lib9p: protogen: pull cutil.py out of __init__.py

2 files changed, 148 insertions, 123 deletions

diff --git a/lib9p/protogen/__init__.py b/lib9p/protogen/__init__.py
index 21b5161..8a9a371 100644
--- a/lib9p/protogen/__init__.py
+++ b/lib9p/protogen/__init__.py
@@ -1,6 +1,5 @@
 # lib9p/protogen/__init__.py - Generate C marshalers/unmarshalers for
-#                              .9p files defining 9P protocol
-#                              variants.
+#                              .9p files defining 9P protocol variants
 #
 # Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
 # SPDX-License-Identifier: AGPL-3.0-or-later
@@ -13,6 +12,8 @@ import typing
 
 import idl
 
+from . import cutil
+
 # This strives to be "general-purpose" in that it just acts on the
 # *.9p inputs; but (unfortunately?) there are a few special-cases in
 # this script, marked with "SPECIAL".
@@ -25,16 +26,6 @@ __all__ = ["main"]
 
 idprefix = "lib9p_"
 
-u32max = (1 << 32) - 1
-u64max = (1 << 64) - 1
-
-
-def tab_ljust(s: str, width: int) -> str:
-    cur = len(s.expandtabs(tabsize=8))
-    if cur >= width:
-        return s
-    return s + " " * (width - cur)
-
 
 def add_prefix(p: str, s: str) -> str:
     if s.startswith("_"):
@@ -42,15 +33,6 @@ def add_prefix(p: str, s: str) -> str:
     return p + s
 
 
-def c_macro(full: str) -> str:
-    full = full.rstrip()
-    assert "\n" in full
-    lines = [l.rstrip() for l in full.split("\n")]
-    width = max(len(l.expandtabs(tabsize=8)) for l in lines[:-1])
-    lines = [tab_ljust(l, width) for l in lines]
-    return "  \\\n".join(lines).rstrip() + "\n"
-
-
 def c_ver_enum(ver: str) -> str:
     return f"{idprefix.upper()}VER_{ver.replace('.', '_')}"
 
@@ -105,47 +87,6 @@ def c_expr(expr: idl.Expr, lookup_sym: typing.Callable[[str], str]) -> str:
     return " ".join(ret)
 
 
-_ifdef_stack: list[str | None] = []
-
-
-def ifdef_push(n: int, _newval: str) -> str:
-    # Grow the stack as needed
-    while len(_ifdef_stack) < n:
-        _ifdef_stack.append(None)
-
-    # Set some variables
-    parentval: str | None = None
-    for x in _ifdef_stack[:-1]:
-        if x is not None:
-            parentval = x
-    oldval = _ifdef_stack[-1]
-    newval: str | None = _newval
-    if newval == parentval:
-        newval = None
-
-    # Put newval on the stack.
-    _ifdef_stack[-1] = newval
-
-    # Build output.
-    ret = ""
-    if newval != oldval:
-        if oldval is not None:
-            ret += f"#endif /* {oldval} */\n"
-        if newval is not None:
-            ret += f"#if {newval}\n"
-    return ret
-
-
-def ifdef_pop(n: int) -> str:
-    global _ifdef_stack
-    ret = ""
-    while len(_ifdef_stack) > n:
-        if _ifdef_stack[-1] is not None:
-            ret += f"#endif /* {_ifdef_stack[-1]} */\n"
-        _ifdef_stack = _ifdef_stack[:-1]
-    return ret
-
-
 # topo_sorted() ################################################################
 
 
@@ -378,8 +319,7 @@ def get_buffer_size(typ: idl.Type, version: str) -> BufferSize:
 
 
 def gen_h(versions: set[str], typs: list[idl.UserType]) -> str:
-    global _ifdef_stack
-    _ifdef_stack = []
+    cutil.ifdef_init()
 
     ret = f"""/* Generated by `{' '.join(sys.argv)}`.  DO NOT EDIT!  */
 
@@ -424,10 +364,10 @@ enum {idprefix}version {{
     verwidth = max(len(v) for v in fullversions)
     for ver in fullversions:
         if ver in versions:
-            ret += ifdef_push(1, c_ver_ifdef({ver}))
+            ret += cutil.ifdef_push(1, c_ver_ifdef({ver}))
         ret += f"\t{c_ver_enum(ver)},"
         ret += (" " * (verwidth - len(ver))) + ' /* "' + ver.split()[0] + '" */\n'
-    ret += ifdef_pop(0)
+    ret += cutil.ifdef_pop(0)
     ret += f"\t{c_ver_enum('NUM')},\n"
     ret += "};\n"
 
