Print Canonical Addresses of a Site

This 2 lines of Python queries DNS and display the canonical names of a host.  It's like a simple DNS lookup (nslookup).

#!/usr/bin/python

import sys
import socket

HOST=''
PORT=80

if (len(sys.argv) < 2):
 print sys.argv[0], " "
 sys.exit(0)

HOST = sys.argv[1]
for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM):
   print res[4][0]

For example, if we execute the script and pass parameter 'www.google.com', we'd get this:

$ ./getdns.py www.google.com
74.125.224.50
74.125.224.51
74.125.224.48
74.125.224.49
74.125.224.52

Python GUI

This small Python script creates a window application and handles menu events as well as updating statusbar at the bottom.

#!/usr/bin/python

from Tkinter import *
import tkMessageBox

class StatusBar(Frame):

    def __init__(self, master):
        Frame.__init__(self, master)
        self.label = Label(self, text="", bd=1, relief=SUNKEN, anchor=W)
        self.label.pack(side=BOTTOM, fill=X)

    def set(self, format, *args):
        self.label.config(text=format % args)
        self.label.update_idletasks()

    def clear(self):
        self.label.config(text="")
        self.label.update_idletasks()

class App:

    def __init__(self, parent):
        self.this = self
        frame = Frame(parent)
        parent.protocol("WM_DELETE_WINDOW", ConfirmQuit)

        parent.geometry("%dx%d%+d%+d" % (600, 400, 100, 50))

        # create a menu
        menu = Menu(parent)
        parent.config(menu=menu)

        filemenu = Menu(menu)
        menu.add_cascade(label="File", menu=filemenu)
        filemenu.add_command(label="New", command=self.newFile)
        filemenu.add_command(label="Open...", command=self.OpenFile)
        filemenu.add_separator()
        filemenu.add_command(label="Exit", command=self.Exit)

        runmenu = Menu(menu)
        menu.add_cascade(label="Run", menu=runmenu)
        runmenu.add_command(label="Run now", command=self.callback)

        helpmenu = Menu(menu)
        menu.add_cascade(label="Help", menu=helpmenu)
        helpmenu.add_command(label="About...", command=self.About)

    def callback(event):
        print "callback was called from event class ",event.__class__
        print "event.__name__=",__name__
        print "event type:", type(event)
        print "event.this.__class__=", event.this.__class__
        print "this: type=", type(event.this), ",class=", event.this.__class__
        print "status_bar", status_bar.__class__
        status_bar.set("%s", "Ahlan bib")

    def newFile(event):
        print "New file", event
        status_bar.set("%s", "Creating a new file")

    def OpenFile(event):
        print "Open File", event
        status_bar.set("%s", "Opening a file")

    def About(event):
        print "(c) 2012, mlutfi", event
        status_bar.clear()

    def say_hi(self):
        print "hi there, everyone!"

    def Exit(event):
        ConfirmQuit()

class BaseWindow:
    def __init__(self, parent):
        Toplevel()


def ConfirmQuit():
    if tkMessageBox.askokcancel("Quit", "Do you really want to quit?"):
        root.destroy()

root = Tk()
root.protocol("WM_DELETE_WINDOW", ConfirmQuit)

status_bar = StatusBar(root)
status_bar.pack(side=BOTTOM, fill=X)

app = App(root)

root.mainloop()

Fibonacci in Python

# Fibonacci numbers module

def fib(n):    # write Fibonacci series up to n
    a, b = 0, 1
    while b < n:
        #print b,
        a, b = b, a+b

def fib2(n): # return Fibonacci series up to n
    result = []
    a, b = 0, 1
    while b < n:
        result.append(b)
        a, b = b, a+b
    print b
    return result
    
# make it executable as a script as well as module_exit
if __name__ == "__main__":
    import sys
    if (len(sys.argv) > 1):
        f = fib2(int(sys.argv[1]))
        str = ""
        print "Fibonacci sequence: ", f
    else:
        print sys.argv[0], " "

Downloading book "Foundations of Computer Science"

This small python script would download all chapters in the book "Foundations of Computer Science".

#!/usr/bin/python

import sys
from subprocess import call  # for 'call'


urlbase = 'http://infolab.stanford.edu/~ullman/focs/'

others = ['preface.pdf', 'toc.pdf', 'index.pdf']
chapters = range(1,15)
links = []
links.extend(others)

def download(index, f):
    url = urlbase + f
    print "file = ", index+1, url
    call(["wget", url])


for ch in chapters:
    links.append('ch' + '%02d' %(ch) + '.pdf')

out = [download(index,obj) for index,obj in enumerate(links)]

print "out=", out

Regular Expression in Python

The following is a Python snippet to do regular expression. First it reads a file passed as an argument, the it goes to a for-loop for each line and do string regular-expression search

#!/usr/bin/python

import sys # for sys.argv, etc.
import re  # regular expression

if (len(sys.argv) > 1):
    filename = sys.argv[1]
else:
    print sys.argv[0], " "
    sys.exit(0)


with open(filename, 'r') as f:
    #f.read()
    for line in f:
        pattern = re.compile(r"print (.*)")
        match = pattern.search(line)
        if match:
            print "print is used to print '", match.group(1), "'"

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ readfile.py 17,3-9 All "readfile.py" 21L, 386C

Computer Design Fun Party!

