Write a brainfuck compiler

Python, 1974 chars

import sys
s='\x11\x75\x30\xbc\x08\x4b\x03\x3c'
k=[]
for c in sys.stdin.read():
 if'>'==c:s+='\x84\x01\x01'
 if'<'==c:s+='\x84\x01\xff'
 if'+'==c:s+='\x2a\x1b\x5c\x33\x04\x60\x91\x54'
 if'-'==c:s+='\x2a\x1b\x5c\x33\x04\x64\x91\x54'
 if'['==c:k+=[len(s)];s+='\x2a\x1b\x33\x99\x00\x00'
 if']'==c:a=k[-1];k=k[:-1];d=len(s)-a;s=s[:a+4]+'%c%c'%(d>>8,d&255)+s[a+6:]+'\xa7%c%c'%(-d>>8&255,-d&255)
 if','==c:s+='\x2a\x1b\xb2\x00\x02\xb6\x00\x03\x91\x54'
 if'.'==c:s+='\xb2\x00\x04\x59\x2a\x1b\x33\xb6\x00\x05\xb6\x00\x06'
s+='\xb1'
n=len(s)
sys.stdout.write('\xca\xfe\xba\xbe\x00\x03\x00-\x00+\n\x00\x08\x00\x13\t\x00\x14\x00\x15\n\x00\x16\x00\x17\t\x00\x14\x00\x18\n\x00\x19\x00\x1a\n\x00\x19\x00\x1b\x07\x00\x1c\x07\x00\x1d\x01\x00\x06<init>\x01\x00\x03()V\x01\x00\x04Code\x01\x00\x0fLineNumberTable\x01\x00\x04main\x01\x00\x16([Ljava/lang/String;)V\x01\x00\nExceptions\x07\x00\x1e\x01\x00\nSourceFile\x01\x00\x06B.java\x0c\x00\t\x00\n\x07\x00\x1f\x0c\x00 \x00!\x07\x00"\x0c\x00#\x00$\x0c\x00%\x00&\x07\x00\'\x0c\x00(\x00)\x0c\x00*\x00\n\x01\x00\x01B\x01\x00\x10java/lang/Object\x01\x00\x13java/io/IOException\x01\x00\x10java/lang/System\x01\x00\x02in\x01\x00\x15Ljava/io/InputStream;\x01\x00\x13java/io/InputStream\x01\x00\x04read\x01\x00\x03()I\x01\x00\x03out\x01\x00\x15Ljava/io/PrintStream;\x01\x00\x13java/io/PrintStream\x01\x00\x05write\x01\x00\x04(I)V\x01\x00\x05flush\x00!\x00\x07\x00\x08\x00\x00\x00\x00\x00\x02\x00\x01\x00\t\x00\n\x00\x01\x00\x0b\x00\x00\x00\x1d\x00\x01\x00\x01\x00\x00\x00\x05*\xb7\x00\x01\xb1\x00\x00\x00\x01\x00\x0c\x00\x00\x00\x06\x00\x01\x00\x00\x00\x03\x00\t\x00\r\x00\x0e\x00\x02\x00\x0b\x00\x00'+'%c%c'%((n+60)>>8,(n+60)&255)+'\x00\x04\x00\x03\x00\x00'+'%c%c'%(n>>8,n&255)+s+'\x00\x00\x00\x01\x00\x0c\x00\x00\x00*\x00\n\x00\x00\x00\x05\x00\x06\x00\x06\x00\x08\x00\t\x00\x0b\x00\x0b\x00\x13\x00\r\x00\x1d\x00\x0f\x00&\x00\x11\x00,\x00\x12\x002\x00\x14\x008\x00\x15\x00\x0f\x00\x00\x00\x04\x00\x01\x00\x10\x00\x01\x00\x11\x00\x00\x00\x02\x00\x12')

Below are the translations to java bytecode. local 0 is a byte array representing the tape, local 1 is the data pointer.

