From d79898fa201b334766d853fea9b0be1a4dedc7ca Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ond=C5=99ej=20Hru=C5=A1ka?= <ondra@ondrovo.com>
Date: Mon, 15 Nov 2021 23:25:56 +0100
Subject: [PATCH] remove some direct access to stack arrays

---
 include/fh_config.h |  4 +---
 src/fh_builtins.c   | 44 +++++++++++++++++++++++++-------------------
 src/fh_stack.c      |  2 ++
 3 files changed, 28 insertions(+), 22 deletions(-)

diff --git a/include/fh_config.h b/include/fh_config.h
index e451208..4c8bf3d 100644
--- a/include/fh_config.h
+++ b/include/fh_config.h
@@ -7,14 +7,12 @@
 #ifndef FORTH_FH_CONFIG_H
 #define FORTH_FH_CONFIG_H
 
-#define CONTROL_STACK_DEPTH 1024
 #define DATA_STACK_DEPTH 1024
 #define RETURN_STACK_DEPTH 1024
 #define MAX_NAME_LEN 32
-#define DICT_SIZE 1024
 #define HEAP_SIZE (1024*1024)
 #define MAXLINE 65535
-#define PAD_OFFSET 340
+#define PAD_OFFSET 340 // why? copied from somewhere
 #define WORDBUF_SIZE 128
 #define INPUT_BUFFER_SIZE 256
 
diff --git a/src/fh_builtins.c b/src/fh_builtins.c
index 673df8a..88ec39d 100644
--- a/src/fh_builtins.c
+++ b/src/fh_builtins.c
@@ -538,18 +538,17 @@ static enum fh_error w_two_swap(struct fh_thread_s *fh, const struct fh_word_s *
 {
   (void) w;
   enum fh_error rv;
-  if (fh->data_stack_top < 4) {
-    LOG("DS two-swap UNDERFLOW");
-    return FH_ERR_DS_UNDERFLOW;
-  }
 
-  uint32_t n = fh->data_stack_top - 4;
-  uint32_t a = fh->data_stack[n];
-  uint32_t b = fh->data_stack[n + 1];
-  fh->data_stack[n] = fh->data_stack[n + 2];
-  fh->data_stack[n + 1] = fh->data_stack[n + 3];
-  fh->data_stack[n + 2] = a;
-  fh->data_stack[n + 3] = b;
+  uint32_t a, b, c, d;
+  TRY(ds_pop(fh, &a));
+  TRY(ds_pop(fh, &b));
+  TRY(ds_pop(fh, &c));
+  TRY(ds_pop(fh, &d));
+
+  TRY(ds_push(fh, b));
+  TRY(ds_push(fh, a));
+  TRY(ds_push(fh, d));
+  TRY(ds_push(fh, c));
   return FH_OK;
 }
 
@@ -719,14 +718,6 @@ static enum fh_error wp_putc(struct fh_thread_s *fh, const struct fh_word_s *w)
   return FH_OK;
 }
 
-static enum fh_error w_space(struct fh_thread_s *fh, const struct fh_word_s *w)
-{
-  (void) w;
-  (void) fh;
-  FHPRINT(" ");
-  return FH_OK;
-}
-
 static enum fh_error w_debug_dump(struct fh_thread_s *fh, const struct fh_word_s *w)
 {
   (void) w;
@@ -996,6 +987,20 @@ static enum fh_error w_see(struct fh_thread_s *fh, const struct fh_word_s *w)
   return FH_OK;
 }
 
+static enum fh_error w_pad(struct fh_thread_s *fh, const struct fh_word_s *w)
+{
+  (void) w;
+  enum fh_error rv;
+  uint32_t addr = fh->here + PAD_OFFSET;
+  if (addr + 84 >= HEAP_SIZE) {
+    LOGE("Heap overflow, PAD is too small!");
+    return FH_ERR_HEAP_FULL;
+  }
+
+  TRY(ds_push(fh, addr));
+  return FH_OK;
+}
+
 static enum fh_error wp_const(struct fh_thread_s *fh, const struct fh_word_s *w)
 {
   enum fh_error rv;
@@ -1177,6 +1182,7 @@ enum fh_error register_builtin_words(struct fh_thread_s *fh)
       {"hex",       wp_setbase,        0, 16},
       {"base",      wp_const,          0, MAGICADDR_BASE},
       {"here",      wp_const,          0, MAGICADDR_HERE},
+      {"pad",       w_pad,             0, 0},
       {"false",     wp_const,          0, 0},
       {"true",      wp_const,          0, 0xFFFFFFFF},
       {"+",         w_plus,            0, 0},
diff --git a/src/fh_stack.c b/src/fh_stack.c
index 449b2ea..19ba599 100644
--- a/src/fh_stack.c
+++ b/src/fh_stack.c
@@ -4,6 +4,8 @@
 #include "fh_stack.h"
 #include "fh_print.h"
 
+// TODO stacks should grow down, not up!
+
 enum fh_error ds_roll(struct fh_thread_s *fh, int n)
 {
   if (fh->data_stack_top <= n) {