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# Best Abuse of CPP
Daniel Vik
926 Genter Street
La Jolla, Ca 92037
US
http://www.vik.cc/
Daniel Vik
US
<https://www.vik.cc/>
<http://www.danielvik.com>
## To build:
@@ -27,174 +25,194 @@ echo "Do or do not. There is no try."
## Judges' remarks:
The fun thing about CPP abuses is that, in most cases, running the
preprocessor on them doesn't help you decipher the obfuscated code.
That's assuming your preprocessor can take it at all.
The fun thing about [CPP](https://en.wikipedia.org/wiki/C_preprocessor) abuses
is that, in most cases, running the
[preprocessor](https://en.wikipedia.org/wiki/C_preprocessor) on them doesn't
help you decipher the obfuscated code. That's assuming your preprocessor can
take it at all.
## Author's remarks:
### Introduction
It's been a while since the last pre-processor killer won the ioccc.
I thought it was time to relive hour long compile times so I made a
program that does (almost) all computation in the pre-processor. The
program even causes gcc (and other pre-processors) to crash when
configured to do maximum number of computations.
The default configuration of the makefile is set to make the program
compile in a not too long time.
It's been a while since the last
[pre-processor](https://en.wikipedia.org/wiki/C_preprocessor) killer won the
IOCCC. I thought it was time to relive hour long compile times so I made a
program that does (almost) all computation in the pre-processor. The program
even causes `gcc` (and other pre-processors) to crash when configured to do
maximum number of computations. The default configuration of the
[Makefile](Makefile) is set to make the program compile in a not too long time.
I've got cpp to crash in a couple of diffenent ways. Most common is to
get a segmentation fault, but a couple of times it just got stuck in
I've got `cpp` to crash in a couple of different ways. Most common is to
get a segmentation fault, but a couple of times it just got stuck in
some infinite loop.
I actually had to write my own pre-processor to verify that the program
was doing the right thing...
I actually had to write my own
[pre-processor](https://en.wikipedia.org/wiki/C_preprocessor) to verify that the
program was doing the right thing...
Since it takes a very long time to compile the program, there is a
symbol that can be defined to shorten the compile time and avoid
Since it takes a very long time to compile the program, there is a
symbol that can be defined to shorten the compile time and avoid
compiler errors.
### Features
The program implements an 11-bit ALU in the pre-processor. The ALU has
two registers, X and Y, for calculations and one status register SR.
Each bit in the registers are represented by one symbol that are either
defined or undefined.
The program implements an 11-bit
[ALU](https://en.wikipedia.org/wiki/Arithmetic_logic_unit) in the
[pre-processor](https://en.wikipedia.org/wiki/C_preprocessor). The ALU has two
[registers](https://en.wikipedia.org/wiki/Processor_register), `X` and `Y`, for
calculations and one status register `SR`. Each bit in the registers are
represented by one symbol that are either defined or undefined.
The ALU has six instructions:
The ALU has six instructions:
CLR_X - Clear register X
- `CLR_X` - Clear [register](https://en.wikipedia.org/wiki/Processor_register) `X`.
CLR_Y - Clear register Y
- `CLR_Y` - Clear [register](https://en.wikipedia.org/wiki/Processor_register) `Y`.
ADD - Calculates X + Y and stores the result in X. If the result
is larger than 11 bits, the CARRY bit in SR is set otherwise
the CARRY bit is cleared.
- `ADD` - Calculates `X` + `Y` and stores the result in `X`. If the result
is larger than 11 bits, the [CARRY
bit](https://en.wikipedia.org/wiki/Carry_flag) in `SR` is set otherwise
the `CARRY` bit is cleared.
SUB - Calculates X - Y and stores the result in X. If Y was larger
than X, the CARRY bit in SR is set otherwise the CARRY bit
is cleared.
- `SUB` - Calculates `X` - `Y` and stores the result in `X`. If `Y` was larger
than `X`, the [CARRY bit](https://en.wikipedia.org/wiki/Carry_flag)
in `SR` is set otherwise the `CARRY` bit is cleared.
TST - If X == Y the EQ bit in SR is set, otherwise the EQ bit is
cleared. If X < Y the LT bit in SR is set, othervise the LT
- `TST` - If `X` == `Y` the `EQ` bit in `SR` is set, otherwise the `EQ` bit is
cleared. If `X` < `Y` the `LT` bit in `SR` is set, otherwise the `LT`
bit is cleared.
