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Diffstat (limited to 'lib/printf-frexp.c')
| -rw-r--r-- | lib/printf-frexp.c | 188 |
1 files changed, 188 insertions, 0 deletions
diff --git a/lib/printf-frexp.c b/lib/printf-frexp.c new file mode 100644 index 00000000..014c8539 --- /dev/null +++ b/lib/printf-frexp.c @@ -0,0 +1,188 @@ +/* Split a double into fraction and mantissa, for hexadecimal printf. + Copyright (C) 2007 Free Software Foundation, Inc. + + This program is free software: you can redistribute it and/or modify + it under the terms of the GNU Lesser General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with this program. If not, see <http://www.gnu.org/licenses/>. */ + +#include <config.h> + +/* Specification. */ +#ifdef USE_LONG_DOUBLE +# include "printf-frexpl.h" +#else +# include "printf-frexp.h" +#endif + +#include <float.h> +#include <math.h> +#ifdef USE_LONG_DOUBLE +# include "fpucw.h" +#endif + +/* This file assumes FLT_RADIX = 2. If FLT_RADIX is a power of 2 greater + than 2, or not even a power of 2, some rounding errors can occur, so that + then the returned mantissa is only guaranteed to be <= 2.0, not < 2.0. */ + +#ifdef USE_LONG_DOUBLE +# define FUNC printf_frexpl +# define DOUBLE long double +# define MIN_EXP LDBL_MIN_EXP +# if HAVE_FREXPL_IN_LIBC && HAVE_LDEXPL_IN_LIBC +# define USE_FREXP_LDEXP +# define FREXP frexpl +# define LDEXP ldexpl +# endif +# define DECL_ROUNDING DECL_LONG_DOUBLE_ROUNDING +# define BEGIN_ROUNDING() BEGIN_LONG_DOUBLE_ROUNDING () +# define END_ROUNDING() END_LONG_DOUBLE_ROUNDING () +# define L_(literal) literal##L +#else +# define FUNC printf_frexp +# define DOUBLE double +# define MIN_EXP DBL_MIN_EXP +# if HAVE_FREXP_IN_LIBC && HAVE_LDEXP_IN_LIBC +# define USE_FREXP_LDEXP +# define FREXP frexp +# define LDEXP ldexp +# endif +# define DECL_ROUNDING +# define BEGIN_ROUNDING() +# define END_ROUNDING() +# define L_(literal) literal +#endif + +DOUBLE +FUNC (DOUBLE x, int *expptr) +{ + int exponent; + DECL_ROUNDING + + BEGIN_ROUNDING (); + +#ifdef USE_FREXP_LDEXP + /* frexp and ldexp are usually faster than the loop below. */ + x = FREXP (x, &exponent); + + x = x + x; + exponent -= 1; + + if (exponent < MIN_EXP - 1) + { + x = LDEXP (x, exponent - (MIN_EXP - 1)); + exponent = MIN_EXP - 1; + } +#else + { + /* Since the exponent is an 'int', it fits in 64 bits. Therefore the + loops are executed no more than 64 times. */ + DOUBLE pow2[64]; /* pow2[i] = 2^2^i */ + DOUBLE powh[64]; /* powh[i] = 2^-2^i */ + int i; + + exponent = 0; + if (x >= L_(1.0)) + { + /* A nonnegative exponent. */ + { + DOUBLE pow2_i; /* = pow2[i] */ + DOUBLE powh_i; /* = powh[i] */ + + /* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i, + x * 2^exponent = argument, x >= 1.0. */ + for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5); + ; + i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i) + { + if (x >= pow2_i) + { + exponent += (1 << i); + x *= powh_i; + } + else + break; + + pow2[i] = pow2_i; + powh[i] = powh_i; + } + } + /* Here 1.0 <= x < 2^2^i. */ + } + else + { + /* A negative exponent. */ + { + DOUBLE pow2_i; /* = pow2[i] */ + DOUBLE powh_i; /* = powh[i] */ + + /* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i, + x * 2^exponent = argument, x < 1.0, exponent >= MIN_EXP - 1. */ + for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5); + ; + i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i) + { + if (exponent - (1 << i) < MIN_EXP - 1) + break; + + exponent -= (1 << i); + x *= pow2_i; + if (x >= L_(1.0)) + break; + + pow2[i] = pow2_i; + powh[i] = powh_i; + } + } + /* Here either x < 1.0 and exponent - 2^i < MIN_EXP - 1 <= exponent, + or 1.0 <= x < 2^2^i and exponent >= MIN_EXP - 1. */ + + if (x < L_(1.0)) + /* Invariants: x * 2^exponent = argument, x < 1.0 and + exponent - 2^i < MIN_EXP - 1 <= exponent. */ + while (i > 0) + { + i--; + if (exponent - (1 << i) >= MIN_EXP - 1) + { + exponent -= (1 << i); + x *= pow2[i]; + if (x >= L_(1.0)) + break; + } + } + + /* Here either x < 1.0 and exponent = MIN_EXP - 1, + or 1.0 <= x < 2^2^i and exponent >= MIN_EXP - 1. */ + } + + /* Invariants: x * 2^exponent = argument, and + either x < 1.0 and exponent = MIN_EXP - 1, + or 1.0 <= x < 2^2^i and exponent >= MIN_EXP - 1. */ + while (i > 0) + { + i--; + if (x >= pow2[i]) + { + exponent += (1 << i); + x *= powh[i]; + } + } + /* Here either x < 1.0 and exponent = MIN_EXP - 1, + or 1.0 <= x < 2.0 and exponent >= MIN_EXP - 1. */ + } +#endif + + END_ROUNDING (); + + *expptr = exponent; + return x; +} |