Diary, February 1996

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  11  12  13  14  15  16  17
  18  19  20  21  22  23  24
  25  26  27  28  29

It is still snowing, although it is not so cold anymore. But what is more remarkable, is that the snow has remained for almost 10 days now.

I have been thinking about announcing this diary on the comp.infosystems.www.announce news group. (follow-up)

This is part of Fractal intuition by David Fowler.

My min_ruler.c program is using up all the otherwise wasted computer cycles of the glasshotel.cs.utwente.nl. Although, it runs on the lowest priority, it used about 92% of the CPU (and only 0.5% of the memory).

I found this in a posting by Peter Seebach in comp.lang.c:

In article <4e4cu4$95f@vixen.cso.uiuc.edu>, HOTARD  <jhotard> wrote:
>I am writing a program that looks at a character and then determines if it is a
>letter or number.  This program must use the switch command ...

main() {
	int c, x, printf();
	c = getchar();
	switch (x = ((c = (unsigned char) c), /* try to ensure a legal char. */
		((!!isdigit(c)) << 1) | ((!!isalpha(c)) << 0)))
	default:
		printf(
	(x == 0 ? "'\\x%x' is neither a letter nor a number.\n" :
	 (x == 1 ? "'%c' is a letter.\n" : (x == 2 ? "'%c' is a number.\n" :
	  (x == 3 ? "'%c' is both a letter and a number.\n" :
	    "'\\x%x' is odd.\n"))), c);
	return 0;
}

About Annabel

(follow-up)

[Added on February 8:]

But do not understand me wrong. I do respect the person who wrote this very much. His knowledge about the English language is far superior to mine. Not so long ago, he said to a student: `You are the first student, who wrote a flawless paragraph'. I got the impression that the student did not grasp the extend of this compliment. Up-to-today, I have not been able to follow the student's example. I also do not have the talent for writing, which this person has, because sometimes he produces a paragraph that would have taken me hours.

Embedded wierd C program

In preparing some materials for a course, I wrote the following program to illustrate that the order of expression evaluation is not determined completely by the precedence of the operators involved. I ran it on every compiler I could find and, not surprisingly, got lots of different answers.

I'd like to get results from this program for as many different compilers as I can to drive home the point that expressions of this sort must be avoided. If you have access to a C compiler other than the ones listed below, I'd be grateful if you could run this program and send me the results. Please include the operating system you are using (if appropriate to the identification of the compiler) and the compiler version number if it has one.

Here's the program (hold on to your hats):

	int main(){
		int i = 10;

		i = i-- - --i * ( i = -3 ) * i++ + ++i;
		printf( "i = %d\n", i );
		return 0;
	}

Results found to date:

21	Borland C/C++ 4.0, Turbo C++ 4.5
-86	Sun 3/50 cc
-85	Sun Sparc cc, SunOS 4.1.4 (a K&R compiler)
4	Sun Sparc acc, SunOS 4.1.4 (an ANSI compiler)
36	DEC VAX/VMS
21	Silicon Graphics Indy, IRIX 5.3
-63	gcc 2.6.3

-63     gcc version 2.4.5

I wonder how many people are going to read my diary now. If you are reading this, please let me know what you think of it. So far, I have never got any email referring to my diary. Someway, I have always thought that only people from the other side of the world would read my diary pages, but now there might be many from inside Holland (I should say the Netherlands) that are going to read my pages.

Again this makes me ask myself the question (that I have asked myself many times before), why do I have this desire of writing my thoughts, ideas and experiences down, and even in a place where it could be read by complete strangers, or what might be worse, people who know me a little.

A pale winter sun

At half past 7, I heard on the morning news that it was freezing 20 degrees Celsius outside. Li-Xia told me that we had three woolen caps, that I could use. I picked the one with Chicago Bulls (follow-up) on it, and used an extra shawl. But still my eyes were tearing when biked to the university.

I had to think about all those people living in Eastern Europe, who would consider -20 a warm winter day.

Online radio show by TROS radio

Because I did not record the broadcast, I emailed their customers service, and asked whether they could provide me a copy on tape. I was very happy, when I received an email from Yvonne van Bellen, to tell me that they send one for free! Thank you!

Serious newsgroups

Hacking a document

Yesterday evening, while doing the dishes, I heard some older man on the Radio refer to his `girl-friend'. Without thought, I assumed that he was not married, but probably living together with her. Then I realized that I always talk about Li-Xia as `my wife'. Suddenly, I realized it would be better to refer to her as my girl-friend, because she is my best female friend.

Wearable camera's

Computer Science: One of the most abstract sciences

Currently, because computer science being a very young science, this is best seen in the confusion that is caused by terminology. If you are a computer scientist, tell me the meaning of the following words: process, task, object, interface, activity and method. (Probably, you can come up with 4 or 5 definitions for each word, especially if you think about other sub-fields of research.)

It would be funny to write a `Concise Computer Science Dictionary'.