@@ -441,9 +381,9 @@ enum {idprefix}version {{
         if n not in id2typ:
             continue
         msg = id2typ[n]
-        ret += ifdef_push(1, c_ver_ifdef(msg.in_versions))
+        ret += cutil.ifdef_push(1, c_ver_ifdef(msg.in_versions))
         ret += f"\t{idprefix.upper()}TYP_{msg.typname:<{namewidth}} = {msg.msgid},\n"
-    ret += ifdef_pop(0)
+    ret += cutil.ifdef_pop(0)
     ret += "};\n"
 
     ret += """
@@ -469,21 +409,21 @@ enum {idprefix}version {{
 
     for typ in topo_sorted(typs):
         ret += "\n"
-        ret += ifdef_push(1, c_ver_ifdef(typ.in_versions))
+        ret += cutil.ifdef_push(1, c_ver_ifdef(typ.in_versions))
 
         def sum_size(typ: idl.UserType, version: str) -> str:
             sz = get_buffer_size(typ, version)
             assert (
                 sz.min_size <= sz.exp_size
                 and sz.exp_size <= sz.max_size
-                and sz.max_size < u64max
+                and sz.max_size < cutil.UINT64_MAX
             )
             ret = ""
             if sz.min_size == sz.max_size:
                 ret += f"size = {sz.min_size:,}"
             else:
                 ret += f"min_size = {sz.min_size:,} ; exp_size = {sz.exp_size:,} ; max_size = {sz.max_size:,}"
-            if sz.max_size > u32max:
+            if sz.max_size > cutil.UINT32_MAX:
                 ret += " (warning: >UINT32_MAX)"
             ret += f" ; max_iov = {sz.max_iov:,}{sz.max_iov_extra} ; max_copy = {sz.max_copy:,}{sz.max_copy_extra}"
             return ret
@@ -527,7 +467,7 @@ enum {idprefix}version {{
                     vers = bit.in_versions
                     if bit.cat == idl.BitCat.UNUSED:
                         vers = typ.in_versions
-                    ret += ifdef_push(2, c_ver_ifdef(vers))
+                    ret += cutil.ifdef_push(2, c_ver_ifdef(vers))
 
                     # It is important all of the `beg` strings have
                     # the same length.
@@ -536,10 +476,10 @@ enum {idprefix}version {{
                         case (
                             idl.BitCat.USED | idl.BitCat.RESERVED | idl.BitCat.SUBFIELD
                         ):
-                            if _ifdef_stack[-1]:
-                                beg = "#  define"
-                            else:
+                            if cutil.ifdef_leaf_is_noop():
                                 beg = "#define  "
+                            else:
+                                beg = "#  define"
                         case idl.BitCat.UNUSED:
                             beg = "/* unused"
                             end = " */"
@@ -555,18 +495,18 @@ enum {idprefix}version {{
                     ret += "\n"
 
                     for alias in aliases:
-                        ret += ifdef_push(2, c_ver_ifdef(alias.in_versions))
+                        ret += cutil.ifdef_push(2, c_ver_ifdef(alias.in_versions))
 
                         end = ""
-                        if _ifdef_stack[-1]:
-                            beg = "#  define"
-                        else:
+                        if cutil.ifdef_leaf_is_noop():
                             beg = "#define  "
+                        else:
+                            beg = "#  define"
 
