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authorjofret2009-04-28 07:17:00 +0000
committerjofret2009-04-28 07:17:00 +0000
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- REAL FUNCTION SLAMCH( CMACH )
-*
-* -- LAPACK auxiliary routine (version 3.0) --
-* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
-* Courant Institute, Argonne National Lab, and Rice University
-* October 31, 1992
-*
-* .. Scalar Arguments ..
- CHARACTER CMACH
-* ..
-*
-* Purpose
-* =======
-*
-* SLAMCH determines single precision machine parameters.
-*
-* Arguments
-* =========
-*
-* CMACH (input) CHARACTER*1
-* Specifies the value to be returned by SLAMCH:
-* = 'E' or 'e', SLAMCH := eps
-* = 'S' or 's , SLAMCH := sfmin
-* = 'B' or 'b', SLAMCH := base
-* = 'P' or 'p', SLAMCH := eps*base
-* = 'N' or 'n', SLAMCH := t
-* = 'R' or 'r', SLAMCH := rnd
-* = 'M' or 'm', SLAMCH := emin
-* = 'U' or 'u', SLAMCH := rmin
-* = 'L' or 'l', SLAMCH := emax
-* = 'O' or 'o', SLAMCH := rmax
-*
-* where
-*
-* eps = relative machine precision
-* sfmin = safe minimum, such that 1/sfmin does not overflow
-* base = base of the machine
-* prec = eps*base
-* t = number of (base) digits in the mantissa
-* rnd = 1.0 when rounding occurs in addition, 0.0 otherwise
-* emin = minimum exponent before (gradual) underflow
-* rmin = underflow threshold - base**(emin-1)
-* emax = largest exponent before overflow
-* rmax = overflow threshold - (base**emax)*(1-eps)
-*
-* =====================================================================
-*
-* .. Parameters ..
- REAL ONE, ZERO
- PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 )
-* ..
-* .. Local Scalars ..
- LOGICAL FIRST, LRND
- INTEGER BETA, IMAX, IMIN, IT
- REAL BASE, EMAX, EMIN, EPS, PREC, RMACH, RMAX, RMIN,
- $ RND, SFMIN, SMALL, T
-* ..
-* .. External Functions ..
- LOGICAL LSAME
- EXTERNAL LSAME
-* ..
-* .. External Subroutines ..
- EXTERNAL SLAMC2
-* ..
-* .. Save statement ..
- SAVE FIRST, EPS, SFMIN, BASE, T, RND, EMIN, RMIN,
- $ EMAX, RMAX, PREC
-* ..
-* .. Data statements ..
- DATA FIRST / .TRUE. /
-* ..
-* .. Executable Statements ..
-*
- IF( FIRST ) THEN
- FIRST = .FALSE.
- CALL SLAMC2( BETA, IT, LRND, EPS, IMIN, RMIN, IMAX, RMAX )
- BASE = BETA
- T = IT
- IF( LRND ) THEN
- RND = ONE
- EPS = ( BASE**( 1-IT ) ) / 2
- ELSE
- RND = ZERO
- EPS = BASE**( 1-IT )
- END IF
- PREC = EPS*BASE
- EMIN = IMIN
- EMAX = IMAX
- SFMIN = RMIN
- SMALL = ONE / RMAX
- IF( SMALL.GE.SFMIN ) THEN
-*
-* Use SMALL plus a bit, to avoid the possibility of rounding
-* causing overflow when computing 1/sfmin.
