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Code Overview
This function is meant to decide, for a given input $n$,
whether $n$ is divisible by 3 or not. So we expect the
overall program to look somewhat like this:
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< the program > ≡
/* Test program, (c) 2013 The Author */
< header file inclusion >
< test function >
#define THIS_IS_AN_ENORMOUSLY_LONG_SYMBOLIC_CONSTANT_NAME 42
main () {
int x;
printf ("Enter number"); // show message
input (x); // read number
if (testdiv3(x)) {
printf ("%d is divisible by 3.\n", x);
} else {
printf ("%d is not divisible by 3.\n", x);
}
return;
}
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We will certainly need to include some header files because
we want to use the printf and input functions:
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< header file inclusion > ≡
#include // for printf()
#include "../myread.h" // for input()
// This has nothing to do with headers, but
// this way you can see a really long line
#define YET_ANOTHER_SYMBOLIC_CONSTANT_WHICH_HAS_A_LONG_NAME_ONLY_THIS_TIME_IT_IS_SO_LONG_THAT_IT_WILL_SPAN_SEVERAL_LINES_IN_THE_OUTPUT ((42+42)/42 + 40) // weird
typedef struct { /* this is also
something that */
int i; // int
int j; // more int
} /* does not belong here! */ useless_t;
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We could, of course, create a test function that
looks like the following one, testing for all possible
numbers which are divisible by 3---well, at least up
to some given maximum number. Of course, there are
infinitely many of them. So, what we're not going to
do is the following:
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< test function, bad one > ≡
int testdiv3(int x) {
return (
(x == 3) ||
(x == 6) ||
(x == 9) ||
(x == 12) ||
(x == 15) ||
(x == 18) ||
(x == 21) ||
(x == 24) ||
(x == 27) ||
(x == 30) ||
(x == 33) ||
(x == 36) ||
(x == 39) ||
(x == 42) ||
(x == 45) ||
(x == 48) ||
(x == 51) ||
(x == 54) ||
(x == 57) ||
(x == 60) ||
(x == 63) ||
(x == 66) ||
(x == 69) ||
(x == 72) ||
(x == 75) ||
(x == 78) ||
(x == 81) ||
(x == 84) ||
(x == 87) );
}
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Now, for some reason (and completely unrelated to the
task of this paper) we want to display the output
of ls -li---and it shall also appear on a slide.
We'll try it two times, once with side comments and
once just the code.
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< directory with comments > ≡
[esser@macbookpro:literate-teaching]$ LANG=C ls -li
total 288
15653128 drwxr-xr-x 5 esser staff 170 Apr 1 06:48 Literatur
15656814 drwxr-xr-x 4 esser staff 136 Apr 1 18:27 Software
15662900 -rwxr-xr-x 1 esser staff 7698 Apr 2 02:13 combine.py
15668192 -rwxr-xr-x 1 esser staff 4926 Apr 2 02:18 example.nw
15643259 -rwxr-xr-x 1 esser staff 6522 Apr 2 01:22 export.py
15658881 drwxr-xr-x 4 esser staff 136 Apr 1 17:44 fonts
15641951 -rw-r--r-- 1 esser staff 395 Mar 30 20:45 index.html
15661490 drwxr-xr-x 6 esser staff 204 Apr 1 19:40 logos
15667494 -rwxr-xr-x 1 esser staff 683 Apr 2 01:40 make.sh
15651837 -rw-r--r-- 1 esser staff 32418 Mar 31 22:35 nicEdit.js
15649904 -rw-r--r-- 1 esser staff 3351 Jun 7 2012 nicEditorIcons.gif
15643349 -rw-r--r-- 1 esser staff 12427 Apr 2 02:21 out.html
15660031 -rw-r--r-- 1 esser staff 17606 Apr 2 02:21 out2.html
15667034 -rw-r--r-- 1 esser staff 1141 Apr 2 02:21 result.txt
15658182 drwxr-xr-x 5 esser staff 170 Apr 1 17:21 s5-css
15662226 -rwxr-xr-x 1 esser staff 34312 Apr 2 00:24 sched-rr10.nw
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As promised, one more time:
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< directory without comments > ≡
[esser@macbookpro:literate-teaching]$ LANG=C ls -li
total 288
15653128 drwxr-xr-x 5 esser staff 170 Apr 1 06:48 Literatur
15656814 drwxr-xr-x 4 esser staff 136 Apr 1 18:27 Software
