sswap.f (3389B)
1 !> 2 ! @license Apache-2.0 3 ! 4 ! Copyright (c) 2020 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 !> Interchanges two single-precision floating-point vectors. 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 12/3/93, array(1) declarations changed to array(*) 37 ! 38 ! ## License 39 ! 40 ! From <http://netlib.org/blas/faq.html>: 41 ! 42 ! > 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. 43 ! > 44 ! > Like all software, it is copyrighted. It is not trademarked, but we do ask the following: 45 ! > 46 ! > * 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. 47 ! > 48 ! > * 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. 49 ! 50 ! @param {integer} N - number of values to swap 51 ! @param {Array<real>} sx - first input array 52 ! @param {integer} strideX - `sx` stride length 53 ! @param {Array<real>} sy - second input array 54 ! @param {integer} strideY - `sy` stride length 55 !< 56 subroutine sswap( N, sx, strideX, sy, strideY ) 57 implicit none 58 ! .. 59 ! Scalar arguments: 60 integer :: strideX, strideY, N 61 ! .. 62 ! Array arguments: 63 real :: sx(*), sy(*) 64 ! .. 65 ! Local scalars: 66 integer :: mp1, ix, iy, i, m 67 real :: tmp 68 ! .. 69 ! Intrinsic functions: 70 intrinsic mod 71 ! .. 72 if ( N <= 0 ) then 73 return 74 end if 75 ! .. 76 ! If both strides are equal to `1`, use unrolled loops... 77 if ( strideX == 1 .AND. strideY == 1 ) then 78 m = mod( N, 3 ) 79 ! .. 80 ! If we have a remainder, do a clean-up loop... 81 if ( m /= 0 ) then 82 do i = 1, m 83 tmp = sx( i ) 84 sx( i ) = sy( i ) 85 sy( i ) = tmp 86 end do 87 if ( N < 3 ) then 88 return 89 end if 90 end if 91 mp1 = m + 1 92 do i = mp1, N, 3 93 tmp = sx( i ) 94 sx( i ) = sy( i ) 95 sy( i ) = tmp 96 97 tmp = sx( i+1 ) 98 sx( i+1 ) = sy( i+1 ) 99 sy( i+1 ) = tmp 100 101 tmp = sx( i+2 ) 102 sx( i+2 ) = sy( i+2 ) 103 sy( i+2 ) = tmp 104 end do 105 else 106 if ( strideX < 0 ) then 107 ix = (-N+1)*strideX + 1 108 else 109 ix = 1 110 end if 111 if ( strideY < 0 ) then 112 iy = (-N+1)*strideY + 1 113 else 114 iy = 1 115 end if 116 do i = 1, N 117 tmp = sx( ix ) 118 sx( ix ) = sy( iy ) 119 sy( iy ) = tmp 120 ix = ix + strideX 121 iy = iy + strideY 122 end do 123 end if 124 return 125 end subroutine sswap