INC2 - Calculates X + 2 and stores the result in X. The CARRY bit
is handled as in the ADD instruction.
- `INC2` - Calculates `X` + 2 and stores the result in `X`. The [CARRY
bit](https://en.wikipedia.org/wiki/Carry_flag) is handled as in the
`ADD` instruction.
Internally the ALU implements a one bit adder with a carry in and carry
out. This adder is the core of the ALU. The ADD instruction uses the one
bit adder to create the 11-bit adder. The SUB instruction is implemented
by adding ~Y to X and then add 1. Finally the TST instruction calculates
X-Y and checks the result and the CARRY bit in the SR register to set
the EQ and LT bits.
Internally the [ALU](https://en.wikipedia.org/wiki/Arithmetic_logic_unit)
implements a one bit adder with a carry in and carry out. This adder is the core
of the ALU. The `ADD` instruction uses the one bit adder to create the 11-bit
adder. The SUB instruction is implemented by adding `~Y` to `X` and then add 1.
Finally the `TST` instruction calculates `X-Y` and checks the result and the
[CARRY bit](https://en.wikipedia.org/wiki/Carry_flag) in the `SR`
[register](https://en.wikipedia.org/wiki/Processor_register) to set the `EQ` and
`LT` bits.
All calculations are made using only the #ifdef, #infdef, #else, #endif,
#define and #undef. I never assign a value to a defined symbol. The
logic is done by assuming that a defined symbol is 1 and an undefined
All calculations are made using only `#ifdef`, `#ifndef`, `#else`, `#endif`,
`#define` and `#undef`. I never assign a value to a defined symbol. The
logic is done by assuming that a defined symbol is 1 and an undefined
symbol is 0. (I guess this means that I have unlimited memory as long as
I only store zeroes (!)).
The application that uses the pre-processor ALU is a prime number
generator. The application uses the same pre-processor directives.
Needed variables are stored in memory represended by one defined or
undefined symbol per bit. When doing arithmetics, the variables are
loaded into the X and Y registers by defining / undefining the X and Y
register bits. Then the calcualtion is made and the result is moved back
to the memory.
The application that uses the
[pre-processor](https://en.wikipedia.org/wiki/C_preprocessor)
[ALU](https://en.wikipedia.org/wiki/Arithmetic_logic_unit) is a [prime
number](https://en.wikipedia.org/wiki/Prime_number)
generator. The application uses the same pre-processor directives.
Needed variables are stored in memory represented by one defined or
undefined symbol per bit. When doing arithmetics, the variables are
loaded into the `X` and `Y` registers by defining / undefining the `X` and `Y`
[register](https://en.wikipedia.org/wiki/Processor_register) bits. Then the
calculation is made and the result is moved back to the memory.
The choice of application may be a bit unfortunate since we've already
seen a winning entry calculating prime nubmers in the pre-processor.
There is a big difference though. The 1988 applin entry uses pre-
processor arithmethic (in a very nice way though). This program only
defines and undefines symbols in a well defined ;) way and doesn't do
The choice of application may be a bit unfortunate since we've already
seen a winning entry calculating [prime
numbers](https://en.wikipedia.org/wiki/Prime_number) in the
[pre-processor](https://en.wikipedia.org/wiki/C_preprocessor).
There is a big difference though. The 1988 applin entry uses pre-
processor arithmetic (in a very nice way though). This program only
defines and undefines symbols in a well defined ;) way and doesn't do
any pre-processor arithmetics.
The reason why I choosed to do a prime number application is that the
algorithm can be written to do a lot of calculations without a lot of
nesting (gnu cpp allows only 200 nested includes).
The reason why I chose to do a [prime
number](https://en.wikipedia.org/wiki/Prime_number) application is that the
algorithm can be written to do a lot of calculations without a lot of nesting
(`gnu cpp` allows only 200 nested includes).
### Build and Run
First, do a first pre processing of the initial definitions. The FNAME
symbol must be defined to the name of the output file. If you want to
speed up the compilation, define the STOP symbol to anything from _3 to
_10. (The default value is _10 which will make the compilation take some
time.) Prime numbers up to 2^STOP will be calculated.