                         c_name = bitname(alias)
                         c_val = alias.val
                         ret += f"{beg} {c_name:<{namewidth}}  (({c_typename(typ)})({c_val})){end}\n"
-                ret += ifdef_pop(1)
+                ret += cutil.ifdef_pop(1)
                 del bitname
             case idl.Struct():  # and idl.Message():
                 ret += c_typename(typ) + " {"
@@ -580,12 +520,12 @@ enum {idprefix}version {{
                 for member in typ.members:
                     if member.val:
                         continue
-                    ret += ifdef_push(2, c_ver_ifdef(member.in_versions))
+                    ret += cutil.ifdef_push(2, c_ver_ifdef(member.in_versions))
                     ret += f"\t{c_typename(member.typ, member):<{typewidth}}  {'*' if member.cnt else ' '}{member.membname};\n"
-                ret += ifdef_pop(1)
+                ret += cutil.ifdef_pop(1)
                 ret += "};\n"
         del typ
-    ret += ifdef_pop(0)
+    ret += cutil.ifdef_pop(0)
 
     ret += """
 /* containers *****************************************************************/
@@ -675,8 +615,7 @@ enum {idprefix}version {{
 
 
 def gen_c(versions: set[str], typs: list[idl.UserType]) -> str:
-    global _ifdef_stack
-    _ifdef_stack = []
+    cutil.ifdef_init()
 
     ret = f"""/* Generated by `{' '.join(sys.argv)}`.  DO NOT EDIT!  */
 
@@ -711,7 +650,7 @@ def gen_c(versions: set[str], typs: list[idl.UserType]) -> str:
         ret = f"const {tentry} _{idprefix}table_{grp}_{meth}[{c_ver_enum('NUM')}][{hex(len(range(*rng)))}] = {{\n"
         for ver in ["unknown", *sorted(versions)]:
             if ver != "unknown":
-                ret += ifdef_push(1, c_ver_ifdef({ver}))
+                ret += cutil.ifdef_push(1, c_ver_ifdef({ver}))
             ret += f"\t[{c_ver_enum(ver)}] = {{\n"
             for n in range(*rng):
                 xmsg: idl.Message | None = id2typ.get(n, None)
@@ -725,7 +664,7 @@ def gen_c(versions: set[str], typs: list[idl.UserType]) -> str:
                 if xmsg:
                     ret += f"\t\t_MSG_{meth.upper()}({xmsg.typname}),\n"
             ret += "\t},\n"
-        ret += ifdef_pop(0)
+        ret += cutil.ifdef_pop(0)
         ret += "};\n"
         return ret
 
@@ -752,9 +691,9 @@ const char *const _{idprefix}table_ver_name[{c_ver_enum('NUM')}] = {{
 """
     for ver in ["unknown", *sorted(versions)]:
         if ver in versions:
-            ret += ifdef_push(1, c_ver_ifdef({ver}))
+            ret += cutil.ifdef_push(1, c_ver_ifdef({ver}))
         ret += f'\t[{c_ver_enum(ver)}] = "{ver}",\n'
-    ret += ifdef_pop(0)
+    ret += cutil.ifdef_pop(0)
     ret += "};\n"
 
     ret += "\n"
@@ -769,11 +708,11 @@ const char *const _{idprefix}table_ver_name[{c_ver_enum('NUM')}] = {{
         if not isinstance(typ, idl.Bitfield):
             continue
         ret += "\n"
-        ret += ifdef_push(1, c_ver_ifdef(typ.in_versions))
+        ret += cutil.ifdef_push(1, c_ver_ifdef(typ.in_versions))
         ret += f"static const {c_typename(typ)} {typ.typname}_masks[{c_ver_enum('NUM')}] = {{\n"
         verwidth = max(len(ver) for ver in versions)
         for ver in sorted(versions):
-            ret += ifdef_push(2, c_ver_ifdef({ver}))
+            ret += cutil.ifdef_push(2, c_ver_ifdef({ver}))
             ret += (
                 f"\t[{c_ver_enum(ver)}]{' '*(verwidth-len(ver))} = 0b"
                 + "".join(
@@ -787,9 +726,9 @@ const char *const _{idprefix}table_ver_name[{c_ver_enum('NUM')}] = {{
                 )
                 + ",\n"
             )
-        ret += ifdef_pop(1)
+        ret += cutil.ifdef_pop(1)
         ret += "};\n"
-    ret += ifdef_pop(0)
+    ret += cutil.ifdef_pop(0)
 
