Best Abuse of the C Preprocessor

Cプリプロセッサの最高の悪用

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#include <stdio.h>

#define d define

#d b12(x) 12 x
#d a13(x) x 13
#d a16(x) x 16
#d a32(x) x 32
#d acb(x) x]
#d acc(x) x}
#d aco(x) x:
#d bco(x) :x
#d acp(x) x)
#d bef(x) EOF x
#d aeq(x) x=
#d afo(x) x for
#d age(x) x fgetc
#d asi(x) x stdin
#d aso(x) x stdout
#d bgt(x) >x
#d ai(x) x i
#d aj(x) x j
#d al(x) x l
#d ami(x) x-
#d bne(x) !=x
#d aob(x) x[
#d aop(x) x(
#d apl(x) x+
#d bpu(x) fputc x
#d bqm(x) ?x
#d aqm(x) x?
#d aqu(x) x'
#d ase(x) x;
#d awh(x) x while
#d axo(x) x^
#d a0(x) x 0
#d b13(x) 13 x
#d b16(x) 16 x
#d b19(x) 19 x
#d b48(x) 48 x
#d a64(x) x 64
#d b66(x) 66 x
#d bcb(x) ]x
#d bch(x) char x
#d bcm(x) ,x
#d acm(x) x,
#d bcp(x) )x
#d beq(x) =x
#d bex(x) extern x
#d bi(x) i x
#d bin(x) int x
#d bix(x) index x
#d bj(x) j x
#d bl(x) l x
#d alt(x) x<
#d bma(x) main x
#d bob(x) [x
#d boc(x) {x
#d bop(x) (x
#d bpl(x) +x
#d app(x) x++
#d bqu(x) 'x
#d bse(x) ;x
#d bst(x) *x
 
bma(acp(bop(app(bcp(ai(boc(ase(bch(a16(bl(alt(bob(ai(b66(ase(bcb(a0(bcm(aeq(bst(acb(bj(a64(bse(aob(bin(al(bi(aeq(bse(ai(bex(aop(bch(afo(bst(ase(bix(())))))))))))))))))))))))))))))))))))))))
bl(ai(bob(aob(bi(al(bcb(aop(beq(apl(b13(a13(bpl(aeq(bop(acb(bl(bob(a32(bi(bpl(apl(b16(bcb(ai(beq(b19(aob(bpl(bop(l))))))))))))))))))))))))))))))
bpl(acp(b48(acp(asi(bcb(aop(beq(age(bop(aeq(bi(ai(bgt(aop(b12(aop(bqm(awh(b12(ase(bco(acp(bi(acp(bcp(acp(bpl(aqu(bqu(A))))))))))))))))))))))))))))))
bne(acc(bef(ase(bcp(acp(aso(bpu(acm(ai(bop(aco(bop(acb(bj(al(beq(ami(bix(aj(axo(bop(a16(aob(bl(al(aqm(bcm(acp(acp(i))))))))))))))))))))))))))))))

引用元：https://www.ioccc.org/1990/dg.c

審査員・作者による説明：https://github.com/ioccc-src/winner/blob/main/1990/dg.hint

動作

ROT13エンコーダ。

$ gcc -o dg dg.c

$ echo Hello | ./dg
Uryyb

解説

トークンを1つだけ追加するマクロを大量に定義し、それらを組み合わせるだけでプログラムを構成している。単純だがおもしろい。

#define aqu(x) x'
#define bqu(x) 'x

aqu(bpu(A))

によって'A'を作り出す、というのは動かないので、これは'A'に置き換えた（このことはdg.hintにも書かれている）。また、#define d defineのトリックも動かないので書き下した。