1. To compute expression A = (B-C)*(D-E)

Using accumulator:

Load B ; acc = B; opcode=1 B, oper=2B; mem.traf = 2 B

Sub C ; acc = B – C; 1 byte opcode, 2-bytes operand = 3 bytes

Store A ; A = B -C; 1 byte opcode, 2-bytes operand = 3 bytes

Load D ; acc = D; 1 byte opcode, 2-bytes operand = 3 bytes

Sub E ; acc = D -E; 1 byte opcode, 2-bytes operand = 3 bytes

Mul A ; acc = (B-C)* (D-E) ; 1 byte opcode, 2-bytes operand = 3 bytes

Store A ; A = (B-C) * (D-E) ; 1 byte opcode, 2-bytes operand = 3 bytes

Assume each opcode takes 8-bit, operands are 16-bit and data is move in 16-bit chunks:

Total bytes: 7 * 3 byte = 21 bytes

Memory traffic: 21 + 7 * 2 = 35 bytes

Using load-store:

Ld B, r1 ; r1 = B; opcode=1 B, op = 2 B; mem. traff = 2 bytes

Ld C, r2 ; r2 = C; memory traffic = 2 bytes

Sub r1, r2,r3 ; r3 = r1 * r2 = B – C; size=2 bytes, memory traffic = 0

Ld D, r1 ; r1 = D; memory traffic = 2 bytes

Ld E, r2 ; r2 = E; memory traffic = 2 bytes

Sub r1,r2,r4 ; r4 = r1 * r2 = D-E; memory traffic = 0 bytes

Mul r3, r4, r1 ; r1 = r3 * r4 = (B-C) * (D-E); memory traffic = 0 bytes

St r1,A ; A = r1 = (B-C) * (D-E); memory traffic = 2 bytes

Number of bytes for instructions: 3*7 = 21 bytes

Memory traffic: 21 + 5 *2 = 31 bytes

Using stack:

Push B ; mem. Traf = 2 bytes

Push C ; mem. Traf = 2 bytes

Sub ; B – C; mem. Traf. = 2 bytes

Push D ; mem traf = 2 bytes

Push E ; mem.traf = 2 bytes

Sub ; top of the stack contains D-E, below it is B-C

Mul ; top of the stack now contains (B-C) * (D-E)

Each instruction occupies 3 bytes (1 byte opcode and 2-byte operand), so total instructions use 3*7 = 21 bytes.

Memory traffic: 21 + 2*7 = 35 bytes

2. Register 0, 1, 2 (R0, R1, R2) are GPRs. R3 is initialized to 1 and make sure it is unchanged.
   1. Control sequence that forms the 2’s complement difference (or, R0 ← R0 + (-R1) = R0 + 2^’s complement of R1) of the contents of R0 and R1:

Write Enable				A-bus enables				B-bus enables				F0­F1		Time
0	1	2	3	0	1	2	3	0	1	2	3	F0	F1	T
0	1	0	0	0	1	0	0	0	0	0	0	1	1	0
0	1	0	0	0	1	0	0	0	0	0	1	0	0	1
1	0	0	0	1	1	0	0	1	0	0	0	0	0	2

Explanation:

At T=0:

F₀F₁ = 11 (A’), A-bus enable = 1, B-bus enable = all zeros. Data (say, Y) is placed in A-bus. C-bus contains Y’, Write-enable = pin 1. So Y is written to register 1 (R1 = Y’).

At T = 1:

F₀F₁ = 00 (add), A-bus enable = pin 1 (content of R1 which is X, is in A-bus), B-bus enable= pin 3 (content of R3 which is 1 is in B-bus), write-enable = pin 1 (C-bus contains Y’ + 1). So R1 = Y’ + 1 = 2’s compl. Of X.(or R1 = -Y)

At T = 2

B-bus = 0, hence data from R0, say X, is placed in B-bus. F₀F₁ = 00 (add), A-bus enable = 1 (which contains –Y). C-bus contains R0 + R1 = X - Y . Write-enable = pin 0, so result is stored in R0.

