This is the original Malbolge interpreter

/* Interpreter for Malbolge. */
/* '98 Ben Olmstead. */
/* */
/* Malbolge is the name of Dante's Eighth circle of Hell. This */
/* interpreter isn't even Copylefted; I hereby place it in the public */
/* domain. Have fun... */
/* */
/* Note: in keeping with the idea that programming in Malbolge is */
/* meant to be hell, there is no debugger. */
/* */
/* By the way, this code assumes that short is 16 bits. I haven't */
/* seen any case where it isn't, but it might happen. If short is */
/* longer than 16 bits, it will still work, though it will take up */
/* considerably more memory. */
/* */
/* If you are compiling with a 16-bit Intel compiler, you will need */
/* >64K data arrays; this means using the HUGE memory model on most */
/* compilers, but MS C, as of 8.00, possibly earlier as well, allows */
/* you to specify a custom memory-model; the best model to choose in */
/* this case is /Ashd (near code, huge data), I think. */

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <malloc.h>
#include <string.h>

#ifdef __GNUC__
static inline
#endif
void exec( unsigned short *mem );

#ifdef __GNUC__
static inline
#endif
unsigned short op( unsigned short x, unsigned short y );

const char xlat1[] =
"+b(29e*j1VMEKLyC})8&m#~W>qxdRp0wkrUo[D7,XTcA\"lI"
".v%{gJh4G\\-=O@5`_3i<?Z';FNQuY]szf$!BS/|t:Pn6^Ha";

const char xlat2[] =
"5z]&gqtyfr$(we4{WP)H-Zn,[%\\3dL+Q;>U!pJS72FhOA1C"
"B6v^=I_0/8|jsb9m<.TVac`uY*MK'X~xDl}REokN:#?G\"i@";

int main( int argc, char **argv )
{
FILE *f;
unsigned short i = 0, j;
int x;
unsigned short *mem;
if ( argc != 2 )
{
fputs( "invalid command line\n", stderr );
return ( 1 );
}
if ( ( f = fopen( argv[1], "r" ) ) == NULL )
{
fputs( "can't open file\n", stderr );
return ( 1 );
}
#ifdef _MSC_VER
mem = (unsigned short *)_halloc( 59049, sizeof(unsigned short) );
#else
mem = (unsigned short *)malloc( sizeof(unsigned short) * 59049 );
#endif
if ( mem == NULL )
{
fclose( f );
fputs( "can't allocate memory\n", stderr );
return ( 1 );
}
while ( ( x = getc( f ) ) != EOF )
{
if ( isspace( x ) ) continue;
if ( x < 127 && x > 32 )
{
if ( strchr( "ji*p</vo", xlat1[( x - 33 + i ) % 94] ) == NULL )
{
fputs( "invalid character in source file\n", stderr );
free( mem );
fclose( f );
return ( 1 );
}
}
if ( i == 59049 )
{
fputs( "input file too long\n", stderr );
free( mem );
fclose( f );
return ( 1 );
}
mem[i++] = x;
}
fclose( f );
while ( i < 59049 ) mem[i] = op( mem[i - 1], mem[i - 2] ), i++;
exec( mem );
free( mem );
return ( 0 );
}

#ifdef __GNUC__
static inline
#endif
void exec( unsigned short *mem )
{
unsigned short a = 0, c = 0, d = 0;
int x;
for (;;)
{
if ( mem[c] < 33 || mem[c] > 126 ) continue;
switch ( xlat1[( mem[c] - 33 + c ) % 94] )
{
case 'j': d = mem[d]; break;
case 'i': c = mem[d]; break;
case '*': a = mem[d] = mem[d] / 3 + mem[d] % 3 * 19683; break;
case 'p': a = mem[d] = op( a, mem[d] ); break;
case '<':
#if '\n' != 10
if ( x == 10 ) putc( '\n', stdout ); else
#endif
putc( a, stdout );
break;
case '/':
x = getc( stdin );
#if '\n' != 10
if ( x == '\n' ) a = 10; else
#endif
if ( x == EOF ) a = 59048; else a = x;
break;
case 'v': return;
}
mem[c] = xlat2[mem[c] - 33];
if ( c == 59048 ) c = 0; else c++;
if ( d == 59048 ) d = 0; else d++;
}
}

#ifdef __GNUC__
static inline
#endif
unsigned short op( unsigned short x, unsigned short y )
{
unsigned short i = 0, j;
static const unsigned short p9[5] =
{ 1, 9, 81, 729, 6561 };
static const unsigned short o[9][9] =
{
{ 4, 3, 3, 1, 0, 0, 1, 0, 0 },
{ 4, 3, 5, 1, 0, 2, 1, 0, 2 },
{ 5, 5, 4, 2, 2, 1, 2, 2, 1 },
{ 4, 3, 3, 1, 0, 0, 7, 6, 6 },
{ 4, 3, 5, 1, 0, 2, 7, 6, 8 },
{ 5, 5, 4, 2, 2, 1, 8, 8, 7 },
{ 7, 6, 6, 7, 6, 6, 4, 3, 3 },
{ 7, 6, 8, 7, 6, 8, 4, 3, 5 },
{ 8, 8, 7, 8, 8, 7, 5, 5, 4 },
};
for ( j = 0; j < 5; j++ )
i += o[y / p9[j] % 9][x / p9[j] % 9] * p9[j];
return ( i );
}