3 files changed, 111 insertions, 13 deletions
diff --git a/subx/022check_instruction.cc b/subx/022check_instruction.cc
index a1852d84..44b34a60 100644
--- a/subx/022check_instruction.cc
+++ b/subx/022check_instruction.cc
@@ -11,6 +11,8 @@ put(Help, "instructions",
 :(before "End Help Contents")
 cerr << "  instructions\n";
 
+//:: Check for 'syntax errors'; missing or unexpected operands.
+
 :(scenario check_missing_imm8_operand)
 % Hide_errors = true;
 == 0x1
diff --git a/subx/023check_operand_sizes.cc b/subx/023check_operand_sizes.cc
new file mode 100644
index 00000000..3a492b0c
--- /dev/null
+++ b/subx/023check_operand_sizes.cc
@@ -0,0 +1,109 @@
+//:: Check that the different operands of an instruction aren't too large for their bitfields.
+
+:(scenario check_bitfield_sizes)
+% Hide_errors = true;
+== 0x1
+01/add 4/mod
++error: '4/mod' too large to fit in bitfield mod
+
+:(before "End Globals")
+map<string, uint32_t> Operand_bound;
+:(before "End One-time Setup")
+put(Operand_bound, "subop", 1<<3);
+put(Operand_bound, "mod", 1<<2);
+put(Operand_bound, "rm32", 1<<3);
+put(Operand_bound, "base", 1<<3);
+put(Operand_bound, "index", 1<<3);
+put(Operand_bound, "scale", 1<<2);
+put(Operand_bound, "r32", 1<<3);
+put(Operand_bound, "disp8", 1<<8);
+put(Operand_bound, "disp16", 1<<16);
+// no bound needed for disp32
+put(Operand_bound, "imm8", 1<<8);
+// no bound needed for imm32
+
+:(before "End One-time Setup")
+Transform.push_back(check_operand_bounds);
+:(code)
+void check_operand_bounds(/*const*/ program& p) {
+  if (p.segments.empty()) return;
+  const segment& seg = p.segments.at(0);
+  for (int i = 0;  i < SIZE(seg.lines);  ++i) {
+    const line& inst = seg.lines.at(i);
+    for (int i = first_operand(inst);  i < SIZE(inst.words);  ++i)
+      check_operand_bounds(inst.words.at(i));
+    if (trace_contains_errors()) return;  // stop at the first mal-formed instruction
+  }
+}
+
+void check_operand_bounds(const word& w) {
+  for (map<string, uint32_t>::iterator p = Operand_bound.begin();  p != Operand_bound.end();  ++p)
+    if (has_metadata(w, p->first))
+      if (parse_int(w.data) >= p->second)
+        raise << "'" << w.original << "' too large to fit in bitfield " << p->first << '\n' << end();
+}
+
+int first_operand(const line& inst) {
+  if (inst.words.at(0).data == "0f") return 2;
+  if (inst.words.at(0).data == "f3") {
+    if (inst.words.at(1).data == "0f")
+      return 3;
+    else
+      return 2;
+  }
+  return 1;
+}
+
+uint32_t parse_int(const string& s) {
+  istringstream in(s);
+  uint32_t result = 0;
+  if (starts_with(s, "0x"))
+    in >> std::hex;
+  in >> result;
+  if (!in) {
+    raise << "not a number: " << s << '\n' << end();
+    return 0;
+  }
+  return result;
+}
+
+void check_metadata_present(const line& inst, const string& type, uint8_t op) {
+  if (!has_metadata(inst, type, op))
+    raise << "'" << to_string(inst) << "' (" << get(name, op) << "): missing " << type << " operand\n" << end();
+}
+
+bool has_metadata(const line& inst, const string& m, uint8_t op) {
+  bool result = false;
+  for (int i = 0;  i < SIZE(inst.words);  ++i) {
+    if (!has_metadata(inst.words.at(i), m)) continue;
+    if (result) {
+      raise << "'" << to_string(inst) << "' has conflicting " << m << " operands\n" << end();
+      return false;
+    }
+    result = true;
+  }
+  return result;
+}
+
+bool has_metadata(const word& w, const string& m) {
+  bool result = false;
+  bool metadata_found = false;
+  for (int i = 0;  i < SIZE(w.metadata);  ++i) {
+    const string& curr = w.metadata.at(i);
+    if (!contains_key(Operand_bound, curr)) continue;  // ignore unrecognized metadata
+    if (metadata_found) {
+      raise << "'" << w.original << "' has conflicting operand types; it should have only one\n" << end();
+      return false;
+    }
+    metadata_found = true;
+    result = (curr == m);
+  }
+  return result;
+}
+
+word metadata(const line& inst, const string& m) {
+  for (int i = 0;  i < SIZE(inst.words);  ++i)
+    if (has_metadata(inst.words.at(i), m))
+      return inst.words.at(i);
+  assert(false);
+}
diff --git a/subx/024transform_immediate.cc b/subx/024transform_immediate.cc
index 3784f9c0..0451a7c9 100644
--- a/subx/024transform_immediate.cc
+++ b/subx/024transform_immediate.cc
@@ -109,19 +109,6 @@ string to_string(const vector<word>& in) {
   return out.str();
 }
 
-uint32_t parse_int(const string& s) {
-  istringstream in(s);
-  uint32_t result = 0;
-  if (starts_with(s, "0x"))
-    in >> std::hex;
-  in >> result;
-  if (!in) {
-    raise << "not a number: " << s << '\n' << end();
-    return 0;
-  }
-  return result;
-}
-
 string serialize_hex(const int val) {
   ostringstream out;
   out << std::hex << val;