| 1 | /* __gmp_scale2 -- Scale a double by exponent manipulation. |
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| 2 | |
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| 3 | Copyright 1996, 1997, 1999, 2000, 2001, 2002 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 | |
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| 25 | #ifdef XDEBUG |
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| 26 | #undef _GMP_IEEE_FLOATS |
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| 27 | #endif |
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| 28 | |
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| 29 | #ifndef _GMP_IEEE_FLOATS |
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| 30 | #define _GMP_IEEE_FLOATS 0 |
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| 31 | #endif |
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| 32 | |
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| 33 | double |
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| 34 | __gmp_scale2 (double d, int exp) |
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| 35 | { |
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| 36 | #if _GMP_IEEE_FLOATS |
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| 37 | { |
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| 38 | #if defined (__alpha) && __GNUC__ == 2 && __GNUC_MINOR__ == 8 |
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| 39 | /* Work around alpha-specific bug in GCC 2.8.x. */ |
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| 40 | volatile |
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| 41 | #endif |
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| 42 | union ieee_double_extract x; |
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| 43 | x.d = d; |
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| 44 | exp += x.s.exp; |
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| 45 | x.s.exp = exp; |
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| 46 | if (exp >= 2047) |
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| 47 | { |
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| 48 | /* Return +-infinity */ |
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| 49 | x.s.exp = 2047; |
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| 50 | x.s.manl = x.s.manh = 0; |
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| 51 | } |
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| 52 | else if (exp < 1) |
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| 53 | { |
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| 54 | x.s.exp = 1; /* smallest exponent (biased) */ |
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| 55 | /* Divide result by 2 until we have scaled it to the right IEEE |
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| 56 | denormalized number, but stop if it becomes zero. */ |
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| 57 | while (exp < 1 && x.d != 0) |
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| 58 | { |
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| 59 | x.d *= 0.5; |
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| 60 | exp++; |
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| 61 | } |
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| 62 | } |
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| 63 | return x.d; |
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| 64 | } |
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| 65 | #else |
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| 66 | { |
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| 67 | double factor, r; |
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| 68 | |
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| 69 | factor = 2.0; |
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| 70 | if (exp < 0) |
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| 71 | { |
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| 72 | factor = 0.5; |
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| 73 | exp = -exp; |
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| 74 | } |
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| 75 | r = d; |
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| 76 | if (exp != 0) |
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| 77 | { |
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| 78 | if ((exp & 1) != 0) |
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| 79 | r *= factor; |
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| 80 | exp >>= 1; |
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| 81 | while (exp != 0) |
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| 82 | { |
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| 83 | factor *= factor; |
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| 84 | if ((exp & 1) != 0) |
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| 85 | r *= factor; |
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| 86 | exp >>= 1; |
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| 87 | } |
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| 88 | } |
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| 89 | return r; |
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| 90 | } |
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| 91 | #endif |
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| 92 | } |
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