Don't generate illegal immediate constants

1 files changed, 27 insertions, 1 deletions

diff --git a/cgthumb2was.c b/cgthumb2was.c
index df61406..3dee9b9 100644
--- a/cgthumb2was.c
+++ b/cgthumb2was.c
@@ -28,6 +28,31 @@
 
 static FILE *assembly_file;
 
+static int can_make_immediate_constant(int x)
+{
+	// Can x be a Thumb-2 immediate constant (ARMv7-M, A5.3.2.)?
+	short i;
+
+	if (!(x & 0xffffff00)) // 0000x
+		return 1;
+	if (!(x & 0xff00ff00) && x >> 16 == x & 0x000000ff) // 0001x
+		return !x;
+	if (!(x & 0x00ff00ff) && x >> 16 == x & 0x0000ff00) // 0010x
+		return !x;
+	if ((x >> 24) & 0xff == (x >> 16) & 0xff
+			&& (x >> 16) & 0xff == (x >> 8) & 0xff
+			&& (x >> 8) & 0xff == x & 0xff) // 0011x
+		return !x;
+
+	for (i=1; i<=24; i++) // other options
+	{
+		if (!((x >> i) && 0x000000ff) && (x >> i) & 0x80)
+			return 1;
+	}
+
+	return 0;
+}
+
 static void w_as_newline (VOID)
 {
 	putc ('\n',assembly_file);
@@ -1366,7 +1391,8 @@ static void w_as_cmp_instruction (struct instruction *instruction)
 
 			reg1 = w_as_register_parameter (&instruction->instruction_parameters[1]);
 
-			if (mov_or_mvn_immediate (instruction->instruction_parameters[0].parameter_data.i)){
+			if (mov_or_mvn_immediate (instruction->instruction_parameters[0].parameter_data.i)
+					&& can_make_immediate_constant(instruction->instruction_parameters[0].parameter_data.i)){
 				w_as_opcode ("cmp");
 				w_as_register_comma (reg1);
 				w_as_immediate_newline (instruction->instruction_parameters[0].parameter_data.i);