src/numerical/slatec/fortran/zuchk.f

   1 *DECK ZUCHK
   2       SUBROUTINE ZUCHK (YR, YI, NZ, ASCLE, TOL)
   3 C***BEGIN PROLOGUE  ZUCHK
   4 C***SUBSIDIARY
   5 C***PURPOSE  Subsidiary to SERI, ZUOIK, ZUNK1, ZUNK2, ZUNI1, ZUNI2 and
   6 C            ZKSCL
   7 C***LIBRARY   SLATEC
   8 C***TYPE      ALL (CUCHK-A, ZUCHK-A)
   9 C***AUTHOR  Amos, D. E., (SNL)
  10 C***DESCRIPTION
  11 C
  12 C      Y ENTERS AS A SCALED QUANTITY WHOSE MAGNITUDE IS GREATER THAN
  13 C      EXP(-ALIM)=ASCLE=1.0E+3*D1MACH(1)/TOL. THE TEST IS MADE TO SEE
  14 C      IF THE MAGNITUDE OF THE REAL OR IMAGINARY PART WOULD UNDERFLOW
  15 C      WHEN Y IS SCALED (BY TOL) TO ITS PROPER VALUE. Y IS ACCEPTED
  16 C      IF THE UNDERFLOW IS AT LEAST ONE PRECISION BELOW THE MAGNITUDE
  17 C      OF THE LARGEST COMPONENT; OTHERWISE THE PHASE ANGLE DOES NOT HAVE
  18 C      ABSOLUTE ACCURACY AND AN UNDERFLOW IS ASSUMED.
  19 C
  20 C***SEE ALSO  SERI, ZKSCL, ZUNI1, ZUNI2, ZUNK1, ZUNK2, ZUOIK
  21 C***ROUTINES CALLED  (NONE)
  22 C***REVISION HISTORY  (YYMMDD)
  23 C   ??????  DATE WRITTEN
  24 C   910415  Prologue converted to Version 4.0 format.  (BAB)
  25 C***END PROLOGUE  ZUCHK
  26 C
  27 C     COMPLEX Y
  28       DOUBLE PRECISION ASCLE, SS, ST, TOL, WR, WI, YR, YI
  29       INTEGER NZ
  30 C***FIRST EXECUTABLE STATEMENT  ZUCHK
  31       NZ = 0
  32       WR = ABS(YR)
  33       WI = ABS(YI)
  34       ST = MIN(WR,WI)
  35       IF (ST.GT.ASCLE) RETURN
  36       SS = MAX(WR,WI)
  37       ST = ST/TOL
  38       IF (SS.LT.ST) NZ = 1
  39       RETURN
  40       END