1 /* Copyright (C) 1995, 1996, 1997, 2000, 2007 Free Software Foundation, Inc. 2 This file is part of the GNU C Library. 3 4 The GNU C Library is free software; you can redistribute it and/or 5 modify it under the terms of the GNU Lesser General Public 6 License as published by the Free Software Foundation; either 7 version 2.1 of the License, or (at your option) any later version. 8 9 The GNU C Library is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY; without even the implied warranty of 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 12 Lesser General Public License for more details. 13 14 You should have received a copy of the GNU Lesser General Public 15 License along with the GNU C Library; if not, write to the Free 16 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 17 02111-1307 USA. */ 18 19 #include "gmp.h" 20 #include "gmp-impl.h" 21 #include "longlong.h" 22 #include "ieee754.h" 23 #include <float.h> 24 #include <stdlib.h> 25 26 /* Convert a `long double' in IEEE854 standard double-precision format to a 27 multi-precision integer representing the significand scaled up by its 28 number of bits (64 for long double) and an integral power of two 29 (MPN frexpl). */ 30 31 mp_size_t 32 __mpn_extract_long_double (mp_ptr res_ptr, mp_size_t size, 33 int *expt, int *is_neg, 34 long double value) 35 { 36 union ieee854_long_double u; 37 u.d = value; 38 39 *is_neg = u.ieee.negative; 40 *expt = (int) u.ieee.exponent - IEEE854_LONG_DOUBLE_BIAS; 41 42 #if BITS_PER_MP_LIMB == 32 43 res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction. */ 44 res_ptr[1] = u.ieee.mantissa0; /* High-order 32 bits. */ 45 #define N 2 46 #elif BITS_PER_MP_LIMB == 64 47 /* Hopefully the compiler will combine the two bitfield extracts 48 and this composition into just the original quadword extract. */ 49 res_ptr[0] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1; 50 #define N 1 51 #else 52 #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for" 53 #endif 54 55 if (u.ieee.exponent == 0) 56 { 57 /* A biased exponent of zero is a special case. 58 Either it is a zero or it is a denormal number. */ 59 if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2. */ 60 /* It's zero. */ 61 *expt = 0; 62 else 63 { 64 /* It is a denormal number, meaning it has no implicit leading 65 one bit, and its exponent is in fact the format minimum. */ 66 int cnt; 67 68 /* One problem with Intel's 80-bit format is that the explicit 69 leading one in the normalized representation has to be zero 70 for denormalized number. If it is one, the number is according 71 to Intel's specification an invalid number. We make the 72 representation unique by explicitly clearing this bit. */ 73 res_ptr[N - 1] &= ~(1L << ((LDBL_MANT_DIG - 1) % BITS_PER_MP_LIMB)); 74 75 if (res_ptr[N - 1] != 0) 76 { 77 count_leading_zeros (cnt, res_ptr[N - 1]); 78 if (cnt != 0) 79 { 80 #if N == 2 81 res_ptr[N - 1] = res_ptr[N - 1] << cnt 82 | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt)); 83 res_ptr[0] <<= cnt; 84 #else 85 res_ptr[N - 1] <<= cnt; 86 #endif 87 } 88 *expt = LDBL_MIN_EXP - 1 - cnt; 89 } 90 else if (res_ptr[0] != 0) 91 { 92 count_leading_zeros (cnt, res_ptr[0]); 93 res_ptr[N - 1] = res_ptr[0] << cnt; 94 res_ptr[0] = 0; 95 *expt = LDBL_MIN_EXP - 1 - BITS_PER_MP_LIMB - cnt; 96 } 97 else 98 { 99 /* This is the special case of the pseudo denormal number 100 with only the implicit leading bit set. The value is 101 in fact a normal number and so we have to treat this 102 case differently. */ 103 #if N == 2 104 res_ptr[N - 1] = 0x80000000ul; 105 #else 106 res_ptr[0] = 0x8000000000000000ul; 107 #endif 108 *expt = LDBL_MIN_EXP - 1; 109 } 110 } 111 } 112 else if (u.ieee.exponent < 0x7fff 113 #if N == 2 114 && res_ptr[0] == 0 115 #endif 116 && res_ptr[N - 1] == 0) 117 /* Pseudo zero. */ 118 *expt = 0; 119 120 return N; 121 } 122