import math

"""
A simple Python class for Slater determinant manipulation
Bit-manipulation stolen from:

http://wiki.python.org/moin/BitManipulation
"""

# bitCount() counts the number of bits set (not an optimal function)

def bitCount(int_type):
    """ Count bits set in integer """
    count = 0
    while(int_type):
        int_type &= int_type - 1
        count += 1
    return(count)


# testBit() returns a nonzero result, 2**offset, if the bit at 'offset' is one.

def testBit(int_type, offset):
    mask = 1 << offset
    return(int_type & mask) >> offset

# setBit() returns an integer with the bit at 'offset' set to 1.

def setBit(int_type, offset):
    mask = 1 << offset
    return(int_type | mask)

# clearBit() returns an integer with the bit at 'offset' cleared.

def clearBit(int_type, offset):
    mask = ~(1 << offset)
    return(int_type & mask)

# toggleBit() returns an integer with the bit at 'offset' inverted, 0 -> 1 and 1 -> 0.

def toggleBit(int_type, offset):
    mask = 1 << offset
    return(int_type ^ mask)

# binary string made from number

def bin0(s):
    return str(s) if s<=1 else bin0(s>>1) + str(s&1)

def bin(s, L = 0):
    ss = bin0(s)
    if L > 0:
        return '0'*(L-len(ss)) + ss
    else:
        return ss
    
    

class Slater:
    """ Class for Slater determinants """
    def __init__(self):
        self.word = int(0)

    def create(self, j):
        print "c^+_" + str(j) + " |" + bin(self.word) + ">  = ",
        # Assume bit j is set, then we return zero.
        s = 0
        # Check if bit j is set.
        isset = testBit(self.word, j)
        if isset == 0:
            bits = bitCount(self.word & ((1<<j)-1))
            s = pow(-1, bits)
            self.word = setBit(self.word, j)

        print str(s) + " x |" + bin(self.word) + ">"
        return s
        
    def annihilate(self, j):
        print "c_" + str(j) + " |" + bin(self.word) + ">  = ",
        # Assume bit j is not set, then we return zero.
        s = 0
        # Check if bit j is set.
        isset = testBit(self.word, j)
        if isset == 1:
            bits = bitCount(self.word & ((1<<j)-1))
            s = pow(-1, bits)
            self.word = clearBit(self.word, j)

        print str(s) + " x |" + bin(self.word) + ">"
        return s



# Do some testing:

phi = Slater()
phi.create(0)
phi.create(1)
phi.create(2)
phi.create(3)

print


s = phi.annihilate(2)
s = phi.create(7)
s = phi.annihilate(0)
s = phi.create(200)