@@ -72,9 +72,15 @@ pop_push = function(k, n, s)

     return nil

   end

 end

+local indented_block

+indented_block = function(s)

+  s = s:gsub('^%{ *', '{\n'):gsub('\n', '\n\t'):gsub('\t%} *$', '}\n')

+  s = s:gsub('\n[^\n]+%.error = [^\n]+', '%0\n#ifndef NO_STACK_CHECKS\n\tgoto error;\n#endif')

+  return s

+end

 local process

 process = function(body)

-  local out_body = body:gsub('^%{ *', ''):gsub(' *%}$', ''):gsub('; ', ';\n'):gsub('(%a+)(%d+)(%b())', pop_push)

+  local out_body = body:gsub('^%{ *', ''):gsub(' *%}$', ''):gsub('; ', ';\n'):gsub('%b{} *', indented_block):gsub('(%a+)(%d+)(%b())', pop_push)

   local in_ifdef = false

   local _list_0 = {

     'src',

@@ -132,6 +138,8 @@ for l in assert(io.lines('src/uxn.c')) do

     if replacements[name] then

       body = replacements[name]

     end

+    body = body:gsub('u%-%>src%-%>', 'src.')

+    body = body:gsub('u%-%>dst%-%>', 'dst.')

     body = body:gsub('u%-%>src', 'src')

     body = body:gsub('u%-%>dst', 'dst')

     top = {

@@ -278,6 +286,7 @@ See etc/mkuxn-fast.moon for instructions.

 */

 ]])

+  wanted = true

   while true do

     local _continue_0 = false

     repeat

@@ -287,9 +296,19 @@ See etc/mkuxn-fast.moon for instructions.

         break

       end

       if l == '/* Stack */' then

+        wanted = false

+      end

+      if l:match('errors%[%]') then

+        _with_0:write('\n#ifndef NO_STACK_CHECKS\n')

+        wanted = true

+      end

+      if wanted then

+        _with_0:write(('%s\n'):format(l))

+      end

+      if l == '}' then

+        _with_0:write('#endif\n\n')

         break

       end

-      _with_0:write(('%s\n'):format(l))

       _continue_0 = true

     until true

     if not _continue_0 then

@@ -338,12 +357,10 @@ evaluxn(Uxn *u, Uint16 vec)

 	return 1;

 #ifndef NO_STACK_CHECKS

 error:

-	printf("Halted: %s-stack %sflow#%04x, at 0x%04x\n",

-		u->wst.error ? "Working" : "Return",

-		((u->wst.error | u->rst.error) & 2) ? "over" : "under",

-		instr,

-		u->ram.ptr);

-	return 0;

+	if(u->wst.error)

+		return haltuxn(u, u->wst.error, "Working-stack", instr);

+	else

+		return haltuxn(u, u->rst.error, "Return-stack", instr);

 #endif

 }

@@ -77,8 +77,13 @@ pop_push = (k, n, s) ->

 		else

 			nil

+indented_block = (s) ->

+	s = s\gsub('^%{ *', '{\n')\gsub('\n', '\n\t')\gsub('\t%} *$', '}\n')

+	s = s\gsub('\n[^\n]+%.error = [^\n]+', '%0\n#ifndef NO_STACK_CHECKS\n\tgoto error;\n#endif')

+	s

+

 process = (body) ->

-	out_body = body\gsub('^%{ *', '')\gsub(' *%}$', '')\gsub('; ', ';\n')\gsub '(%a+)(%d+)(%b())', pop_push

+	out_body = body\gsub('^%{ *', '')\gsub(' *%}$', '')\gsub('; ', ';\n')\gsub('%b{} *', indented_block)\gsub '(%a+)(%d+)(%b())', pop_push

 	in_ifdef = false

 	for k in *{'src', 'dst'}

 		if bottom[k] != 0

@@ -115,6 +120,8 @@ for l in assert io.lines 'src/uxn.c'

 		continue

 	if replacements[name]

 		body = replacements[name]

+	body = body\gsub 'u%-%>src%-%>', 'src.'

+	body = body\gsub 'u%-%>dst%-%>', 'dst.'

 	body = body\gsub 'u%-%>src', 'src'

 	body = body\gsub 'u%-%>dst', 'dst'

 	top = { src: 0, dst: 0 }

@@ -200,13 +207,21 @@ See etc/mkuxn-fast.moon for instructions.

