sscal.f (3110B)
1 !> 2 ! @license Apache-2.0 3 ! 4 ! Copyright (c) 2019 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 !> Scale a single-precision floating-point vector by a constant. 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 52 ! @param {real} alpha - scalar 53 ! @param {Array<real>} sx - input array 54 ! @param {integer} stride - `sx` stride length 55 !< 56 subroutine sscal( N, alpha, sx, stride ) 57 implicit none 58 ! .. 59 ! Scalar arguments: 60 real :: alpha 61 integer :: stride, N 62 ! .. 63 ! Array arguments: 64 real :: sx(*) 65 ! .. 66 ! Local scalars: 67 integer :: mp1, i, m 68 ! .. 69 ! Intrinsic functions: 70 intrinsic mod 71 ! .. 72 if ( N <= 0 .OR. stride <= 0 ) then 73 return 74 end if 75 ! .. 76 ! If alpha is `1`, then `x` is unchanged... 77 if ( alpha == 1.0 ) then 78 return 79 end if 80 ! .. 81 ! If stride is equal to `1`, use unrolled loops... 82 if ( stride == 1 ) then 83 ! .. 84 ! If we have a remainder, do a clean-up loop... 85 m = mod( N, 5 ) 86 if ( m /= 0 ) then 87 do i = 1, m 88 sx( i ) = alpha * sx( i ) 89 end do 90 if ( N < 5 ) then 91 return 92 end if 93 end if 94 mp1 = m + 1 95 do i = mp1, N, 5 96 sx( i ) = alpha * sx( i ) 97 sx( i+1 ) = alpha * sx( i+1 ) 98 sx( i+2 ) = alpha * sx( i+2 ) 99 sx( i+3 ) = alpha * sx( i+3 ) 100 sx( i+4 ) = alpha * sx( i+4 ) 101 end do 102 return 103 else 104 do i = 1, N*stride, stride 105 sx( i ) = alpha * sx( i ) 106 end do 107 end if 108 return 109 end subroutine sscal