About LOTOS

We are using LOTOS in the TransCoop project, as one of our specification languages. LOTOS is an process algebraic language which is based on the concept of synchronization events between processes. Although this is a very powerful concept to model complex behaviour, it does have certain limits in the high-level specification of realistic systems. In such specification, one would like to use a gate (= a channel on which synchronization events take place) to represent the interface between a user and an application, where a single event indicates a operation to be performed, or a message being send. But this fails, because in case there is no synchronization, the reason remains unknown.

The idea that gates in LOTOS can be thought of communication channels between processes, is a misconception that is hard to avoid. From the design of distributed systems it is known that it is impossible to achieve synchronization with an finite number of messages being passed between the distributed components of the system.

How ever, LOTOS can be used to specify the low-level protocols that are used to build distributed systems.

Calculator

Wednesday, February 21, 1996

Snow again

A riddle

So, on Monday morning I sat on the side of the bed and looked in the bag, containing two pairs of unused socks, and immediately saw which pair I had to pick, in order not get confused, and know which was the unused pair the next day. Now, you have to know that I have a bad memory for small details, so marking the socks (by folding them in a special way might not work). I put the new socks on, and put the used pair in the bag with the unused pair. (Notice, that however, that in case I would have had two bags, as most people do, I might have confused the bags, which would both contain one pair of socks.)

On Tuesday morning, I looked in the bag again, and I had indeed forgotten which was the used pair, or how kept them apart. But then I recalled that there was a logical way of determining which was the one that I should put on. And there was only one, and soon I knew which (clean) pair of socks I had to put on.

The riddle is: How could I have done this?

This riddle has been posted in rec.puzzles.

(follow-up)

Funny

The socks riddle

Girvies L. Davis

I came to this page, because yesterday I send an email to The Honourable Lawton Chiles, Governor of Florida, with respect to death penalty of Ricky Roberts.

A traditional Jewish Marriage

There is a striking resemblance between this wedding tradition and the story of Jesus with the church as his bride.

• Jesus drink wine with his disciples at the last supper.
• He paid the highest price, by giving His own life.
• He returned to His Father to prepare rooms for His bride.
• He will come back, as a thief in the night, to get His bride.
• There will be a great wedding feast.

Genesis 3: The Fall of Man

The three kinds of temptations

• The lust of the flesh. `The woman saw that the tree was good for food'. Jesus was tempted to turn stones into bread.
• The lust of the eyes. `The woman saw that it was a delight to the eyes'. Jesus was shown all the kingdoms of the world.
• The boastful pride of life. `The woman saw that the tree was desirable to make one wise'. Jesus was tempted to take pride in that the angles would protect Him from harm.

(follow-up)

The Socks Riddle

You had two identical pairs of socks, and an extra pair. For example, four red socks and two blue. Sunday's socks were red, so you deduced that if you were to wear the blue on Monday, you wouldn't be able to tell the fresh and used red pairs apart on Tuesday. Therefore you left the blue pair for Tuesday.

This would work if you had a good memory, but he stated that he had a bad memory. My assumption was that color, textures, materials (wool vs. silk) and other markings would be non-helpful; Therefore he would have to choose the new pair from current means rather that a past memory. (i.e. smelling them!). :)

Charles' scheme works fine without any memory of colors, textures, etc.

On the first day you wear one pair of red socks, and have a clean red pair and a clean blue pair in the bag.

On the second day you could pick either clean pair to wear next, but you realize that wearing the blue pair will leave you with a problem tomorrow, so you wear the clean red pair, putting the dirty red pair in the bag.

On the third day you don't need to remember which pair in the bag is clean. You simply compare the ones in the bag with the ones on your feet. The ones that resemble the pair you're wearing are dirty, the others (blue) are clean.

You do need to remember your reasoning from day two (which kept you from wearing the blue socks second), but you don't need to remember colors.

A small remark though: On the third day, I did not even remember the reasoning, except that it was logical. And then I deduced from this what it must have been, just like the above people solved the riddle. Actually, that I could deduce it on the second day, gave me the idea to post it as a riddle.

(follow-up)

Tuesday, February 27, 1996

A fragment

---

---

The socks riddle (continued)

Is this the Official answer? I suppose that this answer is the only true "canned" answer (even though a selective memory may rub me the wrong way).

You don't have to remember your reasoning; since it's reasoning, you can reconstruct it from scratch.

Is this the Official answer? I suppose that this answer is the only true "canned" answer (even though a selective memory may rub me the wrong way). Actually he could write his reasoning on a note and tie the note to his finger, but he would have to remember to read the note! .........Thanks for your reasoning!

As I am the poster of the riddle, this can indeed be considered as the official answer, although I could say some more about it. (For example, explain how other combinations of coloured socks would not have worked, and so on ...)

The fact that people were able to solve the riddle, proves that I did not need any information on Tuesday, except that there was a logical argument involved. It was then that I realized I could post it as a riddle.

A talk by Heike Wehrheim

Yesterday's Fragment

Vanilla Tea

At the end of the afternoon, Susan came to show me a drawing [GIF] (redrawn with xfig) which she used to explain something to Jürgen. Or in other words:

Coorporation without notification implies isolation and loss of work.

(next leap day)