 */

 ]]

+	wanted = true

 	while true

 		l = f\read '*l'

 		if l\match' push' or l\match'[ *]pop'

 			continue

 		if l == '/* Stack */'

+			wanted = false

+		if l\match 'errors%[%]'

+			\write '\n#ifndef NO_STACK_CHECKS\n'

+			wanted = true

+		if wanted

+			\write '%s\n'\format l

+		if l == '}'

+			\write '#endif\n\n'

 			break

-		\write '%s\n'\format l

 	\write [[

 /* clang-format on */

@@ -238,12 +253,10 @@ evaluxn(Uxn *u, Uint16 vec)

 	return 1;

 #ifndef NO_STACK_CHECKS

 error:

-	printf("Halted: %s-stack %sflow#%04x, at 0x%04x\n",

-		u->wst.error ? "Working" : "Return",

-		((u->wst.error | u->rst.error) & 2) ? "over" : "under",

-		instr,

-		u->ram.ptr);

-	return 0;

+	if(u->wst.error)

+		return haltuxn(u, u->wst.error, "Working-stack", instr);

+	else

+		return haltuxn(u, u->rst.error, "Return-stack", instr);

 #endif

 }

@@ -34,6 +34,19 @@ void   mempoke16(Uint8 *m, Uint16 a, Uint16 b) { mempoke8(m, a, b >> 8); mempoke

 Uint16 mempeek16(Uint8 *m, Uint16 a) { return (mempeek8(m, a) << 8) + mempeek8(m, a + 1); }

 void   devpoke16(Device *d, Uint8 a, Uint16 b) { devpoke8(d, a, b >> 8); devpoke8(d, a + 1, b); }

 Uint16 devpeek16(Device *d, Uint16 a) { return (devpeek8(d, a) << 8) + devpeek8(d, a + 1); }

+

+#ifndef NO_STACK_CHECKS

+static const char *errors[] = {"underflow", "overflow", "division by zero"};

+

+int

+haltuxn(Uxn *u, Uint8 error, char *name, int id)

+{

+	printf("Halted: %s %s#%04x, at 0x%04x\n", name, errors[error - 1], id, u->ram.ptr);

+	u->ram.ptr = 0;

+	return 0;

+}

+#endif

+

 /* clang-format on */

 #pragma mark - Core

@@ -453,6 +466,13 @@ evaluxn(Uxn *u, Uint16 vec)

 			__asm__("evaluxn_1b_DIV:");

 			{

 				Uint8 a = u->wst.dat[u->wst.ptr - 1], b = u->wst.dat[u->wst.ptr - 2];

+				if(a == 0) {

+					u->wst.error = 3;

+#ifndef NO_STACK_CHECKS

+					goto error;

+#endif

+					a = 1;

+				}

 				u->wst.dat[u->wst.ptr - 2] = b / a;

 #ifndef NO_STACK_CHECKS

 				if(__builtin_expect(u->wst.ptr < 2, 0)) {

@@ -926,6 +946,13 @@ evaluxn(Uxn *u, Uint16 vec)

 			__asm__("evaluxn_3b_DIV2:");

 			{

 				Uint16 a = (u->wst.dat[u->wst.ptr - 1] | (u->wst.dat[u->wst.ptr - 2] << 8)), b = (u->wst.dat[u->wst.ptr - 3] | (u->wst.dat[u->wst.ptr - 4] << 8));

+				if(a == 0) {

+					u->wst.error = 3;

+#ifndef NO_STACK_CHECKS

+					goto error;

+#endif

+					a = 1;

+				}

 				u->wst.dat[u->wst.ptr - 4] = (b / a) >> 8;

 				u->wst.dat[u->wst.ptr - 3] = (b / a) & 0xff;

 #ifndef NO_STACK_CHECKS

@@ -1376,6 +1403,13 @@ evaluxn(Uxn *u, Uint16 vec)

 			__asm__("evaluxn_5b_DIVr:");

 			{

 				Uint8 a = u->rst.dat[u->rst.ptr - 1], b = u->rst.dat[u->rst.ptr - 2];

+				if(a == 0) {

+					u->rst.error = 3;

+#ifndef NO_STACK_CHECKS

+					goto error;

