBLE
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# include "fpucw.h"
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#endif
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/* This file assumes FLT_RADIX = 2. If FLT_RADIX is a power of 2 greater
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than 2, or not even a power of 2, some rounding errors can occur, so that
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then the returned mantissa is only guaranteed to be <= 2.0, not < 2.0. */
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#ifdef USE_LONG_DOUBLE
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# define FUNC printf_frexpl
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# define DOUBLE long double
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# define MIN_EXP LDBL_MIN_EXP
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# if HAVE_FREXPL_IN_LIBC && HAVE_LDEXPL_IN_LIBC
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# define USE_FREXP_LDEXP
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# define FREXP frexpl
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# define LDEXP ldexpl
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# endif
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# define DECL_ROUNDING DECL_LONG_DOUBLE_ROUNDING
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# define BEGIN_ROUNDING() BEGIN_LONG_DOUBLE_ROUNDING ()
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# define END_ROUNDING() END_LONG_DOUBLE_ROUNDING ()
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# define L_(literal) literal##L
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#else
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# define FUNC printf_frexp
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# define DOUBLE double
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# define MIN_EXP DBL_MIN_EXP
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# if HAVE_FREXP_IN_LIBC && HAVE_LDEXP_IN_LIBC
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# define USE_FREXP_LDEXP
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# define FREXP frexp
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# define LDEXP ldexp
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# endif
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# define DECL_ROUNDING
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# define BEGIN_ROUNDING()
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# define END_ROUNDING()
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# define L_(literal) literal
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#endif
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DOUBLE
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FUNC (DOUBLE x, int *expptr)
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{
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int exponent;
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DECL_ROUNDING
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BEGIN_ROUNDING ();
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#ifdef USE_FREXP_LDEXP
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/* frexp and ldexp are usually faster than the loop below. */
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x = FREXP (x, &exponent);
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x = x + x;
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exponent -= 1;
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if (exponent < MIN_EXP - 1)
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{
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x = LDEXP (x, exponent - (MIN_EXP - 1));
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exponent = MIN_EXP - 1;
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}
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#else
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{
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/* Since the exponent is an 'int', it fits in 64 bits. Therefore the
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loops are executed no more than 64 times. */
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DOUBLE pow2[64]; /* pow2[i] = 2^2^i */
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DOUBLE powh[64]; /* powh[i] = 2^-2^i */
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int i;
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exponent = 0;
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if (x >= L_(1.0))
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{
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/* A nonnegative exponent. */
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{
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DOUBLE pow2_i; /* = pow2[i] */
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DOUBLE powh_i; /* = powh[i] */
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/* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
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x * 2^exponent = argument, x >= 1.0. */
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for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5);
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;
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i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i)
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{
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if (x >= pow2_i)
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{
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exponent += (1 << i);
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x *= powh_i;
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}
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else
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break;
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pow2[i] = pow2_i;
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powh[i] = powh_i;
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}
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}
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/* Here 1.0 <= x < 2^2^i. */
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}
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else
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{
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/* A negative exponent. */
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{
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DOUBLE pow2_i; /* = pow2[i] */
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DOUBLE powh_i; /* = powh[i] */
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/* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
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x * 2^exponent = argument, x < 1.0, exponent >= MIN_EXP - 1. */
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for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5);
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;
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i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i)
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{
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if (exponent - (1 << i) < MIN_EXP - 1)
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break;
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exponent -= (1 << i);
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x *= pow2_i;
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if (x >= L_(1.0))
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break;
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pow2[i] = pow2_i;
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powh[i] = powh_i;
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}
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}
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/* Here either x < 1.0 and exponent - 2^i < MIN_EXP - 1 <= exponent,
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or 1.0 <= x < 2^2^i and exponent >= MIN_EXP - 1. */
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if (x < L_(1.0))
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/* Invariants: x * 2^exponent = argument, x < 1.0 and
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exponent - 2^i < MIN_EXP - 1 <= exponent. */
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while (i > 0)
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{
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i--;
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if (exponent - (1 << i) >= MIN_EXP - 1)
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{
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exponent -= (1 << i);
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x *= pow2[i];
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if (x >= L_(1.0))
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break;
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}
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}
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/* Here either x < 1.0 and exponent = MIN_EXP - 1,
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or 1.0 <= x < 2^2^i and exponent >= MIN_EXP - 1. */
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}
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/* Invariants: x * 2^exponent = argument, and
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either x < 1.0 and exponent = MIN_EXP - 1,
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or 1.0 <= x < 2^2^i and exponent >= MIN_EXP - 1. */
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while (i > 0)
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{
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i--;
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if (x >= pow2[i])
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{
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exponent += (1 << i);
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x *= powh[i];
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}
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}
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/* Here either x < 1.0 and exponent = MIN_EXP - 1,
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or 1.0 <= x < 2.0 and exponent >= MIN_EXP - 1. */
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}
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#endif
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END_ROUNDING ();
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*expptr = exponent;
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return x;
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}
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