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Diffstat (limited to '2.3-1/src/fortran/lapack/slamch.f')
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diff --git a/2.3-1/src/fortran/lapack/slamch.f b/2.3-1/src/fortran/lapack/slamch.f new file mode 100644 index 00000000..afb4d368 --- /dev/null +++ b/2.3-1/src/fortran/lapack/slamch.f @@ -0,0 +1,857 @@ + 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 |