652 lines
16 KiB
C
652 lines
16 KiB
C
/* RETRO -------------------------------------------------------------
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A personal, minimalistic forth
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Copyright (c) 2016 - 2018 Charles Childers
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This is the `repl`, a basic interactive interface for RETRO. It is
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intended to be simple and very minimalistic, providing the minimal
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I/O and additions needed to support a basic RETRO system. For a much
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larger system, see `rre`.
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The code here is adapted to run on MS-DOS or compatible systems. I
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have built and run it using OpenWatcom and Turbo C, in small and
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tiny memory models. It's slow (as a 32-bit system running on a 16-bit
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host), but does work.
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TODO:
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This needs a virtual memory system to be useful. To fit in the
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real mode x86 memory model, I've had to limit the simulated RAM
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to around 10K cells. This is enough for the basic image to load,
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but anything using strings or the other temporary buffers will
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cause issues due to memory collisions.
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I'll include commentary throughout the source, so read on.
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---------------------------------------------------------------------*/
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/*---------------------------------------------------------------------
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Begin by including the various C headers needed.
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---------------------------------------------------------------------*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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/*---------------------------------------------------------------------
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First, a few constants relating to the image format and memory
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layout. If you modify the kernel (Rx.md), these will need to be
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altered to match your memory layout.
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---------------------------------------------------------------------*/
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#define TIB 1025
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#define D_OFFSET_LINK 0
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#define D_OFFSET_XT 1
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#define D_OFFSET_CLASS 2
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#define D_OFFSET_NAME 3
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/*---------------------------------------------------------------------
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Next we get into some things that relate to the Nga virtual machine
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that RETRO runs on.
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---------------------------------------------------------------------*/
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#define CELL long int /* Cell size (32 bit, signed integer */
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#define IMAGE_SIZE 10000 /* Amount of RAM. 10K cells due to */
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/* memory constraints */
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#define ADDRESSES 128 /* Depth of address stack */
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#define STACK_DEPTH 32 /* Depth of data stack */
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CELL sp, rp, ip; /* Data, address, instruction pointers */
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CELL data[STACK_DEPTH]; /* The data stack */
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CELL address[ADDRESSES]; /* The address stack */
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CELL memory[IMAGE_SIZE + 1]; /* The memory for the image */
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#define TOS data[sp] /* Shortcut for top item on stack */
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#define NOS data[sp-1] /* Shortcut for second item on stack */
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#define TORS address[rp] /* Shortcut for top item on address stack */
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/*---------------------------------------------------------------------
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Moving forward, a few variables. These are updated to point to the
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latest values in the image.
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---------------------------------------------------------------------*/
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CELL Dictionary;
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CELL NotFound;
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CELL interpret;
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/*---------------------------------------------------------------------
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Function prototypes.
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---------------------------------------------------------------------*/
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CELL stack_pop();
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void stack_push(CELL value);
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int string_inject(char *str, int buffer);
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char *string_extract(int at);
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int d_link(CELL dt);
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int d_xt(CELL dt);
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int d_class(CELL dt);
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int d_name(CELL dt);
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int d_lookup(CELL Dictionary, char *name);
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CELL d_xt_for(char *Name, CELL Dictionary);
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void update_rx();
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void execute(int cell);
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void evaluate(char *s);
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int not_eol(int ch);
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void read_token(FILE *file, char *token_buffer, int echo);
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CELL ngaLoadImage(char *imageFile);
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void ngaPrepare();
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void ngaProcessOpcode(CELL opcode);
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void ngaProcessPackedOpcodes(int opcode);
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int ngaValidatePackedOpcodes(CELL opcode);
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/*---------------------------------------------------------------------
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Here's an output helper. I define a wrapper over `write` to avoid
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using `printf()`.
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---------------------------------------------------------------------*/
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void retro_puts(char *s) {
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printf(s);
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}
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/*---------------------------------------------------------------------
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Now to the fun stuff: interfacing with the virtual machine. There are
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a things I like to have here:
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- push a value to the stack
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- pop a value off the stack
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- extract a string from the image
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- inject a string into the image.
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- lookup dictionary headers and access dictionary fields
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---------------------------------------------------------------------*/
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/*---------------------------------------------------------------------
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Stack push/pop is easy. I could avoid these, but it aids in keeping
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the code readable, so it's worth the slight overhead.