     # validate_* ###############################################################
     ret += """
@@ -839,7 +778,7 @@ LM_ALWAYS_INLINE static bool validate_8(struct _validate_ctx *ctx) { return _val
         inline = "LM_FLATTEN" if isinstance(typ, idl.Message) else "LM_ALWAYS_INLINE"
         argfn = unused if (isinstance(typ, idl.Struct) and not typ.members) else used
         ret += "\n"
-        ret += ifdef_push(1, c_ver_ifdef(typ.in_versions))
+        ret += cutil.ifdef_push(1, c_ver_ifdef(typ.in_versions))
         ret += f"{inline} static bool validate_{typ.typname}(struct _validate_ctx *{argfn('ctx')}) {{\n"
 
         match typ:
@@ -865,9 +804,9 @@ LM_ALWAYS_INLINE static bool validate_8(struct _validate_ctx *ctx) { return _val
                 # Pass 1 - declare value variables
                 for member in typ.members:
                     if should_save_value(typ, member):
-                        ret += ifdef_push(2, c_ver_ifdef(member.in_versions))
+                        ret += cutil.ifdef_push(2, c_ver_ifdef(member.in_versions))
                         ret += f"\t{c_typename(member.typ)} {member.membname};\n"
-                ret += ifdef_pop(1)
+                ret += cutil.ifdef_pop(1)
 
                 # Pass 2 - declare offset variables
                 mark_offset: set[str] = set()
@@ -881,7 +820,7 @@ LM_ALWAYS_INLINE static bool validate_8(struct _validate_ctx *ctx) { return _val
                 # Pass 3 - main pass
                 ret += "\treturn false\n"
                 for member in typ.members:
-                    ret += ifdef_push(2, c_ver_ifdef(member.in_versions))
+                    ret += cutil.ifdef_push(2, c_ver_ifdef(member.in_versions))
                     ret += "\t    || "
                     if member.in_versions != typ.in_versions:
                         ret += "( " + c_ver_cond(member.in_versions) + " && "
@@ -925,20 +864,20 @@ LM_ALWAYS_INLINE static bool validate_8(struct _validate_ctx *ctx) { return _val
                     if member.max:
                         assert member.static_size
                         nbits = member.static_size * 8
-                        ret += ifdef_push(2, c_ver_ifdef(member.in_versions))
+                        ret += cutil.ifdef_push(2, c_ver_ifdef(member.in_versions))
                         ret += f"\t    || ({{ uint{nbits}_t max = {c_expr(member.max, lookup_sym)}; (((uint{nbits}_t){member.membname}) > max) &&\n"
                         ret += f'\t          lib9p_errorf(ctx->ctx, LINUX_EBADMSG, "{member.membname} value is too large (%"PRIu{nbits}" > %"PRIu{nbits}")", {member.membname}, max); }})\n'
                     if member.val:
                         assert member.static_size
                         nbits = member.static_size * 8
-                        ret += ifdef_push(2, c_ver_ifdef(member.in_versions))
+                        ret += cutil.ifdef_push(2, c_ver_ifdef(member.in_versions))
                         ret += f"\t    || ({{ uint{nbits}_t exp = {c_expr(member.val, lookup_sym)}; (((uint{nbits}_t){member.membname}) != exp) &&\n"
                         ret += f'\t          lib9p_errorf(ctx->ctx, LINUX_EBADMSG, "{member.membname} value is wrong (actual:%"PRIu{nbits}" != correct:%"PRIu{nbits}")", (uint{nbits}_t){member.membname}, exp); }})\n'
 
-                ret += ifdef_pop(1)
+                ret += cutil.ifdef_pop(1)
                 ret += "\t    ;\n"
         ret += "}\n"
-    ret += ifdef_pop(0)
+    ret += cutil.ifdef_pop(0)
 