+#endif

+					a = 1;

+				}

 				u->rst.dat[u->rst.ptr - 2] = b / a;

 #ifndef NO_STACK_CHECKS

 				if(__builtin_expect(u->rst.ptr < 2, 0)) {

@@ -1849,6 +1883,13 @@ evaluxn(Uxn *u, Uint16 vec)

 			__asm__("evaluxn_7b_DIV2r:");

 			{

 				Uint16 a = (u->rst.dat[u->rst.ptr - 1] | (u->rst.dat[u->rst.ptr - 2] << 8)), b = (u->rst.dat[u->rst.ptr - 3] | (u->rst.dat[u->rst.ptr - 4] << 8));

+				if(a == 0) {

+					u->rst.error = 3;

+#ifndef NO_STACK_CHECKS

+					goto error;

+#endif

+					a = 1;

+				}

 				u->rst.dat[u->rst.ptr - 4] = (b / a) >> 8;

 				u->rst.dat[u->rst.ptr - 3] = (b / a) & 0xff;

 #ifndef NO_STACK_CHECKS

@@ -2332,6 +2373,13 @@ evaluxn(Uxn *u, Uint16 vec)

 			__asm__("evaluxn_9b_DIVk:");

 			{

 				Uint8 a = u->wst.dat[u->wst.ptr - 1], b = u->wst.dat[u->wst.ptr - 2];

+				if(a == 0) {

+					u->wst.error = 3;

+#ifndef NO_STACK_CHECKS

+					goto error;

+#endif

+					a = 1;

+				}

 				u->wst.dat[u->wst.ptr] = b / a;

 #ifndef NO_STACK_CHECKS

 				if(__builtin_expect(u->wst.ptr < 2, 0)) {

@@ -2846,6 +2894,13 @@ evaluxn(Uxn *u, Uint16 vec)

 			__asm__("evaluxn_bb_DIV2k:");

 			{

 				Uint16 a = (u->wst.dat[u->wst.ptr - 1] | (u->wst.dat[u->wst.ptr - 2] << 8)), b = (u->wst.dat[u->wst.ptr - 3] | (u->wst.dat[u->wst.ptr - 4] << 8));

+				if(a == 0) {

+					u->wst.error = 3;

+#ifndef NO_STACK_CHECKS

+					goto error;

+#endif

+					a = 1;

+				}

 				u->wst.dat[u->wst.ptr] = (b / a) >> 8;

 				u->wst.dat[u->wst.ptr + 1] = (b / a) & 0xff;

 #ifndef NO_STACK_CHECKS

@@ -3349,6 +3404,13 @@ evaluxn(Uxn *u, Uint16 vec)

 			__asm__("evaluxn_db_DIVkr:");

 			{

 				Uint8 a = u->rst.dat[u->rst.ptr - 1], b = u->rst.dat[u->rst.ptr - 2];

+				if(a == 0) {

+					u->rst.error = 3;

+#ifndef NO_STACK_CHECKS

+					goto error;

+#endif

+					a = 1;

+				}

 				u->rst.dat[u->rst.ptr] = b / a;

 #ifndef NO_STACK_CHECKS

 				if(__builtin_expect(u->rst.ptr < 2, 0)) {

@@ -3863,6 +3925,13 @@ evaluxn(Uxn *u, Uint16 vec)

 			__asm__("evaluxn_fb_DIV2kr:");

 			{

 				Uint16 a = (u->rst.dat[u->rst.ptr - 1] | (u->rst.dat[u->rst.ptr - 2] << 8)), b = (u->rst.dat[u->rst.ptr - 3] | (u->rst.dat[u->rst.ptr - 4] << 8));

+				if(a == 0) {

+					u->rst.error = 3;

+#ifndef NO_STACK_CHECKS

+					goto error;

+#endif

+					a = 1;

+				}

 				u->rst.dat[u->rst.ptr] = (b / a) >> 8;

 				u->rst.dat[u->rst.ptr + 1] = (b / a) & 0xff;

 #ifndef NO_STACK_CHECKS

@@ -3961,12 +4030,10 @@ evaluxn(Uxn *u, Uint16 vec)

 	return 1;

 #ifndef NO_STACK_CHECKS

 error:

