Index: exec.c
==================================================================
--- exec.c
+++ exec.c
@@ -11,17 +11,140 @@
 #include "sqlite3.h"
 #include "smallxrm.h"
 #include "heromesh.h"
 
 Uint32 generation_number;
-Object*objects;
+Object**objects;
 Uint32 nobjects;
 Value globals[0x800];
+Uint32 firstobj=VOIDLINK;
+Uint32 lastobj=VOIDLINK;
+Uint32 playfield[64*64];
+
+typedef struct {
+  Uint16 msg;
+  Uint32 from;
+  Value arg1,arg2,arg3;
+} MessageVars;
 
 static jmp_buf my_env;
-static int my_error;
+static const char*my_error;
+static MessageVars msgvars;
+static char lastimage_processing;
+
+#define Throw(x) (my_error=(x),longjmp(my_env,1))
+#define StackReq(x,y)
+
+void pfunlink(Uint32 n) {
+  Object*o=objects[n];
+  if(o->down==VOIDLINK) playfield[o->x+o->y*64-65]=o->up;
+  else objects[o->down]->up=o->up;
+  if(o->up!=VOIDLINK) objects[o->up]->down=o->down;
+  o->down=o->up=VOIDLINK;
+}
+
+void pflink(Uint32 n) {
+  Object*o=objects[n];
+  int p=o->x+o->y*64-65;
+  if(p<0) return;
+  if(playfield[p]==VOIDLINK) {
+    playfield[p]=n;
+  } else {
+    Sint32 d=o->density;
+    Uint32 m=playfield[p];
+    Uint32 t=VOIDLINK;
+    while(m!=VOIDLINK && objects[m]->density>=d) t=m,m=objects[m]->up;
+    o->down=t;
+    o->up=m;
+    if(t!=VOIDLINK) objects[t]->up=n; else playfield[p]=n;
+    if(m!=VOIDLINK) objects[m]->down=n;
+  }
+}
+
+#define OBJECT_ARRAY_BLOCK 256
+Uint32 objalloc(Uint16 c) {
+  // c must be a valid (nonzero) class number, and not a class with CF_GROUP, CF_NOCLASS1, or CF_NOCLASS2 flags.
+  Uint32 n;
+  Class*cl=classes[c];
+  Object*o=calloc(1,sizeof(Object)+cl->uservars*sizeof(Value));
+  if(!o) fatal("Allocation failed\n");
+  o->class=c;
+  o->generation=generation_number;
+#define C(x) o->x=cl->x;
+  C(height) C(weight) C(climb) C(density) C(volume) C(strength) C(arrivals) C(departures) C(temperature)
+  C(shape) C(shovable) C(oflags)
+  C(sharp[0]) C(sharp[1]) C(sharp[2]) C(sharp[3])
+  C(hard[0]) C(hard[1]) C(hard[2]) C(hard[3])
+#undef C
+  o->misc4=NVALUE(cl->misc4);
+  o->misc5=NVALUE(cl->misc5);
+  o->misc6=NVALUE(cl->misc6);
+  o->misc7=NVALUE(cl->misc7);
+  if(nobjects) for(n=nobjects-1;;n--) {
+    if(!objects[n]) goto found;
+    if(!n) break;
+  }
+  if(nobjects>=0xFFFF0000L) fatal("Too many objects\n");
+  objects=realloc(objects,(nobjects+OBJECT_ARRAY_BLOCK)*sizeof(Object*));
+  if(!objects) fatal("Allocation failed\n");
+  for(n=nobjects;n<nobjects+OBJECT_ARRAY_BLOCK;n++) objects[n]=0;
+  n=nobjects;
+  nobjects+=OBJECT_ARRAY_BLOCK;
+  found:
+  o->up=o->down=o->prev=o->next=VOIDLINK;
+  if(cl->nmsg || classes[0]->nmsg) {
+    o->prev=lastobj;
+    if(lastobj!=VOIDLINK) objects[lastobj]->next=n;
+    lastobj=n;
+    if(firstobj==VOIDLINK) firstobj=n;
+  }
+  objects[n]=o;
+  return n;
+}
+
+static void execute_program(Uint16*code,int ptr,Uint32 obj) {
+  Object*o=objects[obj];
+  if(StackProtection()) Throw("Call stack overflow");
+  for(;;) switch(code[ptr++]) {
+    case OP_GOTO: ptr=code[ptr]; break;
+    case OP_CALLSUB: execute_program(code,code[ptr++],obj); break;
+    case OP_RET: return;
+    default: Throw("Internal error: Unrecognized opcode");
+  }
+}
+
+static Value send_message(Uint32 from,Uint32 to,Uint16 msg,Value arg1,Value arg2,Value arg3) {
+  MessageVars saved=msgvars;
+  Uint16 c=classes[objects[to]->class];
+  Uint16 p=get_message_ptr(c,msg);
+  Uint16*code;
+  if(p==0xFFFF) {
+    p=get_message_ptr(0,msg);
+    if(!p) return NVALUE(0);
+    code=classes[0]->codes;
+  } else {
+    code=classes[c]->codes;
+  }
+  
+  msgvars={msg,from,arg1,arg2,arg3};
+  execute_program(code,p,to);
+  msgvars=saved;
+  
+}
+
+void annihilate(void) {
+  Uint32 i;
+  if(!objects) return;
+  for(i=0;i<nobjects;i++) free(objects[i]);
+  nobjects=0;
+  free(objects);
+  objects=0;
+  firstobj=lastobj=VOIDLINK;
+  for(i=0;i<64*64;i++) playfield[i]=VOIDLINK;
+}
 
