| Austin Schuh | dace2a6 | 2020-08-18 10:56:48 -0700 | [diff] [blame] | 1 | /* mpf_get_si -- mpf to long conversion |
| 2 | |
| 3 | Copyright 2001, 2002, 2004 Free Software Foundation, Inc. |
| 4 | |
| 5 | This file is part of the GNU MP Library. |
| 6 | |
| 7 | The GNU MP Library is free software; you can redistribute it and/or modify |
| 8 | it under the terms of either: |
| 9 | |
| 10 | * the GNU Lesser General Public License as published by the Free |
| 11 | Software Foundation; either version 3 of the License, or (at your |
| 12 | option) any later version. |
| 13 | |
| 14 | or |
| 15 | |
| 16 | * the GNU General Public License as published by the Free Software |
| 17 | Foundation; either version 2 of the License, or (at your option) any |
| 18 | later version. |
| 19 | |
| 20 | or both in parallel, as here. |
| 21 | |
| 22 | The GNU MP Library is distributed in the hope that it will be useful, but |
| 23 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
| 24 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 25 | for more details. |
| 26 | |
| 27 | You should have received copies of the GNU General Public License and the |
| 28 | GNU Lesser General Public License along with the GNU MP Library. If not, |
| 29 | see https://www.gnu.org/licenses/. */ |
| 30 | |
| 31 | #include "gmp-impl.h" |
| 32 | |
| 33 | |
| 34 | /* Any fraction bits are truncated, meaning simply discarded. |
| 35 | |
| 36 | For values bigger than a long, the low bits are returned, like |
| 37 | mpz_get_si, but this isn't documented. |
| 38 | |
| 39 | Notice this is equivalent to mpz_set_f + mpz_get_si. |
| 40 | |
| 41 | |
| 42 | Implementation: |
| 43 | |
| 44 | fl is established in basically the same way as for mpf_get_ui, see that |
| 45 | code for explanations of the conditions. |
| 46 | |
| 47 | However unlike mpf_get_ui we need an explicit return 0 for exp<=0. When |
| 48 | f is a negative fraction (ie. size<0 and exp<=0) we can't let fl==0 go |
| 49 | through to the zany final "~ ((fl - 1) & LONG_MAX)", that would give |
| 50 | -0x80000000 instead of the desired 0. */ |
| 51 | |
| 52 | long |
| 53 | mpf_get_si (mpf_srcptr f) __GMP_NOTHROW |
| 54 | { |
| 55 | mp_exp_t exp; |
| 56 | mp_size_t size, abs_size; |
| 57 | mp_srcptr fp; |
| 58 | mp_limb_t fl; |
| 59 | |
| 60 | exp = EXP (f); |
| 61 | size = SIZ (f); |
| 62 | fp = PTR (f); |
| 63 | |
| 64 | /* fraction alone truncates to zero |
| 65 | this also covers zero, since we have exp==0 for zero */ |
| 66 | if (exp <= 0) |
| 67 | return 0L; |
| 68 | |
| 69 | /* there are some limbs above the radix point */ |
| 70 | |
| 71 | fl = 0; |
| 72 | abs_size = ABS (size); |
| 73 | if (abs_size >= exp) |
| 74 | fl = fp[abs_size-exp]; |
| 75 | |
| 76 | #if BITS_PER_ULONG > GMP_NUMB_BITS |
| 77 | if (exp > 1 && abs_size+1 >= exp) |
| 78 | fl |= fp[abs_size - exp + 1] << GMP_NUMB_BITS; |
| 79 | #endif |
| 80 | |
| 81 | if (size > 0) |
| 82 | return fl & LONG_MAX; |
| 83 | else |
| 84 | /* this form necessary to correctly handle -0x80..00 */ |
| 85 | return -1 - (long) ((fl - 1) & LONG_MAX); |
| 86 | } |