     # unmarshal_* ##############################################################
     ret += """
@@ -968,7 +907,7 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
         inline = "LM_FLATTEN" if isinstance(typ, idl.Message) else "LM_ALWAYS_INLINE"
         argfn = unused if (isinstance(typ, idl.Struct) and not typ.members) else used
         ret += "\n"
-        ret += ifdef_push(1, c_ver_ifdef(typ.in_versions))
+        ret += cutil.ifdef_push(1, c_ver_ifdef(typ.in_versions))
         ret += f"{inline} static void unmarshal_{typ.typname}(struct _unmarshal_ctx *{argfn('ctx')}, {c_typename(typ)} *out) {{\n"
         match typ:
             case idl.Number():
@@ -979,7 +918,7 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
                 ret += "\tmemset(out, 0, sizeof(*out));\n"
 
                 for member in typ.members:
-                    ret += ifdef_push(2, c_ver_ifdef(member.in_versions))
+                    ret += cutil.ifdef_push(2, c_ver_ifdef(member.in_versions))
                     if member.val:
                         ret += f"\tctx->net_offset += {member.static_size};\n"
                         continue
@@ -1005,16 +944,16 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
                             ret += "\t}\n"
                     else:
                         ret += f"unmarshal_{member.typ.typname}(ctx, &out->{member.membname});\n"
-        ret += ifdef_pop(1)
+        ret += cutil.ifdef_pop(1)
         ret += "}\n"
-    ret += ifdef_pop(0)
+    ret += cutil.ifdef_pop(0)
 
     # marshal_* ################################################################
     ret += """
 /* marshal_* ******************************************************************/
 
 """
-    ret += c_macro(
+    ret += cutil.macro(
         "#define MARSHAL_BYTES_ZEROCOPY(ctx, data, len)\n"
         "\tif (ctx->net_iov[ctx->net_iov_cnt-1].iov_len)\n"
         "\t\tctx->net_iov_cnt++;\n"
@@ -1022,7 +961,7 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
         "\tctx->net_iov[ctx->net_iov_cnt-1].iov_len = len;\n"
         "\tctx->net_iov_cnt++;\n"
     )
-    ret += c_macro(
+    ret += cutil.macro(
         "#define MARSHAL_BYTES(ctx, data, len)\n"
         "\tif (!ctx->net_iov[ctx->net_iov_cnt-1].iov_base)\n"
         "\t\tctx->net_iov[ctx->net_iov_cnt-1].iov_base = &ctx->net_copied[ctx->net_copied_size];\n"
@@ -1030,7 +969,7 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
         "\tctx->net_copied_size += len;\n"
         "\tctx->net_iov[ctx->net_iov_cnt-1].iov_len += len;\n"
     )
-    ret += c_macro(
+    ret += cutil.macro(
         "#define MARSHAL_U8LE(ctx, val)\n"
         "\tif (!ctx->net_iov[ctx->net_iov_cnt-1].iov_base)\n"
         "\t\tctx->net_iov[ctx->net_iov_cnt-1].iov_base = &ctx->net_copied[ctx->net_copied_size];\n"
@@ -1038,7 +977,7 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
         "\tctx->net_copied_size += 1;\n"
         "\tctx->net_iov[ctx->net_iov_cnt-1].iov_len += 1;\n"
     )
-    ret += c_macro(
+    ret += cutil.macro(
         "#define MARSHAL_U16LE(ctx, val)\n"
         "\tif (!ctx->net_iov[ctx->net_iov_cnt-1].iov_base)\n"
         "\t\tctx->net_iov[ctx->net_iov_cnt-1].iov_base = &ctx->net_copied[ctx->net_copied_size];\n"
@@ -1046,7 +985,7 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
         "\tctx->net_copied_size += 2;\n"
         "\tctx->net_iov[ctx->net_iov_cnt-1].iov_len += 2;\n"
     )
-    ret += c_macro(
+    ret += cutil.macro(
         "#define MARSHAL_U32LE(ctx, val)\n"
         "\tif (!ctx->net_iov[ctx->net_iov_cnt-1].iov_base)\n"
         "\t\tctx->net_iov[ctx->net_iov_cnt-1].iov_base = &ctx->net_copied[ctx->net_copied_size];\n"
@@ -1054,7 +993,7 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
         "\tctx->net_copied_size += 4;\n"
         "\tctx->net_iov[ctx->net_iov_cnt-1].iov_len += 4;\n"
     )
-    ret += c_macro(
+    ret += cutil.macro(
         "#define MARSHAL_U64LE(ctx, val)\n"
         "\tif (!ctx->net_iov[ctx->net_iov_cnt-1].iov_base)\n"
         "\t\tctx->net_iov[ctx->net_iov_cnt-1].iov_base = &ctx->net_copied[ctx->net_copied_size];\n"
@@ -1108,11 +1047,11 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
                 )
                 multiline += f"{'\t'*indent_depth}}}\n"
             for vers, sub in self.cond.items():
-                multiline += ifdef_push(indent_depth + 1, c_ver_ifdef(vers))
+                multiline += cutil.ifdef_push(indent_depth + 1, c_ver_ifdef(vers))
                 multiline += f"{'\t'*indent_depth}if {c_ver_cond(vers)} {{\n"
                 multiline += sub.gen_c("", dstvar, root, indent_depth + 1, loop_depth)
                 multiline += f"{'\t'*indent_depth}}}\n"
-                multiline += ifdef_pop(indent_depth)
+                multiline += cutil.ifdef_pop(indent_depth)
             if dsttyp:
                 if not oneline:
                     oneline.append("0")
@@ -1204,13 +1143,13 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
             continue
         assert isinstance(typ, idl.Struct)
         ret += "\n"
-        ret += ifdef_push(1, c_ver_ifdef(typ.in_versions))
+        ret += cutil.ifdef_push(1, c_ver_ifdef(typ.in_versions))
         ret += f"static bool marshal_{typ.typname}(struct _marshal_ctx *ctx, {c_typename(typ)} *val) {{\n"
 