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---------------------------------------------------------------------*/
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CELL stack_pop() {
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sp--;
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return data[sp + 1];
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}
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void stack_push(CELL value) {
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sp++;
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data[sp] = value;
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}
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/*---------------------------------------------------------------------
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Strings are next. RETRO uses C-style NULL terminated strings. So I
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can easily inject or extract a string. Injection iterates over the
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string, copying it into the image. This also takes care to ensure
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that the NULL terminator is added.
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---------------------------------------------------------------------*/
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int string_inject(char *str, int buffer) {
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int i = 0;
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while (*str) {
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memory[buffer + i] = (CELL)*str++;
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memory[buffer + i + 1] = 0;
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i++;
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}
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return buffer;
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}
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/*---------------------------------------------------------------------
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Extracting a string is similar, but I have to iterate over the VM
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memory instead of a C string and copy the charaters into a buffer.
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This uses a static buffer (`string_data`) as I prefer to avoid using
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`malloc()`.
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---------------------------------------------------------------------*/
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char string_data[128];
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char *string_extract(int at) {
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CELL starting = at;
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CELL i = 0;
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while(memory[starting] && i < 128)
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string_data[i++] = (char)memory[starting++];
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string_data[i] = 0;
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return (char *)string_data;
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}
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/*---------------------------------------------------------------------
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Continuing along, I now define functions to access the dictionary.
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RETRO's dictionary is a linked list. Each entry is setup like:
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0000 Link to previous entry (NULL if this is the root entry)
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0001 Pointer to definition start
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0002 Pointer to class handler
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0003 Start of a NULL terminated string with the word name
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First, functions to access each field. The offsets were defineed at
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the start of the file.
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---------------------------------------------------------------------*/
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int d_link(CELL dt) {
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return dt + D_OFFSET_LINK;
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}
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int d_xt(CELL dt) {
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return dt + D_OFFSET_XT;
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}
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int d_class(CELL dt) {
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return dt + D_OFFSET_CLASS;
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}
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int d_name(CELL dt) {
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return dt + D_OFFSET_NAME;
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}
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/*---------------------------------------------------------------------
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Next, a more complext word. This will walk through the entries to
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find one with a name that matches the specified name. This is *slow*,
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but works ok unless you have a really large dictionary. (I've not
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run into issues with this in practice).
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---------------------------------------------------------------------*/
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int d_lookup(CELL Dictionary, char *name) {
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CELL dt = 0;
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CELL i = Dictionary;
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char *dname;
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while (memory[i] != 0 && i != 0) {
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dname = string_extract(d_name(i));
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if (strcmp(dname, name) == 0) {
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dt = i;
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i = 0;
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} else {
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i = memory[i];
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}
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}
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return dt;
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}
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/*---------------------------------------------------------------------
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My last dictionary related word returns the `xt` pointer for a word.
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This is used to help keep various important bits up to date.
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---------------------------------------------------------------------*/
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CELL d_xt_for(char *Name, CELL Dictionary) {
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return memory[d_xt(d_lookup(Dictionary, Name))];
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}
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/*---------------------------------------------------------------------
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This interface tracks a few words and variables in the image. These
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are:
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Dictionary - the latest dictionary header
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NotFound - called when a word is not found
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interpret - the heart of the interpreter/compiler
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I have to call this periodically, as the Dictionary will change as
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new words are defined, and the user might write a new error handler
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or interpreter.
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---------------------------------------------------------------------*/
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void update_rx() {
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Dictionary = memory[2];
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NotFound = d_xt_for("err:notfound", Dictionary);
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interpret = d_xt_for("interpret", Dictionary);
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}
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/*---------------------------------------------------------------------
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With these out of the way, I implement `execute`, which takes an
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address and runs the code at it. This has a couple of interesting
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bits.
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Nga uses packed instruction bundles, with up to four instructions per
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bundle. Since RETRO requires an additional instruction to handle
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displaying a character, I define the handler for that here.
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This will also exit if the address stack depth is zero (meaning that
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the word being run, and it's dependencies) are finished.
