retroforth/interfaces/dos/repl.c

/* RETRO -------------------------------------------------------------
  A personal, minimalistic forth
  Copyright (c) 2016 - 2018 Charles Childers

  This is the `repl`, a basic interactive interface for RETRO. It is
  intended to be simple and very minimalistic, providing the minimal
  I/O and additions needed to support a basic RETRO system. For a much
  larger system, see `rre`.

  The code here is adapted to run on MS-DOS or compatible systems. I
  have built and run it using OpenWatcom and Turbo C, in small and
  tiny memory models. It's slow (as a 32-bit system running on a 16-bit
  host), but does work.

  TODO:

     This needs a virtual memory system to be useful. To fit in the
     real mode x86 memory model, I've had to limit the simulated RAM
     to around 10K cells. This is enough for the basic image to load,
     but anything using strings or the other temporary buffers will
     cause issues due to memory collisions.

  I'll include commentary throughout the source, so read on.
  ---------------------------------------------------------------------*/



/*---------------------------------------------------------------------
  Begin by including the various C headers needed.
  ---------------------------------------------------------------------*/

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


/*---------------------------------------------------------------------
  First, a few constants relating to the image format and memory
  layout. If you modify the kernel (Rx.md), these will need to be
  altered to match your memory layout.
  ---------------------------------------------------------------------*/

#define TIB            1025
#define D_OFFSET_LINK     0
#define D_OFFSET_XT       1
#define D_OFFSET_CLASS    2
#define D_OFFSET_NAME     3


/*---------------------------------------------------------------------
  Next we get into some things that relate to the Nga virtual machine
  that RETRO runs on.
  ---------------------------------------------------------------------*/

#define CELL         int          /* Cell size (32 bit, signed integer */
#define IMAGE_SIZE   12000        /* Amount of RAM. 12K cells due to   */
                                  /* memory constraints                */
#define ADDRESSES    128          /* Depth of address stack            */
#define STACK_DEPTH  32           /* Depth of data stack               */

CELL sp, rp, ip;                  /* Data, address, instruction pointers */
CELL data[STACK_DEPTH];           /* The data stack                    */
CELL address[ADDRESSES];          /* The address stack                 */
CELL memory[IMAGE_SIZE + 1];      /* The memory for the image          */

#define TOS  data[sp]             /* Shortcut for top item on stack    */
#define NOS  data[sp-1]           /* Shortcut for second item on stack */
#define TORS address[rp]          /* Shortcut for top item on address stack */

#define NUM_DEVICES  1

typedef void (*Handler)(void);

Handler IO_deviceHandlers[NUM_DEVICES + 1];
Handler IO_queryHandlers[NUM_DEVICES + 1];


/*---------------------------------------------------------------------
  Moving forward, a few variables. These are updated to point to the
  latest values in the image.
  ---------------------------------------------------------------------*/

CELL Dictionary;
CELL NotFound;
CELL interpret;


/*---------------------------------------------------------------------
  Function prototypes.
  ---------------------------------------------------------------------*/

CELL stack_pop();
void stack_push(CELL value);
int string_inject(char *str, int buffer);
char *string_extract(int at);
int d_link(CELL dt);
int d_xt(CELL dt);
int d_class(CELL dt);
int d_name(CELL dt);
int d_lookup(CELL Dictionary, char *name);
CELL d_xt_for(char *Name, CELL Dictionary);
void update_rx();
void execute(int cell);
void evaluate(char *s);
int not_eol(int ch);
void read_token(FILE *file, char *token_buffer, int echo);
CELL ngaLoadImage(char *imageFile);
void ngaPrepare();
void ngaProcessOpcode(CELL opcode);
void ngaProcessPackedOpcodes(CELL opcode);
int ngaValidatePackedOpcodes(CELL opcode);


/*---------------------------------------------------------------------
  Here's an output helper. I define a wrapper over `write` to avoid
  using `printf()`.
  ---------------------------------------------------------------------*/

void retro_puts(char *s) {
  printf("%s", s);
}


/*---------------------------------------------------------------------
  Now to the fun stuff: interfacing with the virtual machine. There are
  a things I like to have here:

  - push a value to the stack
  - pop a value off the stack
  - extract a string from the image
  - inject a string into the image.
  - lookup dictionary headers and access dictionary fields
  ---------------------------------------------------------------------*/


/*---------------------------------------------------------------------
  Stack push/pop is easy. I could avoid these, but it aids in keeping
  the code readable, so it's worth the slight overhead.
  ---------------------------------------------------------------------*/