         # Pass 1 - check size
         max_size = max(typ.max_size(v) for v in typ.in_versions)
 
-        if max_size > u32max:  # SPECIAL (9P2000.e)
+        if max_size > cutil.UINT32_MAX:  # SPECIAL (9P2000.e)
             ret += get_offset_expr(typ, go_to_end).gen_c(
                 "uint64_t", "needed_size", "val->", 1, 0
             )
@@ -1247,7 +1186,7 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
                     ret += f"{'\t'*(len(stack)-1)}}}\n"
                     if stack[-1][1]:
                         ifdef_depth -= 1
-                        ret += ifdef_pop(ifdef_depth)
+                        ret += cutil.ifdef_pop(ifdef_depth)
                     stack = stack[:-1]
 
             loopdepth = sum(1 for elem in path.elems if elem.cnt)
@@ -1270,7 +1209,7 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
                     if name == "end":
                         if not path.elems:
                             nonlocal max_size
-                            if max_size > u32max:
+                            if max_size > cutil.UINT32_MAX:
                                 ret += f"{'\t'*len(stack)}uint32_t {name_prefix}end = (uint32_t)needed_size;\n"
                             else:
                                 ret += f"{'\t'*len(stack)}uint32_t {name_prefix}end = needed_size;\n"
@@ -1295,7 +1234,9 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
                 child = path.elems[-1]
                 parent = path.elems[-2].typ if len(path.elems) > 1 else path.root
                 if child.in_versions < parent.in_versions:
-                    ret += ifdef_push(ifdef_depth + 1, c_ver_ifdef(child.in_versions))
+                    ret += cutil.ifdef_push(
+                        ifdef_depth + 1, c_ver_ifdef(child.in_versions)
+                    )
                     ifdef_depth += 1
                     ret += f"{'\t'*len(stack)}if ({c_ver_cond(child.in_versions)}) {{\n"
                     stack.append((path, True))
@@ -1338,7 +1279,7 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
 
         ret += "\treturn false;\n"
         ret += "}\n"
-    ret += ifdef_pop(0)
+    ret += cutil.ifdef_pop(0)
 
