1 /* mpz_fac_ui(RESULT, N) -- Set RESULT to N!. 2 3 Contributed to the GNU project by Marco Bodrato. 4 5 Copyright 1991, 1993, 1994, 1995, 2000, 2001, 2002, 2003, 2011, 2012 6 Free Software Foundation, Inc. 7 8 This file is part of the GNU MP Library. 9 10 The GNU MP Library is free software; you can redistribute it and/or modify 11 it under the terms of the GNU Lesser General Public License as published by 12 the Free Software Foundation; either version 3 of the License, or (at your 13 option) any later version. 14 15 The GNU MP Library is distributed in the hope that it will be useful, but 16 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 17 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 18 License for more details. 19 20 You should have received a copy of the GNU Lesser General Public License 21 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 22 23 #include "gmp.h" 24 #include "gmp-impl.h" 25 26 #define FACTOR_LIST_STORE(P, PR, MAX_PR, VEC, I) \ 27 do { \ 28 if ((PR) > (MAX_PR)) { \ 29 (VEC)[(I)++] = (PR); \ 30 (PR) = (P); \ 31 } else \ 32 (PR) *= (P); \ 33 } while (0) 34 35 #if TUNE_PROGRAM_BUILD 36 #define FACTORS_PER_LIMB (GMP_NUMB_BITS / (LOG2C(FAC_DSC_THRESHOLD_LIMIT-1)+1)) 37 #else 38 #define FACTORS_PER_LIMB (GMP_NUMB_BITS / (LOG2C(FAC_ODD_THRESHOLD)+1)) 39 #endif 40 41 /* Computes n!, the factorial of n. 42 WARNING: it assumes that n fits in a limb! 43 */ 44 void 45 mpz_fac_ui (mpz_ptr x, unsigned long n) 46 { 47 static const mp_limb_t table[] = { ONE_LIMB_FACTORIAL_TABLE }; 48 49 ASSERT (n <= GMP_NUMB_MAX); 50 51 if (n < numberof (table)) 52 { 53 PTR (x)[0] = table[n]; 54 SIZ (x) = 1; 55 } 56 else if (BELOW_THRESHOLD (n, FAC_ODD_THRESHOLD)) 57 { 58 mp_limb_t prod, max_prod; 59 mp_size_t j; 60 mp_ptr factors; 61 TMP_SDECL; 62 63 TMP_SMARK; 64 factors = TMP_SALLOC_LIMBS (2 + (n - numberof (table)) / FACTORS_PER_LIMB); 65 66 factors[0] = table[numberof (table)-1]; 67 j = 1; 68 prod = n; 69 #if TUNE_PROGRAM_BUILD 70 max_prod = GMP_NUMB_MAX / FAC_DSC_THRESHOLD_LIMIT; 71 #else 72 max_prod = GMP_NUMB_MAX / (FAC_ODD_THRESHOLD | 1); 73 #endif 74 while (--n >= numberof (table)) 75 FACTOR_LIST_STORE (n, prod, max_prod, factors, j); 76 77 factors[j++] = prod; 78 mpz_prodlimbs (x, factors, j); 79 80 TMP_SFREE; 81 } 82 else 83 { 84 mp_limb_t count; 85 mpz_oddfac_1 (x, n, 0); 86 if (n <= TABLE_LIMIT_2N_MINUS_POPC_2N) 87 count = __gmp_fac2cnt_table[n / 2 - 1]; 88 else 89 { 90 popc_limb (count, n); 91 count = n - count; 92 } 93 mpz_mul_2exp (x, x, count); 94 } 95 } 96 97 #undef FACTORS_PER_LIMB 98 #undef FACTOR_LIST_STORE 99