On: Xmas.c (1988)

[theideaofcoffee]

This particular entry to the IOCCC was for 1988, those two algorithms didn’t come about for a few more years after that, gzip in the early nineties and 7z later that decade. The note is probably correct when comparing against the state of the art at the time.

[acqq → theideaofcoffee]

You are right. Here is the source of "compress" that existed at that time. It compresses the produced song to 1048 bytes, not less.

https://www.nic.funet.fi/index/minix/compress.c

The program that produces the song, without the introductory comment, is 913 bytes, as presented in the article. Removing whitespaces it uses just 800 bytes and produces the song which is 2359 chars here. The whole C is:

    main(t,_,a)char*a;{return!0<t?t<3?main(-79,-13,a+main(-87,1-_,
    main(-86,0,a+1)+a)):1,t<_?main(t+1,_,a):3,main(-94,-27+t,a)&&t==
    2?_<13?main(2,_+1,"%s%d%d\n"):9:16:t<0?t<-72?main(_,t,
    "@n'+,#'/*{}w+/w#cdnr/+,{}r/*de}+,/*{*+,/w{%+,/w#q#n+,/#{l,+,/n{n+,/+#n+,/#;\
    #q#n+,/+k#;*+,/'r :'d*'3,}{w+K w'K:'+}e#';dq#'l q#'+d'K#!/+k#;\
    q#'r}eKK#}w'r}eKK{nl]'/#;#q#n'){)#}w'){){nl]'/+#n';d}rw' i;# ){nl]!/n{n#'; \
    r{#w'r nc{nl]'/#{l,+'K {rw' iK{;[{nl]'/w#q#\
    \
    n'wk nw' iwk{KK{nl]!/w{%'l##w#' i; :{nl]'/*{q#'ld;r'}{nlwb!/*de}'c ;;\
    {nl'-{}rw]'/+,}##'*}#nc,',#nw]'/+kd'+e}+;\
    #'rdq#w! nr'/ ') }+}{rl#'{n' ')# }'+}##(!!/")
    :t<-50?_==*a?putchar(31[a]):main(-65,_,a+1):main((*a=='/')+t,_,a+1):
    0<t?main(2,2,"%s"):*a=='/'||main(0,main(-61,*a,
    "!ek;dc i@bK'(q)-[w]*%n+r3#l,{}:\nuwloca-O;m .vpbks,fxntdCeghiry"),a+1);}

It compiles and links even without #include.

[sdkgames → theideaofcoffee]

gzip is based on the DEFLATE algorithm, which is a combination of LZ77(1977) and Huffman coding(1952).( https://en.wikipedia.org/wiki/Gzip )

[1986 → sdkgames]

DEFLATE was created / implemented / speced / whatever word you want to apply by Phil Katz no earlier than 1989

[arp242 → sdkgames]

"Based on" is not the same as "identical".