-*
- SFMIN = SMALL*( ONE+EPS )
- END IF
- END IF
-*
- IF( LSAME( CMACH, 'E' ) ) THEN
- RMACH = EPS
- ELSE IF( LSAME( CMACH, 'S' ) ) THEN
- RMACH = SFMIN
- ELSE IF( LSAME( CMACH, 'B' ) ) THEN
- RMACH = BASE
- ELSE IF( LSAME( CMACH, 'P' ) ) THEN
- RMACH = PREC
- ELSE IF( LSAME( CMACH, 'N' ) ) THEN
- RMACH = T
- ELSE IF( LSAME( CMACH, 'R' ) ) THEN
- RMACH = RND
- ELSE IF( LSAME( CMACH, 'M' ) ) THEN
- RMACH = EMIN
- ELSE IF( LSAME( CMACH, 'U' ) ) THEN
- RMACH = RMIN
- ELSE IF( LSAME( CMACH, 'L' ) ) THEN
- RMACH = EMAX
- ELSE IF( LSAME( CMACH, 'O' ) ) THEN
- RMACH = RMAX
- END IF
-*
- SLAMCH = RMACH
- RETURN
-*
-* End of SLAMCH
-*
- END
-*
-************************************************************************
-*
- SUBROUTINE SLAMC1( BETA, T, RND, IEEE1 )
-*
-* -- LAPACK auxiliary routine (version 3.0) --
-* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
-* Courant Institute, Argonne National Lab, and Rice University
-* October 31, 1992
-*
-* .. Scalar Arguments ..
- LOGICAL IEEE1, RND
- INTEGER BETA, T
-* ..
-*
-* Purpose
-* =======
-*
-* SLAMC1 determines the machine parameters given by BETA, T, RND, and
-* IEEE1.
-*
-* Arguments
-* =========
-*
-* BETA (output) INTEGER
-* The base of the machine.
-*
-* T (output) INTEGER
-* The number of ( BETA ) digits in the mantissa.
-*
-* RND (output) LOGICAL
-* Specifies whether proper rounding ( RND = .TRUE. ) or
-* chopping ( RND = .FALSE. ) occurs in addition. This may not
-* be a reliable guide to the way in which the machine performs
-* its arithmetic.
-*
-* IEEE1 (output) LOGICAL
-* Specifies whether rounding appears to be done in the IEEE
-* 'round to nearest' style.
-*
-* Further Details
-* ===============
-*
-* The routine is based on the routine ENVRON by Malcolm and
-* incorporates suggestions by Gentleman and Marovich. See
-*
-* Malcolm M. A. (1972) Algorithms to reveal properties of
-* floating-point arithmetic. Comms. of the ACM, 15, 949-951.
-*
-* Gentleman W. M. and Marovich S. B. (1974) More on algorithms
-* that reveal properties of floating point arithmetic units.
-* Comms. of the ACM, 17, 276-277.
-*
-* =====================================================================
-*
-* .. Local Scalars ..
- LOGICAL FIRST, LIEEE1, LRND
- INTEGER LBETA, LT
- REAL A, B, C, F, ONE, QTR, SAVEC, T1, T2
-* ..
-* .. External Functions ..
- REAL SLAMC3
- EXTERNAL SLAMC3
-* ..
-* .. Save statement ..
- SAVE FIRST, LIEEE1, LBETA, LRND, LT
-* ..
-* .. Data statements ..
- DATA FIRST / .TRUE. /
-* ..
-* .. Executable Statements ..
-*
- IF( FIRST ) THEN
- FIRST = .FALSE.
- ONE = 1
-*
-* LBETA, LIEEE1, LT and LRND are the local values of BETA,
-* IEEE1, T and RND.
-*
-* Throughout this routine we use the function SLAMC3 to ensure
-* that relevant values are stored and not held in registers, or
-* are not affected by optimizers.
-*
-* Compute a = 2.0**m with the smallest positive integer m such
-* that
-*
-* fl( a + 1.0 ) = a.
-*
- A = 1
- C = 1
-*
-*+ WHILE( C.EQ.ONE )LOOP
- 10 CONTINUE
- IF( C.EQ.ONE ) THEN
- A = 2*A
- C = SLAMC3( A, ONE )
- C = SLAMC3( C, -A )
- GO TO 10
- END IF
-*+ END WHILE
-*
-* Now compute b = 2.0**m with the smallest positive integer m
-* such that
-*
-* fl( a + b ) .gt. a.
-*
- B = 1
- C = SLAMC3( A, B )
-*
-*+ WHILE( C.EQ.A )LOOP
- 20 CONTINUE
- IF( C.EQ.A ) THEN
- B = 2*B
- C = SLAMC3( A, B )
- GO TO 20
- END IF
-*+ END WHILE
-*
-* Now compute the base. a and c are neighbouring floating point
-* numbers in the interval ( beta**t, beta**( t + 1 ) ) and so
-* their difference is beta. Adding 0.25 to c is to ensure that it
-* is truncated to beta and not ( beta - 1 ).