-int execute_turn(int key) {
+const char*execute_turn(int key) {
   if(setjmp(my_env)) return my_error;
+  lastimage_processing=0;
   
   return 0;
 }

Index: heromesh.h
==================================================================
--- heromesh.h
+++ heromesh.h
@@ -27,10 +27,11 @@
 #define SVALUE(x,y) ((Value){.s=x,.t=y})
 #define NVALUE(x) SVALUE(x,TY_NUMBER)
 #define CVALUE(x) UVALUE(x,TY_CLASS)
 #define MVALUE(x) UVALUE(x,TY_MESSAGE)
 #define ZVALUE(x) UVALUE(x,TY_STRING)
+#define OVALUE(x) UVALUE(x,objects[x]->generation)
 
 #define N_MESSAGES 23
 extern const char*const standard_message_names[];
 extern const char*const standard_sound_names[];
 extern const char*const heromesh_key_names[256];
@@ -144,26 +145,37 @@
 // == function ==
 
 void init_sql_functions(sqlite3_int64*ptr0,sqlite3_int64*ptr1);
 
 // == exec ==
+
+#define VOIDLINK ((Uint32)(-1))
 
 // The following "internal object flags" are part of the "dir" variable:
 #define IOF_DEAD 0x10 // object doesn't exist, except to continue an animation
 #define IOF_ANIM 0x20 // an animation is being displayed
 
 typedef struct {
   Sint32 height,weight,climb,density,volume,strength,arrivals,departures,temperature;
-  Uint32 arrived,departed,arrived2,departed2,generation,up;
+  Uint32 arrived,departed,arrived2,departed2,generation;
+  Uint32 up,down,prev,next; // links to other objects
   Uint16 class,oflags;
   Uint16 sharp[4];
   Uint16 hard[4];
   Uint8 x,y,shape,shovable,image,dir;
   Value misc1,misc2,misc3,misc4,misc5,misc6,misc7;
   Value uservars[0];
 } Object;
 
 extern Uint32 generation_number;
-extern Object*objects;
+extern Object**objects;
 extern Uint32 nobjects;
 extern Value globals[0x800];
+extern Uint32 firstobj,lastobj;
+extern Uint32 playfield[64*64];
+
+void pfunlink(Uint32 n);
+void pflink(Uint32 n);
+Uint32 objalloc(Uint16 c);
+void annihilate(void);
+const char*execute_turn(int key);