Annotation of OpenXM_contrib/gmp/mpfr/get_d.c, Revision 1.1
1.1 ! ohara 1: /* mpfr_get_d -- convert a multiple precision floating-point number
! 2: to a machine double precision float
! 3:
! 4: Copyright 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
! 5:
! 6: This file is part of the MPFR Library.
! 7:
! 8: The MPFR Library is free software; you can redistribute it and/or modify
! 9: it under the terms of the GNU Lesser General Public License as published by
! 10: the Free Software Foundation; either version 2.1 of the License, or (at your
! 11: option) any later version.
! 12:
! 13: The MPFR Library is distributed in the hope that it will be useful, but
! 14: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
! 15: or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
! 16: License for more details.
! 17:
! 18: You should have received a copy of the GNU Lesser General Public License
! 19: along with the MPFR Library; see the file COPYING.LIB. If not, write to
! 20: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
! 21: MA 02111-1307, USA. */
! 22:
! 23: #include <float.h>
! 24: #ifndef NO_MATH_DEFS
! 25: #include <math.h>
! 26: #endif
! 27: #include "gmp.h"
! 28: #include "gmp-impl.h"
! 29: #include "longlong.h"
! 30: #include "mpfr.h"
! 31: #include "mpfr-impl.h"
! 32: #include "mpfr-math.h"
! 33:
! 34: static double mpfr_scale2 _PROTO ((double, int));
! 35:
! 36: #define IEEE_DBL_MANT_DIG 53
! 37:
! 38: /* multiplies 1/2 <= d <= 1 by 2^exp */
! 39: static double
! 40: mpfr_scale2 (double d, int exp)
! 41: {
! 42: #if _GMP_IEEE_FLOATS
! 43: {
! 44: union ieee_double_extract x;
! 45:
! 46: if (d == 1.0)
! 47: {
! 48: d = 0.5;
! 49: exp ++;
! 50: }
! 51:
! 52: /* now 1/2 <= d < 1 */
! 53:
! 54: /* infinities and zeroes have already been checked */
! 55: MPFR_ASSERTN(-1073 <= exp && exp <= 1025);
! 56:
! 57: x.d = d;
! 58: if (exp < -1021) /* subnormal case */
! 59: {
! 60: x.s.exp += exp + 52;
! 61: x.d *= DBL_EPSILON;
! 62: }
! 63: else /* normalized case */
! 64: {
! 65: x.s.exp += exp;
! 66: }
! 67: return x.d;
! 68: }
! 69: #else
! 70: {
! 71: double factor;
! 72:
! 73: if (exp < 0)
! 74: {
! 75: factor = 0.5;
! 76: exp = -exp;
! 77: }
! 78: else
! 79: {
! 80: factor = 2.0;
! 81: }
! 82: while (exp != 0)
! 83: {
! 84: if ((exp & 1) != 0)
! 85: d *= factor;
! 86: exp >>= 1;
! 87: factor *= factor;
! 88: }
! 89: return d;
! 90: }
! 91: #endif
! 92: }
! 93:
! 94: /* Assumes IEEE-754 double precision; otherwise, only an approximated
! 95: result will be returned, without any guaranty (and special cases
! 96: such as NaN must be avoided if not supported). */
! 97:
! 98: double
! 99: mpfr_get_d3 (mpfr_srcptr src, mp_exp_t e, mp_rnd_t rnd_mode)
! 100: {
! 101: double d;
! 102: int negative;
! 103:
! 104: if (MPFR_IS_NAN(src))
! 105: return MPFR_DBL_NAN;
! 106:
! 107: negative = MPFR_SIGN(src) < 0;
! 108:
! 109: if (MPFR_IS_INF(src))
! 110: return negative ? MPFR_DBL_INFM : MPFR_DBL_INFP;
! 111:
! 112: if (MPFR_IS_ZERO(src))
! 113: return negative ? -0.0 : 0.0;
! 114:
! 115: /* the smallest normalized number is 2^(-1022)=0.1e-1021, and the smallest
! 116: subnormal is 2^(-1074)=0.1e-1073 */
! 117: if (e < -1073)
! 118: {
! 119: d = negative ?
