diff --git a/makefile b/makefile
index 24e2457..563ad91 100644
--- a/makefile
+++ b/makefile
@@ -1,5 +1,5 @@
 RELEASE_flags=-DNDEBUG -O2 -g0 -s
-DEBUG_flags=-std=c89 -D_POSIX_C_SOURCE=199309L -DDEBUG -Wall -Wno-unknown-pragmas -Wpedantic -Wshadow -Wextra -Werror=implicit-int -Werror=incompatible-pointer-types -Werror=int-conversion -Wvla -g -Og -fsanitize=address -fsanitize=undefined
+DEBUG_flags=-std=c99 -D_POSIX_C_SOURCE=199309L -DDEBUG -Wall -Wno-unknown-pragmas -Wpedantic -Wshadow -Wextra -Werror=implicit-int -Werror=incompatible-pointer-types -Werror=int-conversion -Wvla -g -Og -fsanitize=address -fsanitize=undefined
 
 .PHONY: all debug dest run debug test install uninstall format clean archive
 
diff --git a/src/modal.c b/src/modal.c
index bd87ae0..f3d95ae 100644
--- a/src/modal.c
+++ b/src/modal.c
@@ -44,17 +44,25 @@ static void
 device_write(char *s)
 {
 	int acc = 0;
-	char c = *s, *cap = walk(s), *reg = regs['0'];
-	if(reg) {
+	char c = *s, *cap = walk(s), **reg = regs + '0';
+	/* phase: ALU */
+	if(*reg) {
 		switch(c) {
-		case '+':
-			for(acc = sint(reg++); *reg; reg++) acc = acc + sint(reg);
-			break;
+		/* clang-format off */
+		case '+': for(acc = sint(*reg++); *reg != 0; reg++)  acc += sint(*reg); break;
+		case '-': for(acc = sint(*reg++); *reg != 0; reg++)  acc -= sint(*reg); break;
+		case '*': for(acc = sint(*reg++); *reg != 0; reg++)  acc *= sint(*reg); break;
+		case '/': for(acc = sint(*reg++); *reg != 0; reg++)  acc /= sint(*reg); break;
+		case '%': for(acc = sint(*reg++); *reg != 0; reg++)  acc %= sint(*reg); break;
+		case '&': for(acc = sint(*reg++); *reg != 0; reg++)  acc &= sint(*reg); break;
+		case '^': for(acc = sint(*reg++); *reg != 0; reg++)  acc ^= sint(*reg); break;
+		case '|': for(acc = sint(*reg++); *reg != 0; reg++)  acc |= sint(*reg); break;
+			/* clang-format on */
 		}
-		dst_ += snprintf(dst_, 0x10, "%d\n", acc);
+		dst_ += snprintf(dst_, 0x10, "%d", acc);
 		return;
 	}
-
+	/* phase: string */
 	if(*s == '(') s++, --cap;
 	while(s < cap) {
 		c = *s++;
@@ -70,7 +78,7 @@ device_write(char *s)
 }
 
 static void
-device_read(char *s)
+device_read(void)
 {
 	char c;
 	while(fread(&c, 1, 1, stdin) && c >= ' ')
@@ -90,7 +98,7 @@ write_reg(char r, char *reg)
 		return;
 	case '<': /* op: input */
 	case '~':
-		device_read(reg);
+		device_read();
 		return;
 	case '^': /* op: join */
 		if(*reg == '(') reg++, --cap;