myhdl/example/arith_lib/PrefixAnd.py

from myhdl import Signal, intbv

from arith_utils import log2ceil
from arith_utils import SLOW, MEDIUM, FAST

def PrefixAnd(width, speed, PI, PO):

    n = width
    m = log2ceil(width)

    def fastPrefix():
        PT = Signal(intbv(0))
        while 1:
            yield PI, PT
            PT.next[n:] = PI
            for l in range(1, m+1):
                for k in range(2**(m-l)):
                    for i in range(2**(l-1)):
                        if (k*2**l + i) < n:
                            PT.next[l*n + k*2**l + i] = \
                                PT[(l-1)*n + k*2**l + i]
                        if (k*2**l + 2**(l-1) + i) < n:
                            PT.next[l*n + k*2**l + 2**(l-1) + i] = \
                                PT[(l-1)*n + k*2**l + 2**(l-1) + i] & \
                                PT[(l-1)*n + k*2**l + 2**(l-1) - 1]
            PO.next = PT[(m+1)*n:m*n]

    def slowPrefix():
        PT = Signal(intbv(0))
        while 1:
            yield PI, PT
            PT.next[0] = PI[0]
            for i in range(1, n):
                PT.next[i] = PI[i] & PT[i-1]
            PO.next = PT

    if speed == SLOW:
        return slowPrefix()
    elif speed == FAST:
        return fastPrefix()
    else:
        raise NotImplementedError