>  iinc 1,+1
<  iinc 1,-1
+  aload_0;iload_1;dup2;baload;iconst_1;iadd;i2b;bastore
-  aload_0;iload_1;dup2;baload;iconst_1;isub;i2b;bastore
[  aload_0;iload_1;baload;ifeq xx xx
]  goto xx xx
,  aload_0;iload_1;getstatic #2;invokevirtual #3;i2b;bastore
.  getstatic #4;dup;aload_0;iload_1;baload;invokevirtual #5;invokevirtual #6

The xx xx are offsets to reach the matching bracket. #2 is System.in, #3 is read(), #4 is System.out, #5 is write(), and #6 is flush().

The preamble allocates a 30000 byte array and initializes the tape position to 0.

The giant wrapper at the end was generated by compiling a dummy B.java file with code for one of each opcode (to induce generation of the correct constant tables and other junk), then performing delicate surgery on it.

Run it like

python bfc.py < input.b > B.class
java B

Disassemble with

javap -c B

I'm sure it could be golfed some more. I'm just happy it works...


C, 866 783 bytes

Since my code outputs 32 bit ELF executable I can't promise that it will work on everyones setup. It took enough tweaking to get the executable to stop segfaulting on my computer.

For anyone trying to run this:

$ uname --all
Linux 4.4.0-24-generic #43-Ubuntu SMP Wed Jun 8 19:27:37 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

A Brainfuck program is read from stdin and the compiled ELF is written to stdout.

#define P *(t++)
#define C case
#define B break
char a[30000],b[65535],f,*t=b;*c[100];**d=c;main(g){P=188;t+=4;while((f=getchar())!=-1)switch(f){C'>':P=68;B;C'<':P=76;B;C'+':P=254;P=4;P=36;B;C'-':P=254;P=12;P=36;B;C'.':P=187;t+=4;P=137;P=225;P=186;P=1;t+=3;P=184;P=4;t+=3;P=205;P=128;B;C',':P=187;P=1;t+=3;P=137;P=225;P=186;P=1;t+=3;P=184;P=3;t+=3;P=205;P=128;B;C'[':P=138;P=4;P=36;P=133;P=192;P=15;P=132;t+=4;*d=(int*)t-1;d++;B;C']':P=138;P=4;P=36;P=133;P=192;P=15;P=133;t+=4;d--;g=((char*)(*d+1))-t;*((int*)t-1)=g;**d=-g;B;}P=184;P=1;t+=3;P=187;t+=4;P=205;P=128;*(int*)(b+1)=0x8048054+t-b;long long z[]={282579962709375,0,4295163906,223472812116,0,4297064500,4294967296,577727389698621440,36412867248128,30064779550,140720308490240};write(1,&z,84);write(1,b,t-b);write(1,a,30000);}

Ungolfed

In the ungolfed version of the code, you can get a better idea of what's going on. The character array at the end of the golfed code is an encoding of the ELF and program header in the ungolfed code. This code also show how each Brainfuck instruction is translated into bytecode.

#include <linux/elf.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <stdint.h>

#define MAX_BIN_LEN 65535
#define MAX_JUMPS 100

unsigned int org = 0x08048000;



unsigned char move_right[] = {0x44};                              /*inc   esp         */

unsigned char move_left[]  = {0x4c};                              /*dec   esp         */

unsigned char inc_cell[]   = {0xfe,0x04,0x24};                    /*inc   [esp]       */

unsigned char dec_cell[]   = {0xfe,0x0c,0x24};                    /*dec   [esp]       */

unsigned char read_char[]  = {0xbb,0x00,0x00,0x00,0x00,           /*mov   ebx,  0     */
                              0x89,0xe1,                          /*mov   ecx,  esp   */
                              0xba,0x01,0x00,0x00,0x00,           /*mov   edx,  1     */
                              0xb8,0x03,0x00,0x00,0x00,           /*mov   eax,  3     */
                              0xcd,0x80};                         /*int   0x80        */

unsigned char print_char[] = {0xbb,0x01,0x00,0x00,0x00,           /*mov   ebx,  1     */
                              0x89,0xe1,                          /*mov   ecx,  esp   */
                              0xba,0x01,0x00,0x00,0x00,           /*mov   edx,  1     */
                              0xb8,0x04,0x00,0x00,0x00,           /*mov   eax,  4     */
                              0xcd,0x80};                         /*int   0x80        */


