| 1 | /* double mpz_get_d_2exp (signed long int *exp, mpz_t src). |
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| 2 | |
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| 3 | Copyright 2001, 2003 Free Software Foundation, Inc. |
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| 4 | |
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| 5 | This file is part of the GNU MP Library. |
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| 6 | |
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| 7 | The GNU MP Library is free software; you can redistribute it and/or modify |
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| 8 | it under the terms of the GNU Lesser General Public License as published by |
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| 9 | the Free Software Foundation; either version 2.1 of the License, or (at your |
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| 10 | option) any later version. |
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| 11 | |
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| 12 | The GNU MP Library is distributed in the hope that it will be useful, but |
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| 13 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
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| 14 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |
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| 15 | License for more details. |
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| 16 | |
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| 17 | You should have received a copy of the GNU Lesser General Public License |
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| 18 | along with the GNU MP Library; see the file COPYING.LIB. If not, write to |
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| 19 | the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
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| 20 | MA 02111-1307, USA. */ |
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| 21 | |
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| 22 | #include "gmp.h" |
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| 23 | #include "gmp-impl.h" |
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| 24 | #include "longlong.h" |
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| 25 | |
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| 26 | double |
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| 27 | mpz_get_d_2exp (signed long int *exp2, mpz_srcptr src) |
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| 28 | { |
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| 29 | double res; |
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| 30 | mp_size_t size, i, n_limbs_to_use; |
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| 31 | int negative; |
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| 32 | mp_ptr qp; |
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| 33 | int cnt; |
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| 34 | |
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| 35 | size = SIZ(src); |
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| 36 | if (size == 0) |
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| 37 | { |
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| 38 | *exp2 = 0; |
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| 39 | return 0.0; |
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| 40 | } |
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| 41 | |
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| 42 | negative = size < 0; |
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| 43 | size = ABS (size); |
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| 44 | qp = PTR(src); |
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| 45 | |
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| 46 | n_limbs_to_use = MIN (LIMBS_PER_DOUBLE, size); |
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| 47 | qp += size - n_limbs_to_use; |
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| 48 | res = qp[0] / MP_BASE_AS_DOUBLE; |
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| 49 | for (i = 1; i < n_limbs_to_use; i++) |
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| 50 | res = (res + qp[i]) / MP_BASE_AS_DOUBLE; |
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| 51 | count_leading_zeros (cnt, qp[n_limbs_to_use - 1]); |
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| 52 | *exp2 = size * BITS_PER_MP_LIMB - cnt; |
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| 53 | res = res * ((mp_limb_t) 1 << cnt); |
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| 54 | |
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| 55 | /* gcc on m68k and x86 holds floats in the coprocessor, which may mean |
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| 56 | "res" has extra precision. Force it through memory to ensure any |
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| 57 | rounding takes place now and won't become 1.0 in the caller. */ |
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| 58 | #if (HAVE_HOST_CPU_FAMILY_m68k || HAVE_HOST_CPU_FAMILY_x86) \ |
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| 59 | && defined (__GNUC__) |
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| 60 | asm ("" : "=m" (res) : "0" (res)); |
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| 61 | #endif |
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| 62 | |
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| 63 | /* if hardware floats are in round upwards mode then res may be 1.0 */ |
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| 64 | if (res >= 1.0) |
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| 65 | { |
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| 66 | res *= 0.5; |
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| 67 | (*exp2)++; |
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| 68 | } |
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| 69 | |
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| 70 | ASSERT (res >= 0.5); |
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| 71 | ASSERT (res < 1.0); |
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| 72 | |
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| 73 | return negative ? -res : res; |
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| 74 | } |
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