CELL stack_pop() {
  sp--;
  return data[sp + 1];
}

void stack_push(CELL value) {
  sp++;
  data[sp] = value;
}


/*---------------------------------------------------------------------
  Strings are next. RETRO uses C-style NULL terminated strings. So I
  can easily inject or extract a string. Injection iterates over the
  string, copying it into the image. This also takes care to ensure
  that the NULL terminator is added.
  ---------------------------------------------------------------------*/

int string_inject(char *str, int buffer) {
  int i = 0;
  while (*str) {
    memory[buffer + i] = (CELL)*str++;
    memory[buffer + i + 1] = 0;
    i++;
  }
  return buffer;
}


/*---------------------------------------------------------------------
  Extracting a string is similar, but I have to iterate over the VM
  memory instead of a C string and copy the charaters into a buffer.
  This uses a static buffer (`string_data`) as I prefer to avoid using
  `malloc()`.
  ---------------------------------------------------------------------*/

char string_data[128];
char *string_extract(int at) {
  CELL starting = at;
  CELL i = 0;
  while(memory[starting] && i < 128)
    string_data[i++] = (char)memory[starting++];
  string_data[i] = 0;
  return (char *)string_data;
}


/*---------------------------------------------------------------------
  Continuing along, I now define functions to access the dictionary.

  RETRO's dictionary is a linked list. Each entry is setup like:

  0000  Link to previous entry (NULL if this is the root entry)
  0001  Pointer to definition start
  0002  Pointer to class handler
  0003  Start of a NULL terminated string with the word name

  First, functions to access each field. The offsets were defineed at
  the start of the file.
  ---------------------------------------------------------------------*/

int d_link(CELL dt) {
  return dt + D_OFFSET_LINK;
}

int d_xt(CELL dt) {
  return dt + D_OFFSET_XT;
}

int d_class(CELL dt) {
  return dt + D_OFFSET_CLASS;
}

int d_name(CELL dt) {
  return dt + D_OFFSET_NAME;
}


/*---------------------------------------------------------------------
  Next, a more complext word. This will walk through the entries to
  find one with a name that matches the specified name. This is *slow*,
  but works ok unless you have a really large dictionary. (I've not
  run into issues with this in practice).
  ---------------------------------------------------------------------*/

int d_lookup(CELL Dictionary, char *name) {
  CELL dt = 0;
  CELL i = Dictionary;
  char *dname;
  while (memory[i] != 0 && i != 0) {
    dname = string_extract(d_name(i));
    if (strcmp(dname, name) == 0) {
      dt = i;
      i = 0;
    } else {
      i = memory[i];
    }
  }
  return dt;
}


/*---------------------------------------------------------------------
  My last dictionary related word returns the `xt` pointer for a word.
  This is used to help keep various important bits up to date.
  ---------------------------------------------------------------------*/

CELL d_xt_for(char *Name, CELL Dictionary) {
  return memory[d_xt(d_lookup(Dictionary, Name))];
}



/*---------------------------------------------------------------------
  This interface tracks a few words and variables in the image. These
  are:

  Dictionary - the latest dictionary header
  NotFound   - called when a word is not found
  interpret  - the heart of the interpreter/compiler

  I have to call this periodically, as the Dictionary will change as
  new words are defined, and the user might write a new error handler
  or interpreter.
  ---------------------------------------------------------------------*/

void update_rx() {
  Dictionary = memory[2];
  NotFound = d_xt_for("err:notfound", Dictionary);
  interpret = d_xt_for("interpret", Dictionary);
}


/*---------------------------------------------------------------------
  This is an implementation of the generic output device. It's set to
  write output to the standard display.
  ---------------------------------------------------------------------*/

void generic_output() {
  printf("%c", (char)(stack_pop() & 0xFF));
}

void generic_output_query() {
  stack_push(0);
  stack_push(0);
}


/*---------------------------------------------------------------------
  With these out of the way, I implement `execute`, which takes an
  address and runs the code at it. This has a couple of interesting
  bits.

  Nga uses packed instruction bundles, with up to four instructions per
  bundle. Since RETRO requires an additional instruction to handle
  displaying a character, I define the handler for that here.