パッチ

--- dg.c
+++ dg.c
@@ -2,68 +2,68 @@
 
 #define d define
 
-#d b12(x) 12 x
-#d a13(x) x 13
-#d a16(x) x 16
-#d a32(x) x 32
-#d acb(x) x]
-#d acc(x) x}
-#d aco(x) x:
-#d bco(x) :x
-#d acp(x) x)
-#d bef(x) EOF x
-#d aeq(x) x=
-#d afo(x) x for
-#d age(x) x fgetc
-#d asi(x) x stdin
-#d aso(x) x stdout
-#d bgt(x) >x
-#d ai(x) x i
-#d aj(x) x j
-#d al(x) x l
-#d ami(x) x-
-#d bne(x) !=x
-#d aob(x) x[
-#d aop(x) x(
-#d apl(x) x+
-#d bpu(x) fputc x
-#d bqm(x) ?x
-#d aqm(x) x?
-#d aqu(x) x'
-#d ase(x) x;
-#d awh(x) x while
-#d axo(x) x^
-#d a0(x) x 0
-#d b13(x) 13 x
-#d b16(x) 16 x
-#d b19(x) 19 x
-#d b48(x) 48 x
-#d a64(x) x 64
-#d b66(x) 66 x
-#d bcb(x) ]x
-#d bch(x) char x
-#d bcm(x) ,x
-#d acm(x) x,
-#d bcp(x) )x
-#d beq(x) =x
-#d bex(x) extern x
-#d bi(x) i x
-#d bin(x) int x
-#d bix(x) index x
-#d bj(x) j x
-#d bl(x) l x
-#d alt(x) x<
-#d bma(x) main x
-#d bob(x) [x
-#d boc(x) {x
-#d bop(x) (x
-#d bpl(x) +x
-#d app(x) x++
-#d bqu(x) 'x
-#d bse(x) ;x
-#d bst(x) *x
+#define b12(x) 12 x
+#define a13(x) x 13
+#define a16(x) x 16
+#define a32(x) x 32
+#define acb(x) x]
+#define acc(x) x}
+#define aco(x) x:
+#define bco(x) :x
+#define acp(x) x)
+#define bef(x) EOF x
+#define aeq(x) x=
+#define afo(x) x for
+#define age(x) x fgetc
+#define asi(x) x stdin
+#define aso(x) x stdout
+#define bgt(x) >x
+#define ai(x) x i
+#define aj(x) x j
+#define al(x) x l
+#define ami(x) x-
+#define bne(x) !=x
+#define aob(x) x[
+#define aop(x) x(
+#define apl(x) x+
+#define bpu(x) fputc x
+#define bqm(x) ?x
+#define aqm(x) x?
+#define aqu(x) x'
+#define ase(x) x;
+#define awh(x) x while
+#define axo(x) x^
+#define a0(x) x 0
+#define b13(x) 13 x
+#define b16(x) 16 x
+#define b19(x) 19 x
+#define b48(x) 48 x
+#define a64(x) x 64
+#define b66(x) 66 x
+#define bcb(x) ]x
+#define bch(x) char x
+#define bcm(x) ,x
+#define acm(x) x,
+#define bcp(x) )x
+#define beq(x) =x
+#define bex(x) extern x
+#define bi(x) i x
+#define bin(x) int x
+#define bix(x) index x
+#define bj(x) j x
+#define bl(x) l x
+#define alt(x) x<
+#define bma(x) main x
+#define bob(x) [x
+#define boc(x) {x
+#define bop(x) (x
+#define bpl(x) +x
+#define app(x) x++
+#define bqu(x) 'x
+#define bse(x) ;x
+#define bst(x) *x
  
 bma(acp(bop(app(bcp(ai(boc(ase(bch(a16(bl(alt(bob(ai(b66(ase(bcb(a0(bcm(aeq(bst(acb(bj(a64(bse(aob(bin(al(bi(aeq(bse(ai(bex(aop(bch(afo(bst(ase(bix(())))))))))))))))))))))))))))))))))))))))
 bl(ai(bob(aob(bi(al(bcb(aop(beq(apl(b13(a13(bpl(aeq(bop(acb(bl(bob(a32(bi(bpl(apl(b16(bcb(ai(beq(b19(aob(bpl(bop(l))))))))))))))))))))))))))))))
-bpl(acp(b48(acp(asi(bcb(aop(beq(age(bop(aeq(bi(ai(bgt(aop(b12(aop(bqm(awh(b12(ase(bco(acp(bi(acp(bcp(acp(bpl(aqu(bqu(A))))))))))))))))))))))))))))))
+bpl(acp(b48(acp(asi(bcb(aop(beq(age(bop(aeq(bi(ai(bgt(aop(b12(aop(bqm(awh(b12(ase(bco(acp(bi(acp(bcp(acp(bpl('A'))))))))))))))))))))))))))))
 bne(acc(bef(ase(bcp(acp(aso(bpu(acm(ai(bop(aco(bop(acb(bj(al(beq(ami(bix(aj(axo(bop(a16(aob(bl(al(aqm(bcm(acp(acp(i))))))))))))))))))))))))))))))

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