15662900 -rwxr-xr-x 1 esser staff 7698 Apr 2 02:13 combine.py
15668192 -rwxr-xr-x 1 esser staff 4926 Apr 2 02:18 example.nw
15643259 -rwxr-xr-x 1 esser staff 6522 Apr 2 01:22 export.py
15658881 drwxr-xr-x 4 esser staff 136 Apr 1 17:44 fonts
15641951 -rw-r--r-- 1 esser staff 395 Mar 30 20:45 index.html
15661490 drwxr-xr-x 6 esser staff 204 Apr 1 19:40 logos
15667494 -rwxr-xr-x 1 esser staff 683 Apr 2 01:40 make.sh
15651837 -rw-r--r-- 1 esser staff 32418 Mar 31 22:35 nicEdit.js
15649904 -rw-r--r-- 1 esser staff 3351 Jun 7 2012 nicEditorIcons.gif
15643349 -rw-r--r-- 1 esser staff 12427 Apr 2 02:21 out.html
15660031 -rw-r--r-- 1 esser staff 17606 Apr 2 02:21 out2.html
15667034 -rw-r--r-- 1 esser staff 1141 Apr 2 02:21 result.txt
15658182 drwxr-xr-x 5 esser staff 170 Apr 1 17:21 s5-css
15662226 -rwxr-xr-x 1 esser staff 34312 Apr 2 00:24 sched-rr10.nw
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By the way, the tool does know += and = for chunks:
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< header file inclusion > +≡
// watch above: this should be +=, not just =
#include "../somethingelse.h"
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And as a closing remark we present some very long source code which
is all in one chunk---we should not do that in reality of course. It
is just to show that the conversion tools can cope with it.
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< long code block > ≡
void syscall_waitpid (struct regs_syscall *r) {
// ebx: pid of child to wait for
// ecx: pointer to status
// edx: options (ignored)
int chpid = r->ebx;
int *status = (int*)r->ecx;
printf ("[%d] in syscall_waitpid, status (1) = 0x%x\n", current_task, status);
< imagine an even longer code block >
< imagine a code block which is yet longer >
printf ("[%d] waitpid: waiting for pid %d\n", current_task, chpid);
thread_table[current_task].state = TSTATE_WAITFOR; thread_table[current_task].waitfor = chpid;
remove_from_ready_queue (current_task);
add_to_blocked_queue (current_task, &waitpid_queue);
printf ("[%d] waitpid: calling yield\n", current_task);
// syscall_yield (r); // here we yield
inside_yield = true;
scheduler (r, SCHED_SRC_WAITFOR);
/*
if (thread_table[current_task].state != TSTATE_WAITFOR) {
printf ("[%d] in syscall_waitpid: wrong return!\n", current_task);
return;
};
*/
// asm ("int $0x81"); // call scheduler
// PROBLEM
// We come back here after scheduler(), but with the memory and
// stack of a different thread. This is bad...
inside_yield = false;
printf ("waitpid: returned from yield (pid=%d)\n", current_task);
// now we've returned from syscall_yield, the child must have
// finished
// unblocking this process happens in syscall_exit() !
// remove_from_blocked_queue (current_task, &waitpid_queue);
// add_to_ready_queue (current_task);
// return value of waitpid is the process id of the terminated
// child. We expect that syscall_exit() has updated the waitfor
// field of the parent's TCB:
chpid = thread_table[current_task].waitfor;
if (chpid>0 && chpid
printf ("current_task = %d\n", current_task);
printf ("chpid = %d\n", chpid);
r->eax = chpid;
// the exitcode is in the child's exitcode field:
printf ("in syscall_waitpid, status (2) = 0x%x\n", status);
printf ("A...\n");
printf ("in syscall_waitpid. exitcode = %d\n", thread_table[chpid].exitcode);
printf ("B...\n");
*status = thread_table[chpid].exitcode;
printf ("in syscall_waitpid. *status = %d\n", *status);
// now remove child process
} else {
// *status = -1;
}
printf ("going to return from syscall_waitpid\n");
return;
}
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Resources
We used
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< credits > ≡
// credits:
// - S5, http://meyerweb.com/eric/tools/s5/
// - nicEdit, http://nicedit.com/
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