unsigned char loop_start[] = {0x8a,0x04,0x24,                     /*mov   eax,  [esp] */
                              0x85,0xc0,                          /*test  eax,  eax   */
                              0x0f,0x84,0x00,0x00,0x00,0x00};     /*je    int32_t     */

unsigned char loop_end[]   = {0x8a,0x04,0x24,                     /*mov   eax,  [esp] */
                              0x85,0xc0,                          /*test  eax,  eax   */
                              0x0f,0x85,0x00,0x00,0x00,0x00};     /*jne   int32_t     */

unsigned char call_exit[]  = {0xb8,0x01,0x00,0x00,0x00,           /*mov   eax,  1     */
                              0xbb,0x00,0x00,0x00,0x00,           /*mov   ebx,  0     */
                              0xcd,0x80};                         /*int   0x80        */
unsigned char prelude[]    = {0xbc,0x00,0x00,0x00,0x00};          /*mov   esp, int32_t*/

unsigned char tape[100];

int main(){
    unsigned char text[MAX_BIN_LEN];
    unsigned char *txt_ptr = text;

    int32_t *loop_jmps[MAX_JUMPS];
    int32_t **loop_jmps_ptr = loop_jmps;

    Elf32_Off entry;

    entry = org + sizeof(Elf32_Ehdr) + 1 * sizeof(Elf32_Phdr);

    memcpy(txt_ptr,prelude,sizeof(prelude));
    txt_ptr += sizeof(prelude);
    char input;
    while((input = getchar()) != -1){
        switch(input){
            case '>':
                memcpy(txt_ptr,move_right,sizeof(move_right));
                txt_ptr += sizeof(move_right);
                break;
            case '<':
                memcpy(txt_ptr,move_left,sizeof(move_left));
                txt_ptr += sizeof(move_left);
                break;
            case '+':
                memcpy(txt_ptr,inc_cell,sizeof(inc_cell));
                txt_ptr += sizeof(inc_cell);
                break;
            case '-':
                memcpy(txt_ptr,dec_cell,sizeof(dec_cell));
                txt_ptr += sizeof(dec_cell);
                break;
            case '.':
                memcpy(txt_ptr,print_char,sizeof(print_char));
                txt_ptr += sizeof(print_char);
                break;
            case ',':
                memcpy(txt_ptr,read_char,sizeof(read_char));
                txt_ptr += sizeof(read_char);
                break;
            case '[':
                memcpy(txt_ptr,loop_start,sizeof(loop_start));
                txt_ptr += sizeof(loop_start);
                *loop_jmps_ptr = (int32_t*) txt_ptr - 1;
                loop_jmps_ptr++;
                break;
            case ']':
                memcpy(txt_ptr,loop_end,sizeof(loop_end));
                txt_ptr += sizeof(loop_end);
                loop_jmps_ptr--;
                int32_t offset = ((unsigned char*) (*loop_jmps_ptr + 1)) - txt_ptr;
                *((int32_t*)txt_ptr - 1) = offset;
                **loop_jmps_ptr = -offset;
                break;
        }
    }

    memcpy(txt_ptr,call_exit,sizeof(call_exit));
    txt_ptr += sizeof(call_exit);

    *(int32_t*)(text + 1) = entry + (txt_ptr - text);


    Elf32_Ehdr ehdr = {
        {0x7F,'E','L','F',ELFCLASS32,ELFDATA2LSB,EV_CURRENT,0,0,0,0,0,0,0,0,0},
        ET_EXEC,
        EM_386,
        EV_CURRENT,
        entry,
        sizeof(Elf32_Ehdr),
        0,
        0,
        sizeof(Elf32_Ehdr),
        sizeof(Elf32_Phdr),
        1,
        0,
        0,
        SHN_UNDEF,
    };

