language in favor of much more obscure ways of achieving the same thing. Contributions have included source code formatted to resemble images, text, etc., after the manner of ASCII art, preprocessor redefinitions to make code harder to read, and self-modifying code. In several years, an entry was submitted that required a new definition of some of the rules for the next year. This is regarded as a high honor. An example is the world's shortest self-reproducing program. The entry was a program designed to output its own source code, and which had zero bytes of source code. When the program ran, it printed out zero bytes, equivalent to its source code. In the effort to take obfuscation to its extremes, contestants have produced programs which skirt around the edges of C standards, or result in constructs which trigger rarely used code path combinations in compilers. As a result, several of the past entries may not compile directly in a modern compiler, and some may cause crashes. Examples Within the code size limit of only a few kilobytes, contestants have managed to do complicated things – a 2004 winner turned out an operating system. Toledo NanochessToledo Nanochess is a chess engine created by Mexican software developer Oscar Toledo Gutiérrez, a five-time winner of the IOCCC. In accordance with IOCCC rules, it is 1255 characters long. The author claims that it is the world's smallest chess program written in C. The source code for Toledo Nanochess and other engines is available. Because Toledo Nanochess is based on Toledo's winning entry from the 18th IOCCC (Best Game), it is heavily obfuscated. On February 2, 2014, the author published the book Toledo Nanochess: The commented source code, which contains the fully commented source code. As of February 7, 2010, it appears to be one of only two chess engines written in less than 2 kilobytes of C that are able to play full legal chess moves, along with Micro-Max by Dutch physicist H. G. Muller. In 2014 the 1 kilobyte barrier was broken by Super Micro Chess – a derivative of Micro-Max – totaling 760 characters (spaces and newlines included). There is also a smaller version of Toledo's engine, the Toledo Picochess, consisting of 944 non-blank characters. Source code excerpt B,i,y,u,b,I[411],*G=I,x=10,z=15,M=1e4;X(w,c,h,e,S,s){int t,o,L,E,d,O=e,N=-M*M,K =78-h<<x,p,*g,n,*m,A,q,r,C,J,a=y?-x:x;y^=8;G++;d=w||s&&s>=h&&v 0,0)>M;do{_ o=I[ p=O]){q=o&z^y _ q<7){A=q--&2?8:4;C=o-9&z?q["& .$ "]:42;do{r=I[p+=C[l]-64]_!w|p ==w){g=q|p+a-S?0:I+S _!r&(q|A<3||g)||(r+1&z^y)>9&&q|A>2){_ m=!(r-2&7))P G[1]=O, K;J=n=o&z;E=I[p-a]&z;t=q|E-7?n:(n+=2,6^y);Z n<=t){L=r?l[r&7]*9-189-h-q:0 _ s)L +=(1-q?l[p/x+5]-l[O/x+5]+l[p%x+6]*-~!q-l[O%x+6]+o/16*8:!!m*9)+(q?0:!(I[p-1]^n)+ !(I[p+1]^n)+l[n&7]*9-386+!!g*99+(A<2))+!(E^y^9)_ s>h||1<s&s==h&&L>z|d){p[I]=n,O [I]=m?*g=*m,*m=0:g?*g=0:0;L-=X(s>h|d?0:p,L-N,h+1,G[1],J=q|A>1?0:p,s)_!(h||s-1|B -O|i-n|p-b|L<-M))P y^=8,u=J;J=q-1|A<7||m||!s|d|r|o<z||v