retroforth/vm/nga-c-no-libc/retro.c

/* RETRO -------------------------------------------------------------
  A personal, minimalistic forth
  Copyright (c) 2016 - 2019 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`.

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

int getchar(void);
int putchar(int c);

int r_strlen(char *str) {
  const char *s;
  for (s = str; *s; ++s);
  return(s - str);
}

int r_strcmp(const char *s1, const char *s2) {
  while (*s1 == *s2++)
    if (*s1++ == '\0')
      return (0);
  return (*(const unsigned char *)s1 - *(const unsigned char *)(s2 - 1));
}



/*---------------------------------------------------------------------
  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         long         /* Cell size (32 bit, signed integer */
#define IMAGE_SIZE   524288 * 8   /* Amount of RAM. 4MiB by default.   */
#define ADDRESSES    1024         /* Depth of address stack            */
#define STACK_DEPTH  128          /* 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];

#include "image.c"

/*---------------------------------------------------------------------
  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(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) {
  while (*s) putchar(*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[1025];
char *string_extract(int at) {
  CELL starting = at;
  CELL i = 0;
  while(memory[starting] && i < 1024)
    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 (r_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() {
  putchar(stack_pop());
}

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;
  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");
      retro_puts("System halted.\n");
      while(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 (r_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 != 0);
}

void read_token(char *token_buffer, int echo) {
  int ch = getchar();
  if (echo != 0)
    putchar(ch);
  int 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 = getchar();
    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
  - otherwise, pass to `evaluate()` to run
  ---------------------------------------------------------------------*/

int main(int argc, char **argv) {
  char input[1024];
  IO_deviceHandlers[0] = generic_output;
  IO_queryHandlers[0] = generic_output_query;
  ngaPrepare();
  for (CELL i = 0; i < ngaImageCells; i++)
    memory[i] = ngaImage[i];
  update_rx();
  retro_puts("RETRO Listener (c) 2016-2019, Charles Childers\n\n");
  while(1) {
    Dictionary = memory[2];
    read_token(input, 0);
    evaluate(input);
  }
  return 0;
}


/* Nga ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   Copyright (c) 2008 - 2019, 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_HALT,  VM_IE,
  VM_IQ,   VM_II
};
#define NUM_OPS VM_II + 1

#ifndef NUM_DEVICES
#define NUM_DEVICES 0
#endif

CELL ngaLoadImage(char *imageFile) {
  CELL i;
  for (i = 0; i < ngaImageCells; i++)
    memory[i] = ngaImage[i];
  return i;
}

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_halt() {
  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_halt, inst_ie,
  inst_iq, inst_ii
};

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

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;
    raw = raw >> 8;
  }
  return valid;
}

void ngaProcessPackedOpcodes(CELL opcode) {
  CELL raw = opcode;
  int i;
  for (i = 0; i < 4; i++) {
    ngaProcessOpcode(raw & 0xFF);
    raw = raw >> 8;
  }
}