     # function tables ##########################################################
     ret += """
@@ -1350,20 +1291,20 @@ LM_ALWAYS_INLINE static void unmarshal_8(struct _unmarshal_ctx *ctx, uint64_t *o
     rerror = next(typ for typ in typs if typ.typname == "Rerror")
     ret += f"\t[{c_ver_enum('unknown')}] = {rerror.min_size('9P2000')},\n"  # SPECIAL (initialization)
     for ver in sorted(versions):
-        ret += ifdef_push(1, c_ver_ifdef({ver}))
+        ret += cutil.ifdef_push(1, c_ver_ifdef({ver}))
         ret += f"\t[{c_ver_enum(ver)}] = {rerror.min_size(ver)},\n"
-    ret += ifdef_pop(0)
+    ret += cutil.ifdef_pop(0)
     ret += "};\n"
 
     ret += "\n"
-    ret += c_macro(
+    ret += cutil.macro(
         f"#define _MSG_RECV(typ) [{idprefix.upper()}TYP_##typ/2] = {{\n"
         f"\t\t.basesize  = sizeof(struct {idprefix}msg_##typ),\n"
         f"\t\t.validate  = validate_##typ,\n"
         f"\t\t.unmarshal = (_unmarshal_fn_t)unmarshal_##typ,\n"
         f"\t}}\n"
     )
-    ret += c_macro(
+    ret += cutil.macro(
         f"#define _MSG_SEND(typ) [{idprefix.upper()}TYP_##typ/2] = {{\n"
         f"\t\t.marshal   = (_marshal_fn_t)marshal_##typ,\n"
         f"\t}}\n"
diff --git a/lib9p/protogen/cutil.py b/lib9p/protogen/cutil.py
new file mode 100644
index 0000000..a78cd17
--- /dev/null
+++ b/lib9p/protogen/cutil.py
@@ -0,0 +1,84 @@
+# lib9p/protogen/cutil.py - Utilities for generating C code
+#
+# Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+# pylint: disable=unused-variable
+__all__ = [
+    "UINT32_MAX",
+    "UINT64_MAX",
+    "macro",
+    "ifdef_init",
+    "ifdef_push",
+    "ifdef_pop",
+    "ifdef_leaf_is_noop",
+]
+
+UINT32_MAX = (1 << 32) - 1
+UINT64_MAX = (1 << 64) - 1
+
+
+def tab_ljust(s: str, width: int) -> str:
+    cur = len(s.expandtabs(tabsize=8))
+    if cur >= width:
+        return s
+    return s + " " * (width - cur)
+
+
+def macro(full: str) -> str:
+    full = full.rstrip()
+    assert "\n" in full
+    lines = [l.rstrip() for l in full.split("\n")]
+    width = max(len(l.expandtabs(tabsize=8)) for l in lines[:-1])
+    lines = [tab_ljust(l, width) for l in lines]
+    return "  \\\n".join(lines).rstrip() + "\n"
+
+
+_ifdef_stack: list[str | None] = []
+
+
+def ifdef_init() -> None:
+    global _ifdef_stack
+    _ifdef_stack = []
+
+
+def ifdef_push(n: int, _newval: str) -> str:
+    # Grow the stack as needed
+    while len(_ifdef_stack) < n:
+        _ifdef_stack.append(None)
+
+    # Set some variables
+    parentval: str | None = None
+    for x in _ifdef_stack[:-1]:
+        if x is not None:
+            parentval = x
+    oldval = _ifdef_stack[-1]
+    newval: str | None = _newval
+    if newval == parentval:
+        newval = None
+
+    # Put newval on the stack.
+    _ifdef_stack[-1] = newval
+
+    # Build output.
+    ret = ""
+    if newval != oldval:
+        if oldval is not None:
+            ret += f"#endif /* {oldval} */\n"
+        if newval is not None:
+            ret += f"#if {newval}\n"
+    return ret
+
+
+def ifdef_pop(n: int) -> str:
+    global _ifdef_stack
+    ret = ""
+    while len(_ifdef_stack) > n:
+        if _ifdef_stack[-1] is not None:
+            ret += f"#endif /* {_ifdef_stack[-1]} */\n"
+        _ifdef_stack = _ifdef_stack[:-1]
+    return ret
+
+
+def ifdef_leaf_is_noop() -> bool:
+    return not _ifdef_stack[-1]