jumps in 'for' loops don't need to be signed

lopcodes.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lopcodes.c,v 1.58 2017/04/28 20:57:45 roberto Exp roberto $
+** $Id: lopcodes.c,v 1.59 2017/06/29 15:38:41 roberto Exp roberto $
 ** Opcodes for Lua virtual machine
 ** See Copyright Notice in lua.h
 */
@@ -124,10 +124,10 @@ LUAI_DDEF const lu_byte luaP_opmodes[NUM_OPCODES] = {
  ,opmode(0, 1, OpArgU, OpArgU, iABC)		/* OP_CALL */
  ,opmode(0, 1, OpArgU, OpArgU, iABC)		/* OP_TAILCALL */
  ,opmode(0, 0, OpArgU, OpArgN, iABC)		/* OP_RETURN */
- ,opmode(0, 1, OpArgR, OpArgN, iAsBx)		/* OP_FORLOOP */
- ,opmode(0, 1, OpArgR, OpArgN, iAsBx)		/* OP_FORPREP */
+ ,opmode(0, 1, OpArgR, OpArgN, iABx)		/* OP_FORLOOP */
+ ,opmode(0, 1, OpArgR, OpArgN, iABx)		/* OP_FORPREP */
  ,opmode(0, 0, OpArgN, OpArgU, iABC)		/* OP_TFORCALL */
- ,opmode(0, 1, OpArgR, OpArgN, iAsBx)		/* OP_TFORLOOP */
+ ,opmode(0, 1, OpArgR, OpArgN, iABx)		/* OP_TFORLOOP */
  ,opmode(0, 0, OpArgU, OpArgU, iABC)		/* OP_SETLIST */
  ,opmode(0, 1, OpArgU, OpArgN, iABx)		/* OP_CLOSURE */
  ,opmode(0, 1, OpArgU, OpArgR, iABC)		/* OP_VARARG */

lopcodes.h

@@ -1,5 +1,5 @@
 /*
-** $Id: lopcodes.h,v 1.154 2017/05/08 16:08:01 roberto Exp roberto $
+** $Id: lopcodes.h,v 1.155 2017/06/29 15:38:41 roberto Exp roberto $
 ** Opcodes for Lua virtual machine
 ** See Copyright Notice in lua.h
 */
@@ -229,12 +229,12 @@ OP_CALL,/*	A B C	R(A), ... ,R(A+C-2) := R(A)(R(A+1), ... ,R(A+B-1)) */
 OP_TAILCALL,/*	A B C	return R(A)(R(A+1), ... ,R(A+B-1))		*/
 OP_RETURN,/*	A B	return R(A), ... ,R(A+B-2)	(see note)	*/
 
-OP_FORLOOP,/*	A sBx	R(A)+=R(A+2);
-			if R(A) <?= R(A+1) then { pc+=sBx; R(A+3)=R(A) }*/
-OP_FORPREP,/*	A sBx	R(A)-=R(A+2); pc+=sBx				*/
+OP_FORLOOP,/*	A Bx	R(A)+=R(A+2);
+			if R(A) <?= R(A+1) then { pc-=Bx; R(A+3)=R(A) }*/
+OP_FORPREP,/*	A Bx	R(A)-=R(A+2); pc+=Bx				*/
 
 OP_TFORCALL,/*	A C	R(A+3), ... ,R(A+2+C) := R(A)(R(A+1), R(A+2));	*/
-OP_TFORLOOP,/*	A sBx	if R(A+1) ~= nil then { R(A)=R(A+1); pc += sBx }*/
+OP_TFORLOOP,/*	A Bx	if R(A+1) ~= nil then { R(A)=R(A+1); pc -= Bx }*/
 
 OP_SETLIST,/*	A B C	R(A)[(C-1)*FPF+i] := R(A+i), 1 <= i <= B	*/
 

lparser.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lparser.c,v 2.162 2017/06/29 15:38:41 roberto Exp roberto $
+** $Id: lparser.c,v 2.163 2017/08/12 13:12:21 roberto Exp roberto $
 ** Lua Parser
 ** See Copyright Notice in lua.h
 */
@@ -1307,6 +1307,22 @@ static int exp1 (LexState *ls) {
 }
 
