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dswap.f 3.5 kB

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  1. *> \brief \b DSWAP
  2. *
  3. * =========== DOCUMENTATION ===========
  4. *
  5. * Online html documentation available at
  6. * http://www.netlib.org/lapack/explore-html/
  7. *
  8. * Definition:
  9. * ===========
  10. *
  11. * SUBROUTINE DSWAP(N,DX,INCX,DY,INCY)
  12. *
  13. * .. Scalar Arguments ..
  14. * INTEGER INCX,INCY,N
  15. * ..
  16. * .. Array Arguments ..
  17. * DOUBLE PRECISION DX(*),DY(*)
  18. * ..
  19. *
  20. *
  21. *> \par Purpose:
  22. * =============
  23. *>
  24. *> \verbatim
  25. *>
  26. *> DSWAP interchanges two vectors.
  27. *> uses unrolled loops for increments equal to 1.
  28. *> \endverbatim
  29. *
  30. * Arguments:
  31. * ==========
  32. *
  33. *> \param[in] N
  34. *> \verbatim
  35. *> N is INTEGER
  36. *> number of elements in input vector(s)
  37. *> \endverbatim
  38. *>
  39. *> \param[in,out] DX
  40. *> \verbatim
  41. *> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
  42. *> \endverbatim
  43. *>
  44. *> \param[in] INCX
  45. *> \verbatim
  46. *> INCX is INTEGER
  47. *> storage spacing between elements of DX
  48. *> \endverbatim
  49. *>
  50. *> \param[in,out] DY
  51. *> \verbatim
  52. *> DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
  53. *> \endverbatim
  54. *>
  55. *> \param[in] INCY
  56. *> \verbatim
  57. *> INCY is INTEGER
  58. *> storage spacing between elements of DY
  59. *> \endverbatim
  60. *
  61. * Authors:
  62. * ========
  63. *
  64. *> \author Univ. of Tennessee
  65. *> \author Univ. of California Berkeley
  66. *> \author Univ. of Colorado Denver
  67. *> \author NAG Ltd.
  68. *
  69. *> \date November 2017
  70. *
  71. *> \ingroup double_blas_level1
  72. *
  73. *> \par Further Details:
  74. * =====================
  75. *>
  76. *> \verbatim
  77. *>
  78. *> jack dongarra, linpack, 3/11/78.
  79. *> modified 12/3/93, array(1) declarations changed to array(*)
  80. *> \endverbatim
  81. *>
  82. * =====================================================================
  83. SUBROUTINE DSWAP(N,DX,INCX,DY,INCY)
  84. *
  85. * -- Reference BLAS level1 routine (version 3.8.0) --
  86. * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
  87. * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  88. * November 2017
  89. *
  90. * .. Scalar Arguments ..
  91. INTEGER INCX,INCY,N
  92. * ..
  93. * .. Array Arguments ..
  94. DOUBLE PRECISION DX(*),DY(*)
  95. * ..
  96. *
  97. * =====================================================================
  98. *
  99. * .. Local Scalars ..
  100. DOUBLE PRECISION DTEMP
  101. INTEGER I,IX,IY,M,MP1
  102. * ..
  103. * .. Intrinsic Functions ..
  104. INTRINSIC MOD
  105. * ..
  106. IF (N.LE.0) RETURN
  107. IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
  108. *
  109. * code for both increments equal to 1
  110. *
  111. *
  112. * clean-up loop
  113. *
  114. M = MOD(N,3)
  115. IF (M.NE.0) THEN
  116. DO I = 1,M
  117. DTEMP = DX(I)
  118. DX(I) = DY(I)
  119. DY(I) = DTEMP
  120. END DO
  121. IF (N.LT.3) RETURN
  122. END IF
  123. MP1 = M + 1
  124. DO I = MP1,N,3
  125. DTEMP = DX(I)
  126. DX(I) = DY(I)
  127. DY(I) = DTEMP
  128. DTEMP = DX(I+1)
  129. DX(I+1) = DY(I+1)
  130. DY(I+1) = DTEMP
  131. DTEMP = DX(I+2)
  132. DX(I+2) = DY(I+2)
  133. DY(I+2) = DTEMP
  134. END DO
  135. ELSE
  136. *
  137. * code for unequal increments or equal increments not equal
  138. * to 1
  139. *
  140. IX = 1
  141. IY = 1
  142. IF (INCX.LT.0) IX = (-N+1)*INCX + 1
  143. IF (INCY.LT.0) IY = (-N+1)*INCY + 1
  144. DO I = 1,N
  145. DTEMP = DX(IX)
  146. DX(IX) = DY(IY)
  147. DY(IY) = DTEMP
  148. IX = IX + INCX
  149. IY = IY + INCY
  150. END DO
  151. END IF
  152. RETURN
  153. END