-*
- QTR = ONE / 4
- SAVEC = C
- C = SLAMC3( C, -A )
- LBETA = C + QTR
-*
-* Now determine whether rounding or chopping occurs, by adding a
-* bit less than beta/2 and a bit more than beta/2 to a.
-*
- B = LBETA
- F = SLAMC3( B / 2, -B / 100 )
- C = SLAMC3( F, A )
- IF( C.EQ.A ) THEN
- LRND = .TRUE.
- ELSE
- LRND = .FALSE.
- END IF
- F = SLAMC3( B / 2, B / 100 )
- C = SLAMC3( F, A )
- IF( ( LRND ) .AND. ( C.EQ.A ) )
- $ LRND = .FALSE.
-*
-* Try and decide whether rounding is done in the IEEE 'round to
-* nearest' style. B/2 is half a unit in the last place of the two
-* numbers A and SAVEC. Furthermore, A is even, i.e. has last bit
-* zero, and SAVEC is odd. Thus adding B/2 to A should not change
-* A, but adding B/2 to SAVEC should change SAVEC.
-*
- T1 = SLAMC3( B / 2, A )
- T2 = SLAMC3( B / 2, SAVEC )
- LIEEE1 = ( T1.EQ.A ) .AND. ( T2.GT.SAVEC ) .AND. LRND
-*
-* Now find the mantissa, t. It should be the integer part of
-* log to the base beta of a, however it is safer to determine t
-* by powering. So we find t as the smallest positive integer for
-* which
-*
-* fl( beta**t + 1.0 ) = 1.0.
-*
- LT = 0
- A = 1
- C = 1
-*
-*+ WHILE( C.EQ.ONE )LOOP
- 30 CONTINUE
- IF( C.EQ.ONE ) THEN
- LT = LT + 1
- A = A*LBETA
- C = SLAMC3( A, ONE )
- C = SLAMC3( C, -A )
- GO TO 30
- END IF
-*+ END WHILE
-*
- END IF
-*
- BETA = LBETA
- T = LT
- RND = LRND
- IEEE1 = LIEEE1
- RETURN
-*
-* End of SLAMC1
-*
- END
-*
-************************************************************************
-*
- SUBROUTINE SLAMC2( BETA, T, RND, EPS, EMIN, RMIN, EMAX, RMAX )
-*
-* -- LAPACK auxiliary routine (version 3.0) --
-* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
-* Courant Institute, Argonne National Lab, and Rice University
-* October 31, 1992
-*
-* .. Scalar Arguments ..
- LOGICAL RND
- INTEGER BETA, EMAX, EMIN, T
- REAL EPS, RMAX, RMIN
-* ..
-*
-* Purpose
-* =======
-*
-* SLAMC2 determines the machine parameters specified in its argument
-* list.
-*
-* Arguments
-* =========
-*
-* BETA (output) INTEGER
-* The base of the machine.
-*
-* T (output) INTEGER
-* The number of ( BETA ) digits in the mantissa.
-*
-* RND (output) LOGICAL
-* Specifies whether proper rounding ( RND = .TRUE. ) or
-* chopping ( RND = .FALSE. ) occurs in addition. This may not
-* be a reliable guide to the way in which the machine performs
-* its arithmetic.
-*
-* EPS (output) REAL
-* The smallest positive number such that
-*
-* fl( 1.0 - EPS ) .LT. 1.0,
-*
-* where fl denotes the computed value.
-*
-* EMIN (output) INTEGER
-* The minimum exponent before (gradual) underflow occurs.
-*
-* RMIN (output) REAL
-* The smallest normalized number for the machine, given by
-* BASE**( EMIN - 1 ), where BASE is the floating point value
-* of BETA.
-*
-* EMAX (output) INTEGER
-* The maximum exponent before overflow occurs.
-*
-* RMAX (output) REAL
-* The largest positive number for the machine, given by
-* BASE**EMAX * ( 1 - EPS ), where BASE is the floating point
-* value of BETA.
