sasum.f (3095B)
1 !> 2 ! @license Apache-2.0 3 ! 4 ! Copyright (c) 2018 The Stdlib Authors. 5 ! 6 ! Licensed under the Apache License, Version 2.0 (the "License"); 7 ! you may not use this file except in compliance with the License. 8 ! You may obtain a copy of the License at 9 ! 10 ! http://www.apache.org/licenses/LICENSE-2.0 11 ! 12 ! Unless required by applicable law or agreed to in writing, software 13 ! distributed under the License is distributed on an "AS IS" BASIS, 14 ! WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 ! See the License for the specific language governing permissions and 16 ! limitations under the License. 17 !< 18 19 !> Computes the sum of absolute values. 20 ! 21 ! ## Notes 22 ! 23 ! * Modified version of reference BLAS level1 routine (version 3.7.0). Updated to "free form" Fortran 95. 24 ! 25 ! ## Authors 26 ! 27 ! * Univ. of Tennessee 28 ! * Univ. of California Berkeley 29 ! * Univ. of Colorado Denver 30 ! * NAG Ltd. 31 ! 32 ! ## History 33 ! 34 ! * Jack Dongarra, linpack, 3/11/78. 35 ! 36 ! - modified 3/93 to return if incx .le. 0. 37 ! - modified 12/3/93, array(1) declarations changed to array(*) 38 ! 39 ! ## License 40 ! 41 ! From <http://netlib.org/blas/faq.html>: 42 ! 43 ! > The reference BLAS is a freely-available software package. It is available from netlib via anonymous ftp and the World Wide Web. Thus, it can be included in commercial software packages (and has been). We only ask that proper credit be given to the authors. 44 ! > 45 ! > Like all software, it is copyrighted. It is not trademarked, but we do ask the following: 46 ! > 47 ! > * If you modify the source for these routines we ask that you change the name of the routine and comment the changes made to the original. 48 ! > 49 ! > * We will gladly answer any questions regarding the software. If a modification is done, however, it is the responsibility of the person who modified the routine to provide support. 50 ! 51 ! @param {integer} N - number of values to sum 52 ! @param {Array<real>} sx - input array 53 ! @param {integer} stride - stride length 54 ! @returns {real} sum of absolute values 55 !< 56 real function sasum( N, sx, stride ) 57 implicit none 58 ! .. 59 ! Scalar arguments: 60 integer :: stride, N 61 ! .. 62 ! Array arguments: 63 real :: sx(*) 64 ! .. 65 ! Local scalars: 66 real :: stemp 67 integer :: nstride, mp1, m, i 68 ! .. 69 ! Intrinsic functions: 70 intrinsic abs, mod 71 ! .. 72 sasum = 0.0e0 73 stemp = 0.0e0 74 ! .. 75 if ( N <= 0 .OR. stride <= 0 ) then 76 return 77 end if 78 ! .. 79 ! If the stride is equal to `1`, use unrolled loops... 80 if ( stride == 1 ) then 81 m = mod( N, 6 ) 82 ! .. 83 ! If we have a remainder, do a clean-up loop... 84 if ( m /= 0 ) then 85 do i = 1, m 86 stemp = stemp + abs( sx( i ) ) 87 end do 88 if ( N < 6 ) then 89 sasum = stemp 90 return 91 end if 92 end if 93 mp1 = m + 1 94 do i = mp1, N, 6 95 stemp = stemp + & 96 abs( sx( i ) ) + abs( sx( i+1 ) ) + & 97 abs( sx( i+2 ) ) + abs( sx( i+3 ) ) + & 98 abs( sx( i+4 ) ) + abs( sx( i+5 ) ) 99 end do 100 else 101 nstride = N * stride 102 do i = 1, nstride, stride 103 stemp = stemp + abs( sx( i ) ) 104 end do 105 end if 106 sasum = stemp 107 return 108 end function sasum