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advice for CoderPad users

If you use CoderPad, and the C (or C++) compilers in particular, you might want to be aware of a compile-time option they use that could affect how your programs run.  The gcc compiler is invoked with the -fsanitize=address argument, which can cause heap buffer overflow problems with programs that would otherwise run properly without it, such as the following:


#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

// To execute C, please define "int main()"

int main() {

uint16_t *p, *ibp;

srand(time(NULL));

// causes heap buffer overflows with gcc -fsanitize=address option
// ibp = (uint16_t *)calloc(8, sizeof(uint16_t));
ibp = (uint16_t *)calloc(16, sizeof(uint16_t));
if (ibp == NULL)
   exit(1);

for (p = ibp; p != ibp + 8 * sizeof(uint16_t); p += sizeof(uint16_t)) {
   *p = (rand() % 256) << 8 | (rand() % 256);
}

for (p = ibp; p != ibp + 8 * sizeof(uint16_t); p += sizeof(uint16_t)) {
   printf("%hu\n", *p);
}

free(ibp);
return 0;
}


Execution with the commented assignment to ibp uncommented (ie. halving the allocated memory):


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(no subject)

I'm back, for now.  (I have been posting to FB, LinkedIn, Quora, and Medium.)

Recently, while reading Quora, I happened upon a post suggesting books to use for learning CS (and other related topics) on one's own.  The author, the late Prof. Anany Levitin, has written two books on algorithms (one cowritten with his wife).  From looking at some sample text via Amazon, they cover some of the "problem solving" aspects of algorithms that I have written about in the past.  IMO, these books could serve some people as supplemental material to textbooks such as CLRS, which is more oriented towards (formal) algorithm analysis than design.

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Ciena interview

I had an onsite interview at Ciena a couple of weeks ago for a Senior Systems Test position.  Long story short — I didn't get the job.  I think they were looking for a person with more experience automating the user experience of routers, whereas most of my experience was automating router operations.

Anyway, one good thing came of this.  As I was going through my interview "debriefing" — making notes about what I was asked, how I answered it, and things I could have done better, I found a mistake in the BGP-4 RFC.  I submitted an errata report for it, which will hopefully be helpful to people who use it.

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ProtonMail test

I took a test from 7-9am this morning from ProtonMail, a secure email provider based in Geneva, Switzerland, that has an office in SF.  The test was sent to me by email, and I had two hours to complete it.  ProtonMail required me to take the test during their business hours, so I either had to be up at dawn to take it or stay up really late.  Either way, I knew I would be tired, so I decided the best thing to do would be to take the test first thing in the morning.

The test had several logic puzzles and some other questions.  I have not focused on those types of questions lately, because tech companies are more likely to ask algorithms and systems related questions.  Even if I had prepared more for those types of questions, I still might have struggled with them, because I don't do well on those types of questions after just waking up.  So basically, it's the same old story -- I wish I had done better.


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IBM interview

I had an interview loop yesterday at the IBM Silicon Valley Lab facility with several people from the Cloud Network Services group.  Four engineers plus the engineering manager interviewed me.  I thought my overall performance was so-so -- I could have done worse, but could have done better.  Some of the programming questions I was asked were similar or the same to questions asked some time ago on HackerRank, but I was a little slower at the interview, so I either wasn't able to complete them or made small mistakes.  There were also questions I was asked about past projects that I didn't remember very well.  The air conditioning in the building made me feel very cold, enough to put my jacket on, and impeded my ability to answer questions.  I also started feeling tired after about an hour and a half of the loop.  Perhaps the height of the loop was explaining to one of the team members how Relative Placement works.

Unfortunately, I was turned down.  I am disappointed, but not discouraged.  Hopefully, I will do better on my next interview loop (well enough to get some kind of offer).  Perhaps if I have some time, I will make some general remarks about my experiences with tech interviews over the last couple of years.  (If you read my posts on FB or Quora, you probably have an idea of what I'm going to write.)

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Netsia interview

I had an interview with Netsia last Friday afternoon for a Senior Network Operations Engineer position.  I wasn't offered the position, but I don't feel discouraged.  One of the people interviewing me felt that I would be a good candidate for contract software development work, and that they would consider me if they have any.  I felt pretty good overall about the interview, because I felt like I represented myself.

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(no subject)

I just wanted to briefy mention that I have had a few phone interviews over the past few months that I've felt better about, even though I didn't make it to the next round in any of them.  I have changed my interviewing strategy somewhat.  I am maintaining my focus on IETF working group activities and some other things (such as ranking methods).  So when I do have an interview coming up, I don't just drop everything else to prepare for the interview, although I do attend to specifics the interview might require, such as writing code in a Google Docs document.  When writing code during an interview, I make sure to ask questions, such as if pseudocode is allowed, if I may refer to documentation (e.g. man pages), etc.  If a particular language is required, I check myself as I write for matching braces, etc.  Also, after asking questions, I ask to gather my thoughts for a minute.  If I cannot think of a more efficient algorithm or method, I write the more straightforward code I can think of that would (hopefully) suffice.

In general, I have felt more in control of these interviews than others I've had (and written about here) in the past.  Hopefully, that is a sign of better things to come.
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Facebook job screen

I had a phone screen with a Facebook recruiter earlier today for a position in their network engineering group. They have many interesting projects to support their network infrastructure including datacenter architecture, connectivity, and automation. The screen had two parts – one in which the recruiter asked me some general questions about past jobs and my current activities, and another consisting of directed questions. The questions were generally of the same nature and difficulty as those in this NANOG thread about interview question suitability. I don't remember everything that I was asked, but I made some mistakes. Also, in some cases, I said I could not remember the answer, but would be able to give the answer if I looked it up. The recruiter was nice enough to say that it's expected that I wouldn't be able to answer some questions, because it's been a while since I've worked with these things on a regular basis.

As always, we'll see what happens. I think I could have done better. Everything I was asked is something I have been familiar with (at least) at one time – it's just that I didn't remember some things.
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(no subject)

I was extremely annoyed after spending an hour applying for a Broadcom job. They switched to a new "talent management" provider, so I had to resubmit my resume. Their process of extracting items from a resume is one of the poorest I've used, so I had to correct quite a bit of information. There were several other problems. Perhaps this technology saves time and money for companies looking to hire, but it is very cumbersome and time-consuming for the individuals they seek. Years ago, when people just sent resumes to companies through the postal system, it was an easy process of putting the resume in an envelope, addressing it, stamping it, and dropping it in a mailbox. So much for progress ...
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A mistake, or a sly way of filtering candidates?

Earlier today, I applied for a network development engineer position at Dell. Taleo handles their applications. Part of the application process involves acknowledging having read a Notice of Convictions document. However, at the time I applied for the position, I could not access the document, because I could not obtain an IP address for the domain name in the document's URL.

So here is the dilemma. Would it be better to answer truthfully, indicating that you did not read the document (if you could not access it)? Would it be better to indicate that you did read the document, even though you did not, because you attempted to access it? Or is there some other alternative, but you pay an "opportunity cost" for choosing it (namely the time spent on it)?

I decided to use the "attach" feature Taleo provides to attach a note indicating that I did attempt to access the document, but DNS queries failed (using two different ISPs) for the domain name in the URL. My reasoning was that this is something Taleo (or Dell) may be doing to filter candidates – at the very least, catching those people who were not honest about not reading the document (if they could not access it). It could also serve as a filter for those people who, rather than giving up on a problem, investigate it and attempt to find out what is wrong. Arguably, this is part of the skill set for the position I applied for.

As always, we'll see how it goes. But it did occur to me that this might be a sly way of filtering candidates.