  This will also exit if the address stack depth is zero (meaning that
  the word being run, and it's dependencies) are finished.
  ---------------------------------------------------------------------*/

void execute(int cell) {
  CELL opcode;
  CELL scratch;
  rp = 1;
  ip = cell;
  while (ip < IMAGE_SIZE) {
    if (ip == NotFound) {
      retro_puts(string_extract(TIB));
      retro_puts(" ?\n");
    }
    opcode = memory[ip];
    if (ngaValidatePackedOpcodes(opcode) != 0) {
      ngaProcessPackedOpcodes(opcode);
    } else {
      retro_puts("Invalid instruction!\n");
      printf("Failed %ld\n", ip);
      exit(1);
    }
    ip++;
    if (rp == 0)
      ip = IMAGE_SIZE;
  }
}


/*---------------------------------------------------------------------
  RETRO's `interpret` word expects a token on the stack. This next
  function copies a token to the `TIB` (text input buffer) and then
  calls `interpret` to process it.
  ---------------------------------------------------------------------*/

void evaluate(char *s) {
  if (strlen(s) == 0) return;
  update_rx();
  string_inject(s, TIB);
  stack_push(TIB);
  execute(interpret);
}


/*---------------------------------------------------------------------
  `read_token` reads a token from the specified file.  It will stop on
   a whitespace or newline. It also tries to handle backspaces, though
   the success of this depends on how your terminal is configured.
  ---------------------------------------------------------------------*/

int not_eol(int ch) {
  return (ch != (char)10) && (ch != (char)13) && (ch != (char)32) && (ch != EOF) && (ch != 0);
}

void read_token(FILE *file, char *token_buffer, int echo) {
  int ch, count;
  ch = getc(file);
  if (echo != 0)
    putchar(ch);
  count = 0;
  while (not_eol(ch))
  {
    if ((ch == 8 || ch == 127) && count > 0) {
      count--;
      if (echo != 0) {
        putchar(8);
        putchar(32);
        putchar(8);
      }
    } else {
      token_buffer[count++] = ch;
    }
    ch = getc(file);
    if (echo != 0)
      putchar(ch);
  }
  token_buffer[count] = '\0';
}


/*---------------------------------------------------------------------
  The `main()` routine. This sets up the Nga VM, loads the image, and
  enters a loop.

  The loop:

  - reads input
  - if input == 'bye', exit
  - otherwise, pass to `evaluate()` to run
  ---------------------------------------------------------------------*/

int main(int argc, char **argv) {
  char input[1024];
  ngaPrepare();
  ngaLoadImage("ngaImage");
  update_rx();
  retro_puts("RETRO Listener (c) 2016-2018, Charles Childers\n\n");
  evaluate("#81");
  evaluate("!TempStringMax");
  evaluate("#6");
  evaluate("!TempStrings");
  IO_deviceHandlers[0] = generic_output;
  IO_queryHandlers[0] = generic_output_query;
  while(1) {
    Dictionary = memory[2];
    read_token(stdin, input, 0);
    if (strcmp(input, "bye") == 0)
      exit(0);
    else
      evaluate(input);
  }
}


/* Nga ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   Copyright (c) 2008 - 2018, Charles Childers
   Copyright (c) 2009 - 2010, Luke Parrish
   Copyright (c) 2010,        Marc Simpson
   Copyright (c) 2010,        Jay Skeer
   Copyright (c) 2011,        Kenneth Keating
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */

enum vm_opcode {
  VM_NOP,  VM_LIT,    VM_DUP,   VM_DROP,    VM_SWAP,   VM_PUSH,  VM_POP,
  VM_JUMP, VM_CALL,   VM_CCALL, VM_RETURN,  VM_EQ,     VM_NEQ,   VM_LT,
  VM_GT,   VM_FETCH,  VM_STORE, VM_ADD,     VM_SUB,    VM_MUL,   VM_DIVMOD,
  VM_AND,  VM_OR,     VM_XOR,   VM_SHIFT,   VM_ZRET,   VM_END,   VM_IE,
  VM_IQ,   VM_II
};
#define NUM_OPS VM_II + 1

#ifndef NUM_DEVICES
#define NUM_DEVICES 0
#endif

CELL ngaLoadImage(char *imageFile) {
  FILE *fp;
  CELL imageSize;
  long fileLen;
  CELL i;
  if ((fp = fopen(imageFile, "rb")) != NULL) {
    /* Determine length (in cells) */
    fseek(fp, 0, SEEK_END);
    fileLen = ftell(fp) / sizeof(CELL);
    rewind(fp);
    /* Read the file into memory */
    imageSize = fread(&memory, sizeof(CELL), fileLen, fp);
    fclose(fp);
  } else {
    retro_puts("Unable to find the ngaImage!\n");
    printf("%ld", ip);
    exit(1);
  }
  return imageSize;
}

void ngaPrepare() {
  ip = sp = rp = 0;
  for (ip = 0; ip < IMAGE_SIZE; ip++)
    memory[ip] = VM_NOP;
  for (ip = 0; ip < STACK_DEPTH; ip++)
    data[ip] = 0;
  for (ip = 0; ip < ADDRESSES; ip++)
    address[ip] = 0;
}

