diff options
Diffstat (limited to 'sysdeps/ieee754/dbl2mpn.c')
| -rw-r--r-- | sysdeps/ieee754/dbl2mpn.c | 107 |
1 files changed, 107 insertions, 0 deletions
diff --git a/sysdeps/ieee754/dbl2mpn.c b/sysdeps/ieee754/dbl2mpn.c new file mode 100644 index 0000000000..6b690f711e --- /dev/null +++ b/sysdeps/ieee754/dbl2mpn.c @@ -0,0 +1,107 @@ +/* Copyright (C) 1993, 1994, 1995 Free Software Foundation, Inc. +This file is part of the GNU C Library. + +The GNU C Library is free software; you can redistribute it and/or +modify it under the terms of the GNU Library General Public License as +published by the Free Software Foundation; either version 2 of the +License, or (at your option) any later version. + +The GNU C Library 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 +Library General Public License for more details. + +You should have received a copy of the GNU Library General Public +License along with the GNU C Library; see the file COPYING.LIB. If +not, write to the Free Software Foundation, Inc., 675 Mass Ave, +Cambridge, MA 02139, USA. */ + +#include "gmp.h" +#include "gmp-impl.h" +#include "longlong.h" +#include "ieee754.h" +#include <float.h> +#include <stdlib.h> + +/* Convert a `double' in IEEE754 standard double-precision format to a + multi-precision integer representing the significand scaled up by its + number of bits (52 for double) and an integral power of two (MPN frexp). */ + +mp_size_t +__mpn_extract_double (mp_ptr res_ptr, mp_size_t size, + int *expt, int *is_neg, + double value) +{ + union ieee754_double u; + u.d = value; + + *is_neg = u.ieee.negative; + *expt = (int) u.ieee.exponent - IEEE754_DOUBLE_BIAS; + +#if BITS_PER_MP_LIMB == 32 + res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction. */ + res_ptr[1] = u.ieee.mantissa0; /* High-order 20 bits. */ + #define N 2 +#elif BITS_PER_MP_LIMB == 64 + /* Hopefully the compiler will combine the two bitfield extracts + and this composition into just the original quadword extract. */ + res_ptr[0] = (u.ieee.mantissa0 << 32) | u.ieee.mantissa1; + #define N 1 +#else + #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for" +#endif +/* The format does not fill the last limb. There are some zeros. */ +#define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \ + - (DBL_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB))) + + if (u.ieee.exponent == 0) + { + /* A biased exponent of zero is a special case. + Either it is a zero or it is a denormal number. */ + if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2. */ + /* It's zero. */ + *expt = 0; + else + { + /* It is a denormal number, meaning it has no implicit leading + one bit, and its exponent is in fact the format minimum. */ + int cnt; + + if (res_ptr[N - 1] != 0) + { + count_leading_zeros (cnt, res_ptr[N - 1]); + cnt -= NUM_LEADING_ZEROS; +#if N == 2 + res_ptr[N - 1] = res_ptr[1] << cnt + | (N - 1) + * (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt)); + res_ptr[0] <<= cnt; +#else + res_ptr[N - 1] <<= cnt; +#endif + *expt = DBL_MIN_EXP - 1 - cnt; + } + else + { + count_leading_zeros (cnt, res_ptr[0]); + if (cnt >= NUM_LEADING_ZEROS) + { + res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS); + res_ptr[0] = 0; + } + else + { + res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt); + res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt); + } + *expt = DBL_MIN_EXP - 1 + - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt; + } + } + } + else + /* Add the implicit leading one bit for a normalized number. */ + res_ptr[N - 1] |= 1 << (DBL_MANT_DIG - 1 - ((N - 1) * BITS_PER_MP_LIMB)); + + return N; +} |