-*
-* Further Details
-* ===============
-*
-* The computation of EPS is based on a routine PARANOIA by
-* W. Kahan of the University of California at Berkeley.
-*
-* =====================================================================
-*
-* .. Local Scalars ..
- LOGICAL FIRST, IEEE, IWARN, LIEEE1, LRND
- INTEGER GNMIN, GPMIN, I, LBETA, LEMAX, LEMIN, LT,
- $ NGNMIN, NGPMIN
- REAL A, B, C, HALF, LEPS, LRMAX, LRMIN, ONE, RBASE,
- $ SIXTH, SMALL, THIRD, TWO, ZERO
-* ..
-* .. External Functions ..
- REAL SLAMC3
- EXTERNAL SLAMC3
-* ..
-* .. External Subroutines ..
- EXTERNAL SLAMC1, SLAMC4, SLAMC5
-* ..
-* .. Intrinsic Functions ..
- INTRINSIC ABS, MAX, MIN
-* ..
-* .. Save statement ..
- SAVE FIRST, IWARN, LBETA, LEMAX, LEMIN, LEPS, LRMAX,
- $ LRMIN, LT
-* ..
-* .. Data statements ..
- DATA FIRST / .TRUE. / , IWARN / .FALSE. /
-* ..
-* .. Executable Statements ..
-*
- IF( FIRST ) THEN
- FIRST = .FALSE.
- ZERO = 0
- ONE = 1
- TWO = 2
-*
-* LBETA, LT, LRND, LEPS, LEMIN and LRMIN are the local values of
-* BETA, T, RND, EPS, EMIN and RMIN.
-*
-* Throughout this routine we use the function SLAMC3 to ensure
-* that relevant values are stored and not held in registers, or
-* are not affected by optimizers.
-*
-* SLAMC1 returns the parameters LBETA, LT, LRND and LIEEE1.
-*
- CALL SLAMC1( LBETA, LT, LRND, LIEEE1 )
-*
-* Start to find EPS.
-*
- B = LBETA
- A = B**( -LT )
- LEPS = A
-*
-* Try some tricks to see whether or not this is the correct EPS.
-*
- B = TWO / 3
- HALF = ONE / 2
- SIXTH = SLAMC3( B, -HALF )
- THIRD = SLAMC3( SIXTH, SIXTH )
- B = SLAMC3( THIRD, -HALF )
- B = SLAMC3( B, SIXTH )
- B = ABS( B )
- IF( B.LT.LEPS )
- $ B = LEPS
-*
- LEPS = 1
-*
-*+ WHILE( ( LEPS.GT.B ).AND.( B.GT.ZERO ) )LOOP
- 10 CONTINUE
- IF( ( LEPS.GT.B ) .AND. ( B.GT.ZERO ) ) THEN
- LEPS = B
- C = SLAMC3( HALF*LEPS, ( TWO**5 )*( LEPS**2 ) )
- C = SLAMC3( HALF, -C )
- B = SLAMC3( HALF, C )
- C = SLAMC3( HALF, -B )
- B = SLAMC3( HALF, C )
- GO TO 10
- END IF
-*+ END WHILE
-*
- IF( A.LT.LEPS )
- $ LEPS = A
-*
-* Computation of EPS complete.
-*
-* Now find EMIN. Let A = + or - 1, and + or - (1 + BASE**(-3)).
-* Keep dividing A by BETA until (gradual) underflow occurs. This
-* is detected when we cannot recover the previous A.
-*
- RBASE = ONE / LBETA
- SMALL = ONE
- DO 20 I = 1, 3
- SMALL = SLAMC3( SMALL*RBASE, ZERO )
- 20 CONTINUE
- A = SLAMC3( ONE, SMALL )
- CALL SLAMC4( NGPMIN, ONE, LBETA )
- CALL SLAMC4( NGNMIN, -ONE, LBETA )
- CALL SLAMC4( GPMIN, A, LBETA )
- CALL SLAMC4( GNMIN, -A, LBETA )
- IEEE = .FALSE.
