Older blog entries for rmathew (starting at number 144)

13 Feb 2006 (updated 13 Feb 2006 at 07:00 UTC) »
C99
In a personal project, I have been using some of the niftier and simpler C99 features like //-style comments, mixed variable declarations and statements, the bool type with its true and false pre-defined values and the uint16_t, int32_t, etc. integral types from stdint.h. They resolve some of the minor irritants I used to face when I am forced to code in C89. I plan to use these features from C99 in all my personal projects written in C.

Unfortunately, compiler vendors do not seem too eager to support all the features in C99 even after a better part of a decade after the standard was released! Microsoft is surely not in a hurry to support C99 and GCC and glibc are still not completely there yet. A sad state of affairs. Either the standards committee was eager to get new features into C without a buy-in from the compiler vendors or the C coders have been a little underwhelmed with these features and hence have not been pushing for support for them in their compilers.

IITs All About
Someone has uploaded CBS's "60 Minutes" feature on the IITs to Google Video (thanks to Arpana for pointing me to this). There is a lot of truth accompanied by the usual hyperbole in this video with unfortunately some of the interviewed students also playing along. For instance, not everyone likes to stay up all night preparing for examinations, that too accompanied by a doting tea-making mother. Certainly not everyone has their entire family dropping them off at the examination centre and has them hanging around for the entire duration of the examination. "Puh-sycho!" It is also too much of a stretch to put the IITs above MIT, Princeton, CMU, etc. - they are each good and bad in their own ways.

For the IIT Kanpur junta, someone else has also uploaded the musical production targetted at nostalgic alumni "Din Bhar" to Google Video. You must see this at least once.

QEMU on steroids
First there was QEMU that provided a fairly fast emulation of x86 hardware using a technique called "dynamic translation". Then came kqemu (or QEMU Accelerator Module) that allowed user code (ring 3) to run directly on the actual hardware providing speedups of around 3-5 times. Now comes the -kernel-kqemu option that allows even some of kernel code (ring 0) to run directly on the actual hardware providing impressive speedups over the old kqemu. Of course, these speedups come at the cost of affecting the stability of the host OS because of bugs in kqemu. kqemu is also not Free software, though it is free (gratis) for non-commercial uses.

In other news, GCC's SVN repository is also available for read-only access via HTTP for those who are stuck behind corporate firewalls and want access to the latest sources without having to download weekly snapshots. Of course, this is slower than the SVN protocol and might also be pulled off if it contributes too much to the load on the server.

"A look at GCJ 4.1"
Mark Wielaard has written another article for LWN.net titled "A look at GCJ 4.1" (where he also looks at GCJ 4.2 and beyond). It is subscribers-only for the moment (for a week), but if you are interested in Linux in any way, you should seriously consider subscribing to LWN. It's quite good.
ECJ for GCJ?
Tom proposed killing GCJX and replacing it with the Eclipse compiler for Java (Eclipse JDT Core plug-in, known informally as ECJ). He has been almost single-handedly working on GCJX for more than a year and it looks pretty good already, so it is pretty courageous of him to be the one to propose using something else instead of GCJX in the overall interests of GCJ.

ECJ seems pretty good and very actively maintained. It must be one of the fastest Java compilers around and fully supports the new language features introduced in JDK 1.5. So it is a very good move for GCJ.

Using ECJ does introduce GCC bootstrapping issues though. However, it should be possible to easily overcome these issues. The bigger issues are political and legal in nature. Let us hope these are resolved favourably.

I personally feel a little sad though. This removes another "fun" part of GCJ even though it is pragmatically a better thing to do, especially considering the precious little resources that the GCJ project has. I feel that GCJ is becoming more and more an "integration" project combining the best-of-breed in Free software for a given task - the Java language compiler would be ECJ, the garbage collector is Boehm-GC, the runtime library is GNU Classpath and the optmisation and code-generation is done by GCC. Of course, this can hardly be characterised as bad and is in fact quite a sensible thing to do given the limited amount of resources that the Free software world has at its disposal, but...

"Lisp is Sin"
Sriram Krishnan writes an interesting weblog entry on Lisp. As a side-effect, it made me read some of Peter Norvig's essays and mark his book "Paradigms of Artificial Intelligence Programming: Case Studies in Common Lisp" as well as Richard Gabriel's book "Patterns of Software: Tales from the Software Community" for later reading.
A Non-Invasive and Reversible Pre-processor for Java
I really like Per's implementation of a Java pre-processor.
rmathew.com
I have finally registered the domain rmathew.com for myself. It just points to my site hosted by Hosting Zero. The registration was surprisingly easy and rather quick. Within just a couple of minutes, the domain was accessible and the redirection was working. I chose GoDaddy.com even though they were more expensive for just the registration than Yahoo! because their private registration add-on turned out to be slightly cheaper on the whole than that of Yahoo! - I really do not want random people to access my personal information via a WHOIS lookup.

