Find limit of recursion

Find limit of recursion
You are encouraged to solve this task according to the task description, using any language you may know.

Find limit of recursion is part of Short Circuit's Console Program Basics selection.

Find the limit of recursion.

Batch File

MUNG.CMD is a commandline tool written in DOS Batch language. It finds the limit of recursion possible using CMD /C.

<lang dos>@echo off set /a c=c+1 echo [Depth %c%] Mung until no good cmd /c mung.cmd echo [Depth %c%] No good set /a c=c-1</lang>

Result (abbreviated):

...
[Depth 259] Mung until no good
[Depth 260] Mung until no good
[Depth 261] Mung until no good
[Depth 261] No good
[Depth 260] No good
[Depth 259] No good
...

If one uses call rather than CMD/C, the call depth is much deeper but ends abruptly and can't be trapped.

<lang dos>@echo off set /a c=c+1 echo [Depth %c%] Mung until no good call mung.cmd echo [Depth %c%] No good set /a c=c-1</lang>

Result (abbreviated):

1240: Mung until no good
1241: Mung until no good
******  B A T C H   R E C U R S I O N  exceeds STACK limits ******
Recursion Count=1240, Stack Usage=90 percent
******       B A T C H   PROCESSING IS   A B O R T E D      ******

You also get the exact same results when calling mung internally, as below

<lang dos>@echo off set c=0

mung

set /a c=c+1 echo [Level %c%] Mung until no good call :mung set /a c=c-1 echo [Level %c%] No good</lang>

Setting a limit on the recursion depth can be done like this:

<lang dos>@echo off set c=0

mung

set /a c=%1+1 if %c%==10 goto :eof echo [Level %c%] Mung until no good call :mung %c% set /a c=%1-1 echo [Level %c%] No good</lang>

C

<lang c>#include <stdio.h>

void recurse(unsigned int i) {

 printf("%d\n", i);
 recurse(i+1); // 523756

}

int main() {

 recurse(0);
 return 0;

}</lang>

Segmentation fault occurs when i is 523756. (This was checked debugging with gdb rather than waiting the output: the printf line for the test was commented). It must be noted that the recursion limit depends on how many parameters are passed onto the stack. E.g. adding a fake double argument to recurse, the limit is reached at i == 261803. The limit depends on the stack size and usage in the function. Even if there are no arguments, the return address for a call to a subroutine is stored on the stack (at least on x86 and many more processors), so this is consumed even if we put arguments into registers.

Python

<lang python>import sys print sys.getrecursionlimit()</lang>

Tcl

<lang tcl>proc recur i {

   puts "This is depth [incr i]"
   catch {recur $i}; # Trap error from going too deep

} recur 0</lang> The tail of the execution trace looks like this:

This is depth 995
This is depth 996
This is depth 997
This is depth 998
This is depth 999

Note that the maximum recursion depth is a tunable parameter, as is shown in this program: <lang tcl># Increase the maximum depth interp recursionlimit {} 1000000 proc recur i {

   if {[catch {recur [incr i]}]} {
       # If we failed to recurse, print how far we got

puts "Got to depth $i"

   }

} recur 0</lang> For Tcl 8.5 on this platform, this prints:

Got to depth 6610

At which point it has exhausted the C stack. Tcl 8.6 uses a stackless execution engine, and can go very deep if required:

Got to depth 999999

VBScript

Haven't figured out how to see the depth. And this depth is that of calling the O/S rather than calling within.

<lang vb>'mung.vbs option explicit

dim c if wscript.arguments.count = 1 then c = wscript.arguments(0) c = c + 1 else c = 0 end if wscript.echo "[Depth",c & "] Mung until no good." CreateObject("WScript.Shell").Run "cscript Mung.vbs " & c, 1, true wscript.echo "[Depth",c & "] no good."</lang>

Okay, the internal limits version.

<lang vb>'mung.vbs option explicit

sub mung(c) dim n n=c+1 wscript.echo "[Level",n & "] Mung until no good" on error resume next mung n on error goto 0 wscript.echo "[Level",n & "] no good" end sub

mung 0</lang>

Output (abbrev.):

[Level 1719] Mung until no good
[Level 1720] Mung until no good
[Level 1721] Mung until no good
[Level 1722] Mung until no good
[Level 1722] no good
[Level 1721] no good
[Level 1720] no good
[Level 1719] no good