github.com/jingcheng-WU/gonum@v0.9.1-0.20210323123734-f1a2a11a8f7b/mathext/internal/amos/amoslib/zdiv.f (about)

     1        SUBROUTINE ZDIV(AR, AI, BR, BI, CR, CI)
     2  C***BEGIN PROLOGUE  ZDIV
     3  C***REFER TO  ZBESH,ZBESI,ZBESJ,ZBESK,ZBESY,ZAIRY,ZBIRY
     4  C
     5  C     DOUBLE PRECISION COMPLEX DIVIDE C=A/B.
     6  C
     7  C***ROUTINES CALLED  ZABS
     8  C***END PROLOGUE  ZDIV
     9        DOUBLE PRECISION AR, AI, BR, BI, CR, CI, BM, CA, CB, CC, CD
    10        DOUBLE PRECISION ZABS
    11        BM = 1.0D0/ZABS(CMPLX(BR,BI,kind=KIND(1.0D0)))
    12        CC = BR*BM
    13        CD = BI*BM
    14        CA = (AR*CC+AI*CD)*BM
    15        CB = (AI*CC-AR*CD)*BM
    16        CR = CA
    17        CI = CB
    18        RETURN
    19        END