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---------------------------------------------------------------------*/
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#define IO_TTY_PUTC 1000
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void execute(int cell) {
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CELL opcode;
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CELL scratch;
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rp = 1;
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ip = cell;
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while (ip < IMAGE_SIZE) {
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if (ip == NotFound) {
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retro_puts(string_extract(TIB));
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retro_puts(" ?\n");
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}
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opcode = memory[ip];
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if (ngaValidatePackedOpcodes(opcode) != 0) {
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ngaProcessPackedOpcodes(opcode);
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} else {
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switch (opcode) {
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case IO_TTY_PUTC:
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printf("%c", (char)(stack_pop() & 0xFF));
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break;
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default:
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retro_puts("Invalid instruction!\n");
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printf("Failed %ld\n", ip);
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exit(1);
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}
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}
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ip++;
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if (rp == 0)
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ip = IMAGE_SIZE;
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}
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}
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/*---------------------------------------------------------------------
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RETRO's `interpret` word expects a token on the stack. This next
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function copies a token to the `TIB` (text input buffer) and then
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calls `interpret` to process it.
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---------------------------------------------------------------------*/
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void evaluate(char *s) {
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if (strlen(s) == 0) return;
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update_rx();
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string_inject(s, TIB);
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stack_push(TIB);
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execute(interpret);
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}
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/*---------------------------------------------------------------------
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`read_token` reads a token from the specified file. It will stop on
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a whitespace or newline. It also tries to handle backspaces, though
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the success of this depends on how your terminal is configured.
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---------------------------------------------------------------------*/
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int not_eol(int ch) {
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return (ch != (char)10) && (ch != (char)13) && (ch != (char)32) && (ch != EOF) && (ch != 0);
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}
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void read_token(FILE *file, char *token_buffer, int echo) {
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int ch, count;
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ch = getc(file);
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if (echo != 0)
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putchar(ch);
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count = 0;
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while (not_eol(ch))
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{
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if ((ch == 8 || ch == 127) && count > 0) {
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count--;
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if (echo != 0) {
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putchar(8);
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putchar(32);
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putchar(8);
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}
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} else {
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token_buffer[count++] = ch;
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}
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ch = getc(file);
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if (echo != 0)
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putchar(ch);
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}
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token_buffer[count] = '\0';
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}
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/*---------------------------------------------------------------------
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The `main()` routine. This sets up the Nga VM, loads the image, and
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enters a loop.
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The loop:
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- reads input
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- if input == 'bye', exit
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- otherwise, pass to `evaluate()` to run
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---------------------------------------------------------------------*/
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int main(int argc, char **argv) {
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char input[1024];
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ngaPrepare();
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ngaLoadImage("ngaImage");
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update_rx();
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retro_puts("RETRO Listener (c) 2016-2018, Charles Childers\n\n");
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while(1) {
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Dictionary = memory[2];
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read_token(stdin, input, 0);
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if (strcmp(input, "bye") == 0)
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exit(0);
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else
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evaluate(input);
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}
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}
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/* Nga ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Copyright (c) 2008 - 2017, Charles Childers
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Copyright (c) 2009 - 2010, Luke Parrish
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Copyright (c) 2010, Marc Simpson
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Copyright (c) 2010, Jay Skeer
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Copyright (c) 2011, Kenneth Keating
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
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enum vm_opcode {
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VM_NOP, VM_LIT, VM_DUP, VM_DROP, VM_SWAP, VM_PUSH, VM_POP,
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VM_JUMP, VM_CALL, VM_CCALL, VM_RETURN, VM_EQ, VM_NEQ, VM_LT,
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VM_GT, VM_FETCH, VM_STORE, VM_ADD, VM_SUB, VM_MUL, VM_DIVMOD,
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VM_AND, VM_OR, VM_XOR, VM_SHIFT, VM_ZRET, VM_END
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};
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#define NUM_OPS VM_END + 1
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CELL ngaLoadImage(char *imageFile) {
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FILE *fp;
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CELL imageSize;
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long fileLen;
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if ((fp = fopen(imageFile, "rb")) != NULL) {
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/* Determine length (in cells) */
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fseek(fp, 0, SEEK_END);
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fileLen = ftell(fp) / sizeof(CELL);
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rewind(fp);
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/* Read the file into memory */
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imageSize = fread(&memory, sizeof(CELL), fileLen, fp);
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fclose(fp);
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}
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else {
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retro_puts("Unable to find the ngaImage!\n");
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printf("%ld", ip);