! 120: (rnd_mode == GMP_RNDD ||
! 121: (rnd_mode == GMP_RNDN && mpfr_cmp_si_2exp(src, -1, -1075) < 0)
! 122: ? -DBL_MIN : -0.0) :
! 123: (rnd_mode == GMP_RNDU ||
! 124: (rnd_mode == GMP_RNDN && mpfr_cmp_si_2exp(src, 1, -1075) > 0)
! 125: ? DBL_MIN : 0.0);
! 126: if (d != 0.0)
! 127: d *= DBL_EPSILON;
! 128: }
! 129: /* the largest normalized number is 2^1024*(1-2^(-53))=0.111...111e1024 */
! 130: else if (e > 1024)
! 131: {
! 132: d = negative ?
! 133: (rnd_mode == GMP_RNDZ || rnd_mode == GMP_RNDU ?
! 134: -DBL_MAX : MPFR_DBL_INFM) :
! 135: (rnd_mode == GMP_RNDZ || rnd_mode == GMP_RNDD ?
! 136: DBL_MAX : MPFR_DBL_INFP);
! 137: }
! 138: else
! 139: {
! 140: int nbits;
! 141: mp_size_t np, i;
! 142: mp_ptr tp;
! 143: int carry;
! 144:
! 145: nbits = IEEE_DBL_MANT_DIG; /* 53 */
! 146: if (e < -1021) /* in the subnormal case, compute the exact number of
! 147: significant bits */
! 148: {
! 149: nbits += (1021 + e);
! 150: MPFR_ASSERTN(nbits >= 1);
! 151: }
! 152: np = (nbits - 1) / BITS_PER_MP_LIMB;
! 153: tp = (mp_ptr) (*__gmp_allocate_func) ((np + 1) * BYTES_PER_MP_LIMB);
! 154: carry = mpfr_round_raw (tp, MPFR_MANT(src), MPFR_PREC(src), negative,
! 155: nbits, rnd_mode, (int *) 0);
! 156: if (carry)
! 157: d = 1.0;
! 158: else
! 159: {
! 160: /* Warning: the rounding may still be incorrect in the rounding
! 161: to the nearest mode when the result is a subnormal because of
! 162: a double rounding (-> 53 bits -> final precision). */
! 163: d = (double) tp[0] / MP_BASE_AS_DOUBLE;
! 164: for (i = 1; i <= np; i++)
! 165: d = (d + tp[i]) / MP_BASE_AS_DOUBLE;
! 166: /* d is the mantissa (between 1/2 and 1) of the argument rounded
! 167: to 53 bits */
! 168: }
! 169: d = mpfr_scale2 (d, e);
! 170: if (negative)
! 171: d = -d;
! 172:
! 173: (*__gmp_free_func) (tp, (np + 1) * BYTES_PER_MP_LIMB);
! 174: }
! 175:
! 176: return d;
! 177: }
! 178:
! 179: /* Note: do not read the exponent if it has no meaning (avoid possible
! 180: traps on some implementations). */
! 181:
! 182: double
! 183: mpfr_get_d (mpfr_srcptr src, mp_rnd_t rnd_mode)
! 184: {
! 185: return mpfr_get_d3 (src, MPFR_IS_FP(src) && MPFR_NOTZERO(src) ?
! 186: MPFR_EXP(src) : 0, rnd_mode);
! 187: }
! 188:
! 189: double
! 190: mpfr_get_d1 (mpfr_srcptr src)
! 191: {
! 192: return mpfr_get_d3 (src, MPFR_IS_FP(src) && MPFR_NOTZERO(src) ?
! 193: MPFR_EXP(src) : 0, __gmp_default_rounding_mode);
! 194: }
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