-*
- IF( ( NGPMIN.EQ.NGNMIN ) .AND. ( GPMIN.EQ.GNMIN ) ) THEN
- IF( NGPMIN.EQ.GPMIN ) THEN
- LEMIN = NGPMIN
-* ( Non twos-complement machines, no gradual underflow;
-* e.g., VAX )
- ELSE IF( ( GPMIN-NGPMIN ).EQ.3 ) THEN
- LEMIN = NGPMIN - 1 + LT
- IEEE = .TRUE.
-* ( Non twos-complement machines, with gradual underflow;
-* e.g., IEEE standard followers )
- ELSE
- LEMIN = MIN( NGPMIN, GPMIN )
-* ( A guess; no known machine )
- IWARN = .TRUE.
- END IF
-*
- ELSE IF( ( NGPMIN.EQ.GPMIN ) .AND. ( NGNMIN.EQ.GNMIN ) ) THEN
- IF( ABS( NGPMIN-NGNMIN ).EQ.1 ) THEN
- LEMIN = MAX( NGPMIN, NGNMIN )
-* ( Twos-complement machines, no gradual underflow;
-* e.g., CYBER 205 )
- ELSE
- LEMIN = MIN( NGPMIN, NGNMIN )
-* ( A guess; no known machine )
- IWARN = .TRUE.
- END IF
-*
- ELSE IF( ( ABS( NGPMIN-NGNMIN ).EQ.1 ) .AND.
- $ ( GPMIN.EQ.GNMIN ) ) THEN
- IF( ( GPMIN-MIN( NGPMIN, NGNMIN ) ).EQ.3 ) THEN
- LEMIN = MAX( NGPMIN, NGNMIN ) - 1 + LT
-* ( Twos-complement machines with gradual underflow;
-* no known machine )
- ELSE
- LEMIN = MIN( NGPMIN, NGNMIN )
-* ( A guess; no known machine )
- IWARN = .TRUE.
- END IF
-*
- ELSE
- LEMIN = MIN( NGPMIN, NGNMIN, GPMIN, GNMIN )
-* ( A guess; no known machine )
- IWARN = .TRUE.
- END IF
-***
-* Comment out this if block if EMIN is ok
- IF( IWARN ) THEN
- FIRST = .TRUE.
- WRITE( 6, FMT = 9999 )LEMIN
- END IF
-***
-*
-* Assume IEEE arithmetic if we found denormalised numbers above,
-* or if arithmetic seems to round in the IEEE style, determined
-* in routine SLAMC1. A true IEEE machine should have both things
-* true; however, faulty machines may have one or the other.
-*
- IEEE = IEEE .OR. LIEEE1
-*
-* Compute RMIN by successive division by BETA. We could compute
-* RMIN as BASE**( EMIN - 1 ), but some machines underflow during
-* this computation.
-*
- LRMIN = 1
- DO 30 I = 1, 1 - LEMIN
- LRMIN = SLAMC3( LRMIN*RBASE, ZERO )
- 30 CONTINUE
-*
-* Finally, call SLAMC5 to compute EMAX and RMAX.
-*
- CALL SLAMC5( LBETA, LT, LEMIN, IEEE, LEMAX, LRMAX )
- END IF
-*
- BETA = LBETA
- T = LT
- RND = LRND
- EPS = LEPS
- EMIN = LEMIN
- RMIN = LRMIN
- EMAX = LEMAX
- RMAX = LRMAX
-*
- RETURN
-*
- 9999 FORMAT( / / ' WARNING. The value EMIN may be incorrect:-',
- $ ' EMIN = ', I8, /
- $ ' If, after inspection, the value EMIN looks',
- $ ' acceptable please comment out ',
- $ / ' the IF block as marked within the code of routine',
- $ ' SLAMC2,', / ' otherwise supply EMIN explicitly.', / )
-*
-* End of SLAMC2
-*
- END
-*
-************************************************************************
-*
- REAL FUNCTION SLAMC3( A, B )
-*
-* -- LAPACK auxiliary routine (version 3.0) --
-* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
-* Courant Institute, Argonne National Lab, and Rice University
-* October 31, 1992
-*
-* .. Scalar Arguments ..
- REAL A, B
-* ..
-*
-* Purpose
-* =======
-*
-* SLAMC3 is intended to force A and B to be stored prior to doing
-* the addition of A and B , for use in situations where optimizers
-* might hold one of these in a register.