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exit(1);
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}
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return imageSize;
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}
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void ngaPrepare() {
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ip = sp = rp = 0;
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for (ip = 0; ip < IMAGE_SIZE; ip++)
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memory[ip] = VM_NOP;
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for (ip = 0; ip < STACK_DEPTH; ip++)
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data[ip] = 0;
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for (ip = 0; ip < ADDRESSES; ip++)
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address[ip] = 0;
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}
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void inst_nop() {
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}
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void inst_lit() {
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sp++;
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ip++;
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TOS = memory[ip];
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}
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void inst_dup() {
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sp++;
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data[sp] = NOS;
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}
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void inst_drop() {
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data[sp] = 0;
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if (--sp < 0)
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ip = IMAGE_SIZE;
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}
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void inst_swap() {
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int a;
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a = TOS;
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TOS = NOS;
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NOS = a;
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}
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void inst_push() {
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rp++;
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TORS = TOS;
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inst_drop();
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}
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void inst_pop() {
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sp++;
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TOS = TORS;
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rp--;
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}
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void inst_jump() {
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ip = TOS - 1;
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inst_drop();
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}
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void inst_call() {
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rp++;
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TORS = ip;
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ip = TOS - 1;
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inst_drop();
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}
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void inst_ccall() {
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int a, b;
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a = TOS; inst_drop(); /* False */
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b = TOS; inst_drop(); /* Flag */
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if (b != 0) {
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rp++;
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TORS = ip;
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ip = a - 1;
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}
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}
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void inst_return() {
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ip = TORS;
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rp--;
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}
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void inst_eq() {
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NOS = (NOS == TOS) ? -1 : 0;
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inst_drop();
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}
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void inst_neq() {
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NOS = (NOS != TOS) ? -1 : 0;
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inst_drop();
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}
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void inst_lt() {
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NOS = (NOS < TOS) ? -1 : 0;
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inst_drop();
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}
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void inst_gt() {
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NOS = (NOS > TOS) ? -1 : 0;
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inst_drop();
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}
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void inst_fetch() {
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switch (TOS) {
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case -1: TOS = sp - 1; break;
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case -2: TOS = rp; break;
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case -3: TOS = IMAGE_SIZE; break;
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default: TOS = memory[TOS]; break;
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}
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}
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void inst_store() {
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if (TOS <= IMAGE_SIZE && TOS >= 0) {
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memory[TOS] = NOS;
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inst_drop();
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inst_drop();
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} else {
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ip = IMAGE_SIZE;
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}
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}
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void inst_add() {
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NOS += TOS;
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inst_drop();
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}
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void inst_sub() {
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NOS -= TOS;
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inst_drop();
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}
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void inst_mul() {
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NOS *= TOS;
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inst_drop();
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}
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void inst_divmod() {
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int a, b;
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a = TOS;
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b = NOS;
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TOS = b / a;
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NOS = b % a;
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}
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void inst_and() {
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NOS = TOS & NOS;
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inst_drop();
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}
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void inst_or() {
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NOS = TOS | NOS;
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inst_drop();
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}
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void inst_xor() {
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NOS = TOS ^ NOS;
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inst_drop();
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}
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void inst_shift() {
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CELL y = TOS;
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CELL x = NOS;
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if (TOS < 0)
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NOS = NOS << (TOS * -1);
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else {
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if (x < 0 && y > 0)
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NOS = x >> y | ~(~0U >> y);
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else
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NOS = x >> y;
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}
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|
inst_drop();
|
|
}
|
|
|
|
void inst_zret() {
|
|
if (TOS == 0) {
|
|
inst_drop();
|
|
ip = TORS;
|
|
rp--;
|
|
}
|
|
}
|
|
|
|
void inst_end() {
|
|
ip = IMAGE_SIZE;
|
|
}
|
|
|
|
typedef void (*Handler)(void);
|
|
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
|
|
};
|
|
|
|
void ngaProcessOpcode(CELL opcode) {
|
|
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 <= 26))
|
|
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(int opcode) {
|
|
ngaProcessOpcode(o1);
|
|
ngaProcessOpcode(o2);
|
|
ngaProcessOpcode(o3);
|
|
ngaProcessOpcode(o4);
|
|
}
|
|
|