 
+/*
+** Fix for instruction at position 'pc' to jump to 'dest'.
+** (Jump addresses are relative in Lua). 'back' true means
+** a back jump.
+*/
+static void fixforjump (FuncState *fs, int pc, int dest, int back) {
+  Instruction *jmp = &fs->f->code[pc];
+  int offset = dest - (pc + 1);
+  if (back)
+    offset = -offset;
+  if (offset > MAXARG_Bx)
+    luaX_syntaxerror(fs->ls, "control structure too long");
+  SETARG_Bx(*jmp, offset);
+}
+
+
 static void forbody (LexState *ls, int base, int line, int nvars, int isnum) {
   /* forbody -> DO block */
   BlockCnt bl;
@@ -1314,21 +1330,23 @@ static void forbody (LexState *ls, int base, int line, int nvars, int isnum) {
   int prep, endfor;
   adjustlocalvars(ls, 3);  /* control variables */
   checknext(ls, TK_DO);
-  prep = isnum ? luaK_codeAsBx(fs, OP_FORPREP, base, NO_JUMP) : luaK_jump(fs);
+  prep = isnum ? luaK_codeABx(fs, OP_FORPREP, base, 0) : luaK_jump(fs);
   enterblock(fs, &bl, 0);  /* scope for declared variables */
   adjustlocalvars(ls, nvars);
   luaK_reserveregs(fs, nvars);
   block(ls);
   leaveblock(fs);  /* end of scope for declared variables */
-  luaK_patchtohere(fs, prep);
-  if (isnum)  /* numeric for? */
-    endfor = luaK_codeAsBx(fs, OP_FORLOOP, base, NO_JUMP);
+  if (isnum) {  /* numeric for? */
+    fixforjump(fs, prep, luaK_getlabel(fs), 0);
+    endfor = luaK_codeABx(fs, OP_FORLOOP, base, 0);
+  }
   else {  /* generic for */
+    luaK_patchtohere(fs, prep);
     luaK_codeABC(fs, OP_TFORCALL, base, 0, nvars);
     luaK_fixline(fs, line);
     endfor = luaK_codeAsBx(fs, OP_TFORLOOP, base + 2, NO_JUMP);
   }
-  luaK_patchlist(fs, endfor, prep + 1);
+  fixforjump(fs, endfor, prep + 1, 1);
   luaK_fixline(fs, line);
 }
 

lvm.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lvm.c,v 2.289 2017/06/29 15:38:41 roberto Exp roberto $
+** $Id: lvm.c,v 2.290 2017/07/07 16:34:32 roberto Exp roberto $
 ** Lua virtual machine
 ** See Copyright Notice in lua.h
 */
@@ -1335,7 +1335,7 @@ void luaV_execute (lua_State *L) {
           lua_Integer idx = intop(+, ivalue(s2v(ra)), step); /* increment index */
           lua_Integer limit = ivalue(s2v(ra + 1));
           if ((0 < step) ? (idx <= limit) : (limit <= idx)) {
-            pc += GETARG_sBx(i);  /* jump back */
+            pc -= GETARG_Bx(i);  /* jump back */
             chgivalue(s2v(ra), idx);  /* update internal index... */
             setivalue(s2v(ra + 3), idx);  /* ...and external index */
           }
@@ -1347,7 +1347,7 @@ void luaV_execute (lua_State *L) {
           idx = luai_numadd(L, idx, step);  /* inc. index */
           if (luai_numlt(0, step) ? luai_numle(idx, limit)
                                   : luai_numle(limit, idx)) {
-            pc += GETARG_sBx(i);  /* jump back */
+            pc -= GETARG_Bx(i);  /* jump back */
             chgfltvalue(s2v(ra), idx);  /* update internal index... */
             setfltvalue(s2v(ra + 3), idx);  /* ...and external index */
           }
@@ -1381,7 +1381,7 @@ void luaV_execute (lua_State *L) {
             luaG_runerror(L, "'for' initial value must be a number");
           setfltvalue(init, luai_numsub(L, ninit, nstep));
         }
-        pc += GETARG_sBx(i);
+        pc += GETARG_Bx(i);
         vmbreak;
       }
       vmcase(OP_TFORCALL) {
@@ -1401,7 +1401,7 @@ void luaV_execute (lua_State *L) {
         l_tforloop:
         if (!ttisnil(s2v(ra + 1))) {  /* continue loop? */
           setobjs2s(L, ra, ra + 1);  /* save control variable */
-          pc += GETARG_sBx(i);  /* jump back */
+          pc -= GETARG_Bx(i);  /* jump back */
         }
         vmbreak;
       }