-	printf("Halted: %s-stack %sflow#%04x, at 0x%04x\n",

-		u->wst.error ? "Working" : "Return",

-		((u->wst.error | u->rst.error) & 2) ? "over" : "under",

-		instr,

-		u->ram.ptr);

-	return 0;

+	if(u->wst.error)

+		return haltuxn(u, u->wst.error, "Working-stack", instr);

+	else

+		return haltuxn(u, u->rst.error, "Return-stack", instr);

 #endif

 }

@@ -61,7 +61,7 @@ void op_deo(Uxn *u) { Uint8 a = pop8(u->src), b = pop8(u->src); devpoke8(&u->dev

 void op_add(Uxn *u) { Uint8 a = pop8(u->src), b = pop8(u->src); push8(u->src, b + a); }

 void op_sub(Uxn *u) { Uint8 a = pop8(u->src), b = pop8(u->src); push8(u->src, b - a); }

 void op_mul(Uxn *u) { Uint8 a = pop8(u->src), b = pop8(u->src); push8(u->src, b * a); }

-void op_div(Uxn *u) { Uint8 a = pop8(u->src), b = pop8(u->src); push8(u->src, b / a); }

+void op_div(Uxn *u) { Uint8 a = pop8(u->src), b = pop8(u->src); if(a == 0) { u->src->error = 3; a = 1; } push8(u->src, b / a); }

 void op_and(Uxn *u) { Uint8 a = pop8(u->src), b = pop8(u->src); push8(u->src, b & a); }

 void op_ora(Uxn *u) { Uint8 a = pop8(u->src), b = pop8(u->src); push8(u->src, b | a); }

 void op_eor(Uxn *u) { Uint8 a = pop8(u->src), b = pop8(u->src); push8(u->src, b ^ a); }

@@ -95,7 +95,7 @@ void op_deo16(Uxn *u) { Uint8 a = pop8(u->src); Uint16 b = pop16(u->src); devpok

 void op_add16(Uxn *u) { Uint16 a = pop16(u->src), b = pop16(u->src); push16(u->src, b + a); }

 void op_sub16(Uxn *u) { Uint16 a = pop16(u->src), b = pop16(u->src); push16(u->src, b - a); }

 void op_mul16(Uxn *u) { Uint16 a = pop16(u->src), b = pop16(u->src); push16(u->src, b * a); }

-void op_div16(Uxn *u) { Uint16 a = pop16(u->src), b = pop16(u->src); push16(u->src, b / a); }

+void op_div16(Uxn *u) { Uint16 a = pop16(u->src), b = pop16(u->src); if(a == 0) { u->src->error = 3; a = 1; } push16(u->src, b / a); }

 void op_and16(Uxn *u) { Uint16 a = pop16(u->src), b = pop16(u->src); push16(u->src, b & a); }

 void op_ora16(Uxn *u) { Uint16 a = pop16(u->src), b = pop16(u->src); push16(u->src, b | a); }

 void op_eor16(Uxn *u) { Uint16 a = pop16(u->src), b = pop16(u->src); push16(u->src, b ^ a); }

@@ -117,10 +117,12 @@ void (*ops[])(Uxn *u) = {

 #pragma mark - Core

+static const char *errors[] = {"underflow", "overflow", "division by zero"};

+

 int

-haltuxn(Uxn *u, char *name, int id)

+haltuxn(Uxn *u, Uint8 error, char *name, int id)

 {

-	printf("Halted: %s#%04x, at 0x%04x\n", name, id, u->ram.ptr);

+	printf("Halted: %s %s#%04x, at 0x%04x\n", name, errors[error - 1], id, u->ram.ptr);

 	u->ram.ptr = 0;

 	return 0;

 }

@@ -145,9 +147,9 @@ stepuxn(Uxn *u, Uint8 instr)

 {

 	opcuxn(u, instr);

 	if(u->wst.error)

-		return haltuxn(u, u->wst.error == 1 ? "Working-stack underflow" : "Working-stack overflow", instr);

+		return haltuxn(u, u->wst.error, "Working-stack", instr);

 	if(u->rst.error)

-		return haltuxn(u, u->rst.error == 1 ? "Return-stack underflow" : "Return-stack overflow", instr);

+		return haltuxn(u, u->rst.error, "Return-stack", instr);

 	return 1;

 }