The "gotcha" about this registration turned out to be the fact that I inadvertently ended up with a pre-approved payment agreement with GoDaddy.com on my PayPal account, even though I had paid all the amount upfront and had marked my domain for manual renewal. Talking to their customer support didn't help much except stuff my mailbox with verbose and heavily graphic HTML messages. I have tried to contain the damage a bit by limiting the monthly outflow to USD 0.01, but I don't think I'll be sticking with them after my domain registration expires.

Profound Statement in Latin
Courtesy Anirban: "Quidquid Latine dictum sit, altum viditur" ("Whatever is said in Latin sounds profound").

Virtual Address Space Randomisation and Debugging
I feel rather silly today. Even though I knew about virtual address space randomisation in newer Linux kernels, it never struck me that I should disable it to get a reproducible debugging session with predictable breakpoint conditionals. My silly workaround was to use this patch:
Index: tree-ssa-operands.c
===================================================================
--- tree-ssa-operands.c (revision 109196)
+++ tree-ssa-operands.c (working copy)
@@ -1460,6 +1460,16 @@ get_call_expr_operands (tree stmt, tree
   tree op;
   int call_flags = call_expr_flags (expr);

+ if (strcmp (lang_hooks.decl_printable_name (current_function_decl, 2), + "of") == 0) + { + const char *called_f + = lang_hooks.decl_printable_name (TREE_OPERAND (TREE_OPERAND (stmt, 0), + 0), 2); + if (strcmp (called_f, "_Jv_ThrowBadArrayIndex") == 0) + printf ("Hello \"_Jv_ThrowBadArrayIndex\"!\n"); + } + if (!bitmap_empty_p (call_clobbered_vars)) { /* A 'pure' or a 'const' functions never call clobber anything.

and then put a breakpoint at the "printf" to get the debugger to stop the compiler process while processing the operands for the statement I was interested in.

Thanks to Mike Stump, we now have a page in the GCC Wiki that explains this problem and how to avoid it. Putting in the desired breakpoint is very simple now and avoids unnecessarily kludgy patches that contaminate the tree:

(gdb) b tree-ssa-operands.c:1463
Breakpoint 1 at 0x80d1f3f: file /extra/src/gcjx/gcc/gcc/tree-ssa-operands.c, line 1463.
(gdb) cond 1 stmt==0xb7c27fc8
Cool! Now all that is left is to use this breakpoint to figure out what the actual problem is that caused us to fire up a debugger.
Confessions of a TAB-hater
I do not like it when people put TAB characters in their source code for indentation. I prefer to use spaces instead of TAB characters to indent my source code. Jamie Zawinski has written a nice document that clearly explains the problem. Note that I am not against using the Tab key as a quick way of indenting, but putting in actual TAB characters (ASCII character #9) in the source code. Different people set tabstops differently, so what looks good to them looks terrible to others. These characters also mess up the indentation in patch diffs.

VIM has an unfortunate optimisation that replaces consecutive spaces with as many TAB characters as possible and if you "set expandtab", then even desirable TAB characters (in Makefiles for example) are replaced by spaces. Yes, I know of using the Ctrl-V + Tab sequence to insert an actual TAB character in this mode, but it is painful. So I have ended up putting the following in my ".vimrc":

set shiftwidth=2
set tabstop=8
inoremap <Tab> <C-V><Tab>
autocmd BufNewFile,BufRead *.java setlocal expandtab
autocmd BufNewFile,BufRead *.c setlocal expandtab
autocmd BufNewFile,BufRead *.cc setlocal expandtab
autocmd BufNewFile,BufRead *.cpp setlocal expandtab
autocmd BufNewFile,BufRead *.h setlocal expandtab
autocmd BufNewFile,BufRead *.hh setlocal expandtab
autocmd BufNewFile,BufRead *.hpp setlocal expandtab
autocmd BufNewFile,BufRead *.xml setlocal expandtab
autocmd BufNewFile,BufRead *.sql setlocal expandtab
If I were to design a programming language, I would seriously consider not allowing TAB characters to be counted as whitespace. It would make source code use up a few extra bytes compared to what it would if consecutive spaces are replaced by as many TAB characters as possible, but I would trade that off for overall sanity.

By the way, I consider it really silly that the authors of make chose to make TAB characters so important, when they are virtually indistuingishable from spaces when you inspect Makefiles. Their mistake has cost the software world the creation of the monstrosity named Ant.

The Etymology of "Foo"
RFC 3092 is devoted to explaining how "foobar" came to be used so much in software code and documentation.

"A Practical Sanskrit Introductory"
Thanks to Anirban Mukherjee, I came across a nice document (2.5MB PDF) written by Charles Wikner containing introductory lessons for the Sanskrit language. Just take a look at the first chapter to see why I personally consider the phonetically precise Devanagari script to be far superior than the utterly challenged and much abused Roman script, even at the risk of appearing jingoistic.

Twenty Years of comp.compilers
comp.compilers has turned twenty. It is one of the few USENET newsgroups that I try to read regularly and whose moderator John R. Levine has done a rather fine job over the years of keeping the signal-to-noise ratio high enough. He is also known to put in editorial remarks, almost always at the end, in many a post that either answer a question outright or contain pointers to useful material or contain quirky and mostly amusing remarks. Kudos to him and the community that sustains this awesome resource.

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