2. R0 XOR R1 (R0’ & R1 + R0 & R1’) = (R0 + R1)(R0’ + R1’), leaving the result in R0.

Write Enable				A-bus enables				B-bus enables				F0­F1		Time	Note
0	1	2	3	0	1	2	3	0	1	2	3	F0	F1	T	(Movements etc.)
0	0	1	0	1	0	0	0	0	1	0	0	0	0	0	R2 ← A + B
1	0	0	0	1	0	0	0	0	0	0	0	1	1	1	R0 ← A’
0	1	0	0	0	1	0	0	0	0	0	0	1	1	2	R1 ← B’
0	1	0	0	1	0	0	0	0	1	0	0	0	0	3	R1 ← A’ + B’
1	0	0	0	0	1	0	0	0	0	1		0	1	4	R0 ← (A+B)&(A’+B’)

3. Booth Multiplication Algorithm:

/***********************************************************
Title: Booth Algorithm sample
Desc: To simulate booth multiplication algorithm
Author: Buhadram
Notes:

Ref:
- Computer Architecture: A Quantitative Approach
*************************************************************/
#include 
#include 
#include 
#include 

#define NUMTYPE	   	short int
#define NUMBITS		(8*sizeof(NUMTYPE))
#define MAX(x,y) 		((x) > (y) ? x : y)
#define MIN(x,y) 		((x) < (y) ? x : y)
#define BITMASK(x,mask) 	((x) & mask)
/*********************************
proc: bitmask
desc: return 1 if bit[pos] is set
      pos=0 for LSB, and p=sizeof(x)-1
      for MSB
*********************************/
#define BIT(x,pos)		( (BITMASK(x,1<<(pos))) >> (pos) )
#define ASCII_BIT(x)	((x) + '0')

char *get_input(const char *prompt, char *buf, int length)
{
	char *p;
	int i;
    printf("%s",prompt);
	// fgets is safer to avoid buffer overflow
	p = fgets(buf, length, stdin);
	// remove newline character
	buf[strlen(buf)-1] = 0;
	return p;
}

/********************************************
* Swapbits
* Desc: To swap bit orders, e.g LSB becomes MSB
        Note: b[0] is LSB, b[n-1] is MSB
********************************************/
void swapbits(NUMTYPE *b)
{
    int i;
    int tmp;

	tmp = 0;
	for(i=0; i base)
       base = 10;                    /* can only use 0-9, A-Z        */
    tail = &buf[BUFSIZE - 1];           /* last character position      */
    *tail-- = '\0';

    if (10 == base && N < 0L) {
	   *head++ = '-';
       uarg = -N;
    }
    else uarg = N;

    if (uarg) {
  	   	for (i = 1; uarg; ++i) {
       	   register ldiv_t r;
		   r = ldiv(uarg, base);
           *tail-- = (char)(r.rem + ((9L < r.rem) ? ('A' - 10L) : '0'));
           uarg    = r.quot;
    	}
    }
    else  *tail-- = '0';
	memcpy(head, ++tail, i);
    return str;
}

#endif


/******************************
proc: btol
desc: converts binary string to
	  long integer
******************************/
long btol(const char *bin)
{
    int n,i;
    long d;

	n = strlen(bin);
	d = 0;
	for(i=n-1; i>=0; i--) {
		d += (bin[i]-'0') * (1 << i);
    }
    return d;
}

/**************************************
Proc: Ashift_bits_right
desc: perform arithmetic shift right on
    bits in x, but preserving the sign bit.
***************************************/
void ashift_bits_right(long *x, int numbits)
{
    int neg;

    neg = (*x<0) ? 1 : 0;
    *x >>= numbits;

    if (neg)
       //*x |= (1<>= 1;
		qm = q0;
		q >>= 1;
		if (a0)
		   r |= b1;
		b1 <<= 1;
    }
    return r;
}


int main(int argc, char *argv[])
{
	#define BUF_SIZE	(1024+1)
	char *buf;
	NUMTYPE A, B;
	long res;
	char str[256];

	buf = (char *)malloc(BUF_SIZE+1);
	assert(buf);
    get_input("A = ", buf, BUF_SIZE);
    A = atol(buf);
    printf("A (in Binary) = %s\n", ltoa(A, str, 2));
    get_input("B = ", buf, BUF_SIZE);
    B = atol(buf);
    printf("B (in Binary) = %s\n", ltoa(B, str, 2));
    res = A+B;
    printf("A + B = %ld = 0x%0X\n", res, res);
    res = A - B;
	printf("A - B = %ld = 0x%0X\n", res, res);
    puts("\n\nBOOTH MULTIPLICATION\n");
    res = booth_mult(A,B);
	printf("A * B = %ld = 0x%0X = %sb\n", res, res, ltoa(B,str,2));
    free(buf);
	return 0;
}