Line data Source code
1 : !--------------------------------------------------------------------------------------------------! 2 : ! CP2K: A general program to perform molecular dynamics simulations ! 3 : ! Copyright 2000-2024 CP2K developers group <https://cp2k.org> ! 4 : ! ! 5 : ! SPDX-License-Identifier: GPL-2.0-or-later ! 6 : !--------------------------------------------------------------------------------------------------! 7 : 8 : ! ************************************************************************************************** 9 : !> \brief Functions which are common to different hash tables 10 : !> Derived from qs_fb_hash_table_types and qs_fb_hash_table_types (Mark Tucker, Jun 2016) 11 : ! ************************************************************************************************** 12 : MODULE qs_hash_table_functions 13 : 14 : #include "./base/base_uses.f90" 15 : IMPLICIT NONE 16 : 17 : PRIVATE 18 : 19 : ! public methods 20 : PUBLIC :: hash_table_matching_prime 21 : 22 : CHARACTER(len=*), PARAMETER, PRIVATE :: moduleN = 'qs_hash_table_functions' 23 : 24 : CONTAINS 25 : 26 : ! ************************************************************************************************** 27 : !> \brief Find a prime number equal or larger than ii 28 : !> \param ii : input integer 29 : !> \return : the prime number 30 : ! ************************************************************************************************** 31 22977 : PURE FUNCTION hash_table_matching_prime(ii) RESULT(res) 32 : INTEGER, INTENT(IN) :: ii 33 : INTEGER :: res 34 : 35 : ! even numbers are not prime, so no point testing them, so increment by 2 each time starting 36 : ! from an odd number greater or equal to ii (as noted in \brief) 37 22977 : res = ii + 1 - MOD(ii, 2) 38 : 39 34498 : DO WHILE (.NOT. is_positive_prime(res)) 40 11521 : res = res + 2 41 : END DO 42 22977 : END FUNCTION hash_table_matching_prime 43 : 44 : ! ************************************************************************************************** 45 : !> \brief Check if a number is a positive prime 46 : !> \param num : number to check 47 : !> \return : returns TRUE if num is a positive prime, FALSE otherwise 48 : !> \author Lianheng Tong (LT) lianheng.tong@kcl.ac.uk 49 : ! ************************************************************************************************** 50 34498 : PURE FUNCTION is_positive_prime(num) RESULT(res) 51 : INTEGER, INTENT(IN) :: num 52 : LOGICAL :: res 53 : 54 : INTEGER :: ii 55 : 56 34498 : IF (num .LE. 3) THEN 57 : res = .FALSE. 58 : RETURN 59 : END IF 60 30043 : IF (MOD(num, 2) == 0 .OR. MOD(num, 3) == 0) THEN 61 : res = .FALSE. 62 : RETURN 63 : END IF 64 : 65 : ! all primes > 3 are of the form 6*kk +/- 1, kk=1,2,3... 66 : ! (although not all 6*kk +/- 1 is a prime); 67 : ! and we only have to check factors less than and equal to SQRT(num) 68 : ii = 5 69 25345 : DO WHILE (ii*ii .LE. num) 70 2368 : IF (MOD(num, ii) == 0 .OR. MOD(num, ii + 2) == 0) THEN 71 : res = .FALSE. 72 : RETURN 73 : END IF 74 1558 : ii = ii + 6 75 : END DO 76 : res = .TRUE. 77 : END FUNCTION is_positive_prime 78 : 79 : END MODULE qs_hash_table_functions 80 :