How can I multiply and divide using only bit shifting and adding?

Question

How can I multiply and divide using only bit shifting and adding?

Answer 1

Try this. https://gist.github.com/swguru/5219592

import sys
# implement divide operation without using built-in divide operator
def divAndMod_slow(y,x, debug=0):
    r = 0
    while y >= x:
            r += 1
            y -= x
    return r,y 


# implement divide operation without using built-in divide operator
def divAndMod(y,x, debug=0):

    ## find the highest position of positive bit of the ratio
    pos = -1
    while y >= x:
            pos += 1
            x <<= 1
    x >>= 1
    if debug: print "y=%d, x=%d, pos=%d" % (y,x,pos)

    if pos == -1:
            return 0, y

    r = 0
    while pos >= 0:
            if y >= x:
                    r += (1 << pos)                        
                    y -= x                
            if debug: print "y=%d, x=%d, r=%d, pos=%d" % (y,x,r,pos)

            x >>= 1
            pos -= 1

    return r, y


if __name__ =="__main__":
    if len(sys.argv) == 3:
        y = int(sys.argv[1])
        x = int(sys.argv[2])
     else:
            y = 313271356
            x = 7

print "=== Slow Version ...."
res = divAndMod_slow( y, x)
print "%d = %d * %d + %d" % (y, x, res[0], res[1])

print "=== Fast Version ...."
res = divAndMod( y, x, debug=1)
print "%d = %d * %d + %d" % (y, x, res[0], res[1])