-*
-* Arguments
-* =========
-*
-* A, B (input) REAL
-* The values A and B.
-*
-* =====================================================================
-*
-* .. Executable Statements ..
-*
- SLAMC3 = A + B
-*
- RETURN
-*
-* End of SLAMC3
-*
- END
-*
-************************************************************************
-*
- SUBROUTINE SLAMC4( EMIN, START, BASE )
-*
-* -- LAPACK auxiliary routine (version 3.0) --
-* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
-* Courant Institute, Argonne National Lab, and Rice University
-* October 31, 1992
-*
-* .. Scalar Arguments ..
- INTEGER BASE, EMIN
- REAL START
-* ..
-*
-* Purpose
-* =======
-*
-* SLAMC4 is a service routine for SLAMC2.
-*
-* Arguments
-* =========
-*
-* EMIN (output) EMIN
-* The minimum exponent before (gradual) underflow, computed by
-* setting A = START and dividing by BASE until the previous A
-* can not be recovered.
-*
-* START (input) REAL
-* The starting point for determining EMIN.
-*
-* BASE (input) INTEGER
-* The base of the machine.
-*
-* =====================================================================
-*
-* .. Local Scalars ..
- INTEGER I
- REAL A, B1, B2, C1, C2, D1, D2, ONE, RBASE, ZERO
-* ..
-* .. External Functions ..
- REAL SLAMC3
- EXTERNAL SLAMC3
-* ..
-* .. Executable Statements ..
-*
- A = START
- ONE = 1
- RBASE = ONE / BASE
- ZERO = 0
- EMIN = 1
- B1 = SLAMC3( A*RBASE, ZERO )
- C1 = A
- C2 = A
- D1 = A
- D2 = A
-*+ WHILE( ( C1.EQ.A ).AND.( C2.EQ.A ).AND.
-* $ ( D1.EQ.A ).AND.( D2.EQ.A ) )LOOP
- 10 CONTINUE
- IF( ( C1.EQ.A ) .AND. ( C2.EQ.A ) .AND. ( D1.EQ.A ) .AND.
- $ ( D2.EQ.A ) ) THEN
- EMIN = EMIN - 1
- A = B1
- B1 = SLAMC3( A / BASE, ZERO )
- C1 = SLAMC3( B1*BASE, ZERO )
- D1 = ZERO
- DO 20 I = 1, BASE
- D1 = D1 + B1
- 20 CONTINUE
- B2 = SLAMC3( A*RBASE, ZERO )
- C2 = SLAMC3( B2 / RBASE, ZERO )
- D2 = ZERO
- DO 30 I = 1, BASE
- D2 = D2 + B2
- 30 CONTINUE
- GO TO 10
- END IF
-*+ END WHILE
-*
- RETURN
-*
-* End of SLAMC4
-*
- END
-*
-************************************************************************
-*
- SUBROUTINE SLAMC5( BETA, P, EMIN, IEEE, EMAX, RMAX )
-*
-* -- LAPACK auxiliary routine (version 3.0) --
-* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
-* Courant Institute, Argonne National Lab, and Rice University
-* October 31, 1992
-*
-* .. Scalar Arguments ..
- LOGICAL IEEE
- INTEGER BETA, EMAX, EMIN, P
- REAL RMAX
-* ..
-*
-* Purpose
-* =======
-*
-* SLAMC5 attempts to compute RMAX, the largest machine floating-point
-* number, without overflow. It assumes that EMAX + abs(EMIN) sum
-* approximately to a power of 2. It will fail on machines where this
-* assumption does not hold, for example, the Cyber 205 (EMIN = -28625,
-* EMAX = 28718). It will also fail if the value supplied for EMIN is
-* too large (i.e. too close to zero), probably with overflow.
-*
-* Arguments
-* =========
-*
-* BETA (input) INTEGER
-* The base of floating-point arithmetic.
-*
-* P (input) INTEGER
-* The number of base BETA digits in the mantissa of a
-* floating-point value.
-*
-* EMIN (input) INTEGER
-* The minimum exponent before (gradual) underflow.
