+++ /dev/null
- double precision function randlc(x, a)
-
-c---------------------------------------------------------------------
-c
-c This routine returns a uniform pseudorandom double precision number in the
-c range (0, 1) by using the linear congruential generator
-c
-c x_{k+1} = a x_k (mod 2^46)
-c
-c where 0 < x_k < 2^46 and 0 < a < 2^46. This scheme generates 2^44 numbers
-c before repeating. The argument A is the same as 'a' in the above formula,
-c and X is the same as x_0. A and X must be odd double precision integers
-c in the range (1, 2^46). The returned value RANDLC is normalized to be
-c between 0 and 1, i.e. RANDLC = 2^(-46) * x_1. X is updated to contain
-c the new seed x_1, so that subsequent calls to RANDLC using the same
-c arguments will generate a continuous sequence.
-
- implicit none
- double precision x, a
- integer*8 i246m1, Lx, La
- double precision d2m46
-
- parameter(d2m46=0.5d0**46)
-
- save i246m1
- data i246m1/X'00003FFFFFFFFFFF'/
-
- Lx = X
- La = A
-
- Lx = iand(Lx*La,i246m1)
- randlc = d2m46*dble(Lx)
- x = dble(Lx)
- return
- end
-
-
-c---------------------------------------------------------------------
-c---------------------------------------------------------------------
-
-
- SUBROUTINE VRANLC (N, X, A, Y)
- implicit none
- integer n, i
- double precision x, a, y(*)
- integer*8 i246m1, Lx, La
- double precision d2m46
-
-c This doesn't work, because the compiler does the calculation in 32
-c bits and overflows. No standard way (without f90 stuff) to specify
-c that the rhs should be done in 64 bit arithmetic.
-c parameter(i246m1=2**46-1)
-
- parameter(d2m46=0.5d0**46)
-
- save i246m1
- data i246m1/X'00003FFFFFFFFFFF'/
-
-c Note that the v6 compiler on an R8000 does something stupid with
-c the above. Using the following instead (or various other things)
-c makes the calculation run almost 10 times as fast.
-c
-c save d2m46
-c data d2m46/0.0d0/
-c if (d2m46 .eq. 0.0d0) then
-c d2m46 = 0.5d0**46
-c endif
-
- Lx = X
- La = A
- do i = 1, N
- Lx = iand(Lx*La,i246m1)
- y(i) = d2m46*dble(Lx)
- end do
- x = dble(Lx)
-
- return
- end
-
