rand_generator.py

"""
    prime modulus multiplicative linear congruential pseudo random number generator
    z[i]=(630360016*z[i-1]) (mod(pow(2,31)-1)), based on Marse Roberts
    multiple 100 streams are supported, with seeds spaced 100000 apart

    usage
    1.  to obtain the next U(0,1) random number from stream, execute
        u=rand(stream), where rand is a double function
        the double variable u will contain the next random number

    2.  to set the seed for stream to desired value zset, execute
        randst(zset, stream)
        where zset must be an integer to the desired seed, 
        a number between 1 and 2147483646 [inclusive]

    3.  to get the current, most recently used, integer in the sequence being generated for stream
        into the int variable zget, execute
        zget=randgt(stream)
        where randgt is a int function
"""

#default seeds for all 100 streams
zrng=[1973272912,  281629770,   20006270, 1280689831, 2096730329, 1933576050, 
     913566091,  246780520, 1363774876,  604901985, 1511192140, 1259851944, 
     824064364,  150493284,  242708531,   75253171, 1964472944, 1202299975, 
     233217322, 1911216000,  726370533,  403498145,  993232223, 1103205531, 
     762430696, 1922803170, 1385516923,   76271663,  413682397,  726466604, 
     336157058, 1432650381, 1120463904,  595778810,  877722890, 1046574445, 
      68911991, 2088367019,  748545416,  622401386, 2122378830,  640690903, 
    1774806513, 2132545692, 2079249579,   78130110,  852776735, 1187867272, 
    1351423507, 1645973084, 1997049139,  922510944, 2045512870,  898585771, 
     243649545, 1004818771,  773686062,  403188473,  372279877, 1901633463, 
     498067494, 2087759558,  493157915,  597104727, 1530940798, 1814496276, 
     536444882, 1663153658,  855503735,   67784357, 1432404475,  619691088, 
     119025595,  880802310,  176192644, 1116780070,  277854671, 1366580350, 
    1142483975, 2026948561, 1053920743,  786262391, 1792203830, 1494667770, 
    1923011392, 1433700034, 1244184613, 1147297105,  539712780, 1545929719, 
     190641742, 1645390429,  264907697,  620389253, 1502074852,  927711160, 
     364849192, 2049576050,  638580085,  547070247]

#the magic constants
modlus  =2147483647
mult1   =24112
mult2   =26143


#generate the next random number
def rand(stream):
    zi=zrng[stream]
    lowprd=(zi&65535)*mult1
    hi=(zi>>16)*mult1+(lowprd>>16)
    zi=((lowprd&65535)-modlus)+((hi&32767)<<16)+(hi>>15)
    if (zi<0):
        zi+=modlus
    lowprd=(zi&65535)*mult2
    hi=(zi>>16)*mult2+(lowprd>>16)
    zi=((lowprd&65535)-modlus)+((hi&32767)<<16)+(hi>>15)
    if (zi<0):
        zi+=modlus
    zrng[stream]=zi
    
    return ((zi>>7|1)+1)/16777216.0


#set the current zrng for stream to zset
def randst(zset, stream):
    zrng[stream]=zset


#return the current zrng for stream
def randgt(stream):
    return zrng[stream]

"""
#validate...
seed=1
print (rand(seed))
"""