-*
-* IEEE (input) LOGICAL
-* A logical flag specifying whether or not the arithmetic
-* system is thought to comply with the IEEE standard.
-*
-* EMAX (output) INTEGER
-* The largest exponent before overflow
-*
-* RMAX (output) REAL
-* The largest machine floating-point number.
-*
-* =====================================================================
-*
-* .. Parameters ..
- REAL ZERO, ONE
- PARAMETER ( ZERO = 0.0E0, ONE = 1.0E0 )
-* ..
-* .. Local Scalars ..
- INTEGER EXBITS, EXPSUM, I, LEXP, NBITS, TRY, UEXP
- REAL OLDY, RECBAS, Y, Z
-* ..
-* .. External Functions ..
- REAL SLAMC3
- EXTERNAL SLAMC3
-* ..
-* .. Intrinsic Functions ..
- INTRINSIC MOD
-* ..
-* .. Executable Statements ..
-*
-* First compute LEXP and UEXP, two powers of 2 that bound
-* abs(EMIN). We then assume that EMAX + abs(EMIN) will sum
-* approximately to the bound that is closest to abs(EMIN).
-* (EMAX is the exponent of the required number RMAX).
-*
- LEXP = 1
- EXBITS = 1
- 10 CONTINUE
- TRY = LEXP*2
- IF( TRY.LE.( -EMIN ) ) THEN
- LEXP = TRY
- EXBITS = EXBITS + 1
- GO TO 10
- END IF
- IF( LEXP.EQ.-EMIN ) THEN
- UEXP = LEXP
- ELSE
- UEXP = TRY
- EXBITS = EXBITS + 1
- END IF
-*
-* Now -LEXP is less than or equal to EMIN, and -UEXP is greater
-* than or equal to EMIN. EXBITS is the number of bits needed to
-* store the exponent.
-*
- IF( ( UEXP+EMIN ).GT.( -LEXP-EMIN ) ) THEN
- EXPSUM = 2*LEXP
- ELSE
- EXPSUM = 2*UEXP
- END IF
-*
-* EXPSUM is the exponent range, approximately equal to
-* EMAX - EMIN + 1 .
-*
- EMAX = EXPSUM + EMIN - 1
- NBITS = 1 + EXBITS + P
-*
-* NBITS is the total number of bits needed to store a
-* floating-point number.
-*
- IF( ( MOD( NBITS, 2 ).EQ.1 ) .AND. ( BETA.EQ.2 ) ) THEN
-*
-* Either there are an odd number of bits used to store a
-* floating-point number, which is unlikely, or some bits are
-* not used in the representation of numbers, which is possible,
-* (e.g. Cray machines) or the mantissa has an implicit bit,
-* (e.g. IEEE machines, Dec Vax machines), which is perhaps the
-* most likely. We have to assume the last alternative.
-* If this is true, then we need to reduce EMAX by one because
-* there must be some way of representing zero in an implicit-bit
-* system. On machines like Cray, we are reducing EMAX by one
-* unnecessarily.
-*
- EMAX = EMAX - 1
- END IF
-*
- IF( IEEE ) THEN
-*
-* Assume we are on an IEEE machine which reserves one exponent
-* for infinity and NaN.
-*
- EMAX = EMAX - 1
- END IF
-*
-* Now create RMAX, the largest machine number, which should
-* be equal to (1.0 - BETA**(-P)) * BETA**EMAX .
-*
-* First compute 1.0 - BETA**(-P), being careful that the
-* result is less than 1.0 .
-*
- RECBAS = ONE / BETA
- Z = BETA - ONE
- Y = ZERO
- DO 20 I = 1, P
- Z = Z*RECBAS
- IF( Y.LT.ONE )
- $ OLDY = Y
- Y = SLAMC3( Y, Z )
- 20 CONTINUE
- IF( Y.GE.ONE )
- $ Y = OLDY
-*
-* Now multiply by BETA**EMAX to get RMAX.
-*
- DO 30 I = 1, EMAX
- Y = SLAMC3( Y*BETA, ZERO )
- 30 CONTINUE
-*
- RMAX = Y
- RETURN
-*
-* End of SLAMC5
-*
- END