First, do a first pre-processing of the initial definitions. The FNAME
symbol must be defined to the name of the output file. If you want to
speed up the compilation, define the `STOP` symbol to anything from `_3` to
`_10`. (The default value is `_10` which will make the compilation take some
time.) Prime numbers up to `2^STOP` will be calculated.
```sh
cpp '-DSTOP=_5' '-DFNAME="tmp1.c"' prog.c tmp1.c
```
Then use cpp or any other pre-processor to do the actual work. This will
take some time....
Then use `cpp` or any other
[pre-processor](https://en.wikipedia.org/wiki/C_preprocessor) to do the actual
work. This will take some time....
```sh
cpp tmp1.c > tmp2.c
```
Finally compile the pre processed file
Finally compile the pre-processed file
```sh
cc -O tmp2.c -o prog
```
Then run the program to reveil all prime numbers up to 32 (if you used
STOP=_5 as above):
Then run the program to reveal all prime numbers up to 32 (if you used
`STOP=_5` as above):
```sh
./prog
./vik2
```
### Verification
I wasn't able to compile the full program which calculates prime numbers
up to 1024 using gnu cpp (or any other pre-processor) so I had to write
my own. Knowing how the program works it was quite easy to reduce the
compilation time from several hours to about one second. I also added
some statistics to my home made pre-processor and I found that
calculating prime numbers up to 1024 makes the program include itself
over 6.8 million times (see the statistics table below).
I wasn't able to compile the full program which calculates [prime
numbers](https://en.wikipedia.org/wiki/Prime_number) up to 1024 using `gnu cpp`
(or any other [pre-processor](https://en.wikipedia.org/wiki/C_preprocessor)) so
I had to write my own. Knowing how the program works it was quite easy to reduce
the compilation time from several hours to about one second. I also added some
statistics to my home made pre-processor and I found that calculating prime
numbers up to 1024 makes the program include itself over 6.8 million times (see
the statistics table below).
### Obfuscation
Well, since 98.5% of the program is preprocessor directives, the main
obfuscation is the use of preprocessor directives.
Well, since 98.5% of the program is
[preprocessor](https://en.wikipedia.org/wiki/C_preprocessor) directives, the
main obfuscation is the use of preprocessor directives.
Doing arithmetics without acutally using any arithmetic operations makes
Doing arithmetics without actually using any arithmetic operations makes
the program quite hard to follow.
In order to actually do the calculations, the program includes itself a
In order to actually do the calculations, the program includes itself a
lot.
The symbol names are made as short as possible to meet the space limits.
This of course adds to the obfuscation (even though the program is
This of course adds to the obfuscation (even though the program is
quite obfuscated with longer, readable macro names.
Finally, I made the 1.5% c code a bit harder to read by breaking all
Finally, I made the 1.5% C code a bit harder to read by breaking all
lines after three characters.
The program has 1029 lines which makes it the longest entry (so far).
Even though the pre-processed and indented output is easier to read, it
Even though the pre-processed and indented output is easier to read, it
is quite hard to find the code in it. The size of the pre-processed file
is several Mb when using gnu cpp.
is several Mb when using `gnu cpp`.
### Limitations
In order to fit the program within the space limits, I had to define the
#define, #endif, and some other directives as single character symbols.
This does not compile on all pre-processors but using gnu cpp as a first
compilation step solves this.
`#define`, `#endif`, and some other directives as single character symbols.
This does not compile on all
[pre-processors](https://en.wikipedia.org/wiki/C_preprocessor) but using `gnu
cpp` as a first compilation step solves this.
### Statistics
The table below contains some interesting statistics about the
compilation of the program. The intermediate file size is the size of
the output file of the cpp pre-processor. The time taken to pre process
the program were measured using gnu cpp on my 2.0MHz P4 with 512Mb ram
and a lot of disk.
The table below contains some interesting statistics about the compilation of
the program. The intermediate file size is the size of the output file of the
cpp [pre-processor](https://en.wikipedia.org/wiki/C_preprocessor). The time
taken to pre-process the program were measured using gnu cpp on my 2.0MHz P4
with 512Mb ram and a lot of disk.
```
Generated Recursive Max nest Intermediate
Level prime nrs includes count file size Time
@@ -208,6 +226,7 @@ and a lot of disk.
_10 < 1024 6 826 389 114 63 782 912(*) 2h 47'58"(*)
(*) Before cpp crashed.
```
## Copyright and CC BY-SA 4.0 License: