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DOUBLE PRECISION FUNCTION DMACH(JOB)
INTEGER JOB
C
C SMACH COMPUTES MACHINE PARAMETERS OF FLOATING POINT
C ARITHMETIC FOR USE IN TESTING ONLY. NOT REQUIRED BY
C LINPACK PROPER.
C
C IF TROUBLE WITH AUTOMATIC COMPUTATION OF THESE QUANTITIES,
C THEY CAN BE SET BY DIRECT ASSIGNMENT STATEMENTS.
C ASSUME THE COMPUTER HAS
C
C B = BASE OF ARITHMETIC
C T = NUMBER OF BASE B DIGITS
C L = SMALLEST POSSIBLE EXPONENT
C U = LARGEST POSSIBLE EXPONENT
C
C THEN
C
C EPS = B**(1-T)
C TINY = 100.0*B**(-L+T)
C HUGE = 0.01*B**(U-T)
C
C DMACH SAME AS SMACH EXCEPT T, L, U APPLY TO
C DOUBLE PRECISION.
C
C CMACH SAME AS SMACH EXCEPT IF COMPLEX DIVISION
C IS DONE BY
C
C 1/(X+I*Y) = (X-I*Y)/(X**2+Y**2)
C
C THEN
C
C TINY = SQRT(TINY)
C HUGE = SQRT(HUGE)
C
C
C JOB IS 1, 2 OR 3 FOR EPSILON, TINY AND HUGE, RESPECTIVELY.
C
DOUBLE PRECISION EPS,TINY,HUGE,S
C
EPS = 1.0D0
10 EPS = EPS/2.0D0
S = 1.0D0 + EPS
IF (S .GT. 1.0D0) GO TO 10
EPS = 2.0D0*EPS
C
S = 1.0D0
20 TINY = S
S = S/16.0D0
IF (S*1.0 .NE. 0.0D0) GO TO 20
TINY = (TINY/EPS)*100.0
HUGE = 1.0D0/TINY
C
IF (JOB .EQ. 1) DMACH = EPS
IF (JOB .EQ. 2) DMACH = TINY
IF (JOB .EQ. 3) DMACH = HUGE
RETURN
END
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