void inst_nop() {
}

void inst_lit() {
  sp++;
  ip++;
  TOS = memory[ip];
}

void inst_dup() {
  sp++;
  data[sp] = NOS;
}

void inst_drop() {
  data[sp] = 0;
   if (--sp < 0)
     ip = IMAGE_SIZE;
}

void inst_swap() {
  CELL a;
  a = TOS;
  TOS = NOS;
  NOS = a;
}

void inst_push() {
  rp++;
  TORS = TOS;
  inst_drop();
}

void inst_pop() {
  sp++;
  TOS = TORS;
  rp--;
}

void inst_jump() {
  ip = TOS - 1;
  inst_drop();
}

void inst_call() {
  rp++;
  TORS = ip;
  ip = TOS - 1;
  inst_drop();
}

void inst_ccall() {
  CELL a, b;
  a = TOS; inst_drop();  /* False */
  b = TOS; inst_drop();  /* Flag  */
  if (b != 0) {
    rp++;
    TORS = ip;
    ip = a - 1;
  }
}

void inst_return() {
  ip = TORS;
  rp--;
}

void inst_eq() {
  NOS = (NOS == TOS) ? -1 : 0;
  inst_drop();
}

void inst_neq() {
  NOS = (NOS != TOS) ? -1 : 0;
  inst_drop();
}

void inst_lt() {
  NOS = (NOS < TOS) ? -1 : 0;
  inst_drop();
}

void inst_gt() {
  NOS = (NOS > TOS) ? -1 : 0;
  inst_drop();
}

void inst_fetch() {
  switch (TOS) {
    case -1: TOS = sp - 1; break;
    case -2: TOS = rp; break;
    case -3: TOS = IMAGE_SIZE; break;
    default: TOS = memory[TOS]; break;
  }
}

void inst_store() {
  if (TOS <= IMAGE_SIZE && TOS >= 0) {
    memory[TOS] = NOS;
    inst_drop();
    inst_drop();
  } else {
    ip = IMAGE_SIZE;
  }
}

void inst_add() {
  NOS += TOS;
  inst_drop();
}

void inst_sub() {
  NOS -= TOS;
  inst_drop();
}

void inst_mul() {
  NOS *= TOS;
  inst_drop();
}

void inst_divmod() {
  CELL a, b;
  a = TOS;
  b = NOS;
  TOS = b / a;
  NOS = b % a;
}

void inst_and() {
  NOS = TOS & NOS;
  inst_drop();
}

void inst_or() {
  NOS = TOS | NOS;
  inst_drop();
}

void inst_xor() {
  NOS = TOS ^ NOS;
  inst_drop();
}

void inst_shift() {
  CELL y = TOS;
  CELL x = NOS;
  if (TOS < 0)
    NOS = NOS << (TOS * -1);
  else {
    if (x < 0 && y > 0)
      NOS = x >> y | ~(~0U >> y);
    else
      NOS = x >> y;
  }
  inst_drop();
}

void inst_zret() {
  if (TOS == 0) {
    inst_drop();
    ip = TORS;
    rp--;
  }
}

void inst_end() {
  ip = IMAGE_SIZE;
}

void inst_ie() {
  sp++;
  TOS = NUM_DEVICES;
}

void inst_iq() {
  CELL Device = TOS;
  inst_drop();
  IO_queryHandlers[Device]();
}

void inst_ii() {
  CELL Device = TOS;
  inst_drop();
  IO_deviceHandlers[Device]();
}

Handler instructions[NUM_OPS] = {
  inst_nop, inst_lit, inst_dup, inst_drop, inst_swap, inst_push, inst_pop,
  inst_jump, inst_call, inst_ccall, inst_return, inst_eq, inst_neq, inst_lt,
  inst_gt, inst_fetch, inst_store, inst_add, inst_sub, inst_mul, inst_divmod,
  inst_and, inst_or, inst_xor, inst_shift, inst_zret, inst_end, inst_ie,
  inst_iq, inst_ii
};

void ngaProcessOpcode(CELL opcode) {
  if (opcode != 0)
    instructions[opcode]();
}

CELL o1, o2, o3, o4;

int ngaValidatePackedOpcodes(CELL opcode) {
  CELL raw = opcode;
  CELL current;
  int valid = -1;
  int i;
  for (i = 0; i < 4; i++) {
    current = raw & 0xFF;
    if (!(current >= 0 && current <= 29))
      valid = 0;
    if (i == 0)
      o1 = current;
    if (i == 1)
      o2 = current;
    if (i == 2)
      o3 = current;
    if (i == 3)
      o4 = current;
    raw = raw >> 8;
  }
  return valid;
}

void ngaProcessPackedOpcodes(CELL opcode) {
  ngaProcessOpcode(o1);
  ngaProcessOpcode(o2);
  ngaProcessOpcode(o3);
  ngaProcessOpcode(o4);
}