    Elf32_Phdr phdr = {
        PT_LOAD,
        0,
        org,
        org,
        sizeof(Elf32_Ehdr) + sizeof(Elf32_Phdr) + (txt_ptr - text),
        sizeof(Elf32_Ehdr) + sizeof(Elf32_Phdr) + (txt_ptr - text),
        PF_R | PF_X | PF_W,
        0x1000,
    };

    int out = open("a.out",O_CREAT|O_TRUNC|O_WRONLY,S_IRWXU);
    write(out,&ehdr,sizeof(Elf32_Ehdr));
    write(out,&phdr,sizeof(Elf32_Phdr));

    write(out,text,txt_ptr-text);
    write(out,tape,sizeof(tape));
    close(out);
}

Self Modifying BrainFuck

In order to save on bytes, the tape for my compiler isn't allocated in a .bss section or anything fancy like that. Instead, the tape is 30,000 null bytes written directly after the compiled byte code of the Brainfuck program. Knowing this, and being aware of what byte code is generated by my compiler means that you can generate or modify byte code at runtime. A simple illustration of this 'feature' is a Brainfuck program that sets its own exit value.

 <<<<<<+ 

The program goes off the left edge of the tape into the byte code to the point that the exit code is normally set 0. Incrementing this byte causes the exit code to be set to 1 instead of 0 when the program eventually exits. With persistence, this could be used to do system level programming in Brainfuck.


16-bit x86 assembly code, 104 bytes

This code is from 2014, but I just found the task.

;compliant version, non-commands are ignored, but 104 bytes long

[bits 16]  
[org 0x100]  
; assume bp=091e used  
; assume di=fffe  
; assume si=0100  
; assume dx=cs (see here)  
; assume cx=00ff  
; assume bx=0000  
; assume ax=0000 used (ah)  
; assume sp=fffe  
start:
        mov al, code_nothing - start  
code_start:
        mov ch, 0x7f ; allow bigger programs  
        mov bx, cx  
        mov di, cx  
        rep stosb  
        mov bp, find_right + start - code_start ;cache loop head for smaller compiled programs  
        jmp code_start_end  
find_right:
        pop si  
        dec si  
        dec si ;point to loop head  
        cmp [bx], cl  
        jne loop_right_end  
loop_right:
        lodsb  
        cmp al, 0xD5 ; the "bp" part of "call bp" (because 0xFF is not unique, watch for additional '[')  
        jne loop_left  
        inc cx  
loop_left:
        cmp al, 0xC3 ; ret (watch for ']')  
        jne loop_right  
        loop loop_right ;all brackets matched when cx==0  
        db 0x3c ;cmp al, xx (mask push)  
loop_right_end:
        push si  
        lodsw ; skip "call" or dummy "dec" instruction, depending on context  
        push si  
code_sqright:
        ret  
code_dec:
        dec byte [bx]  
code_start_end:
        db '$' ;end DOS string, also "and al, xx"  
code_inc:
        inc byte [bx]  
        db '$'  
code_right:
        inc bx ;al -> 2  
code_nothing:
        db '$'  
code_left:
        dec bx  
        db '$'  
code_sqleft:
        call bp  
        db '$'  
; create lookup table  
real_start:
        inc byte [bx+'<'] ;point to code_left  
        dec byte [bx+'>'] ;point to code_right  
        mov byte [bx+'['], code_sqleft - start  
        mov byte [bx+']'], code_sqright - start  
        lea sp, [bx+45+2] ;'+' + 4 (2b='+', 2c=',', 2d='-', 2e='.')  
        push (code_dec - start) + (code_dot - start) * 256  
        push (code_inc - start) + (code_comma - start) * 256  
pre_write:
        mov ah, code_start >> 8  
        xchg dx, ax  
; write  
        mov ah, 9  
        int 0x21  
; read  
code_comma:
        mov dl, 0xff  
        db 0x3d ; cmp ax, xxxx (mask mov)  
code_dot:
        mov dl, [bx]  
        mov ah, 6  
        int 0x21  
        mov [bx], al  
        db '$'  
        db 0xff ; parameter for '$', doubles as test for zero  
; switch  
        xlatb  
        jne pre_write  
  ; next two lines can also be removed  
  ; if the program ends with extra ']'  
  ; and then we are at 100 bytes... :-)  
the_end:
        mov dl, 0xC3  
        int 0x21  
        int 0x20