diff --git a/upb/decode.int.h b/upb/decode.int.h
new file mode 100644
index 0000000000..15194029f5
--- /dev/null
+++ b/upb/decode.int.h
@@ -0,0 +1,48 @@
+
+#ifndef UPB_DECODE_INT_H_
+#define UPB_DECODE_INT_H_
+
+#include "upb/upb.int.h"
+
+/* Must be last. */
+#include "upb/port_def.inc"
+
+typedef struct upb_decstate {
+  const char *limit;       /* End of delimited region or end of buffer. */
+  const char *fastlimit;   /* End of delimited region or end of buffer. */
+  const char *fastend;
+  upb_arena arena;
+  int depth;
+  uint32_t end_group; /* Set to field number of END_GROUP tag, if any. */
+  jmp_buf err;
+} upb_decstate;
+
+const char *fastdecode_dispatch(upb_decstate *d, const char *ptr, upb_msg *msg,
+                                const upb_msglayout *table, uint64_t hasbits);
+const char *fastdecode_err(upb_decstate *d);
+
+
+UPB_INLINE bool decode_arenahas(upb_decstate *d, size_t bytes) {
+  return (size_t)(d->arena.head.end - d->arena.head.ptr) >= bytes;
+}
+
+UPB_INLINE
+upb_msg *decode_newmsg_ceil(upb_decstate *d, const upb_msglayout *l,
+                            int msg_ceil_bytes) {
+  size_t size = l->size + sizeof(upb_msg_internal);
+  char *msg_data;
+  if (UPB_LIKELY(msg_ceil_bytes > 0 && decode_arenahas(d, msg_ceil_bytes))) {
+    UPB_ASSERT(size <= (size_t)msg_ceil_bytes);
+    msg_data = d->arena.head.ptr;
+    memset(msg_data, 0, msg_ceil_bytes);
+    d->arena.head.ptr += size;
+  } else {
+    msg_data = (char*)upb_arena_malloc(&d->arena, size);
+    memset(msg_data, 0, size);
+  }
+  return msg_data + sizeof(upb_msg_internal);
+}
+
+#include "upb/port_undef.inc"
+
+#endif  /* UPB_DECODE_INT_H_ */
diff --git a/upb/decode_fast.h b/upb/decode_fast.h
new file mode 100644
index 0000000000..47ca1bc4ba
--- /dev/null
+++ b/upb/decode_fast.h
@@ -0,0 +1,68 @@
+
+#ifndef UPB_DECODE_FAST_H_
+#define UPB_DECODE_FAST_H_
+
+#include "upb/msg.h"
+
+struct upb_decstate;
+
+const char *fastdecode_generic(struct upb_decstate *d, const char *ptr,
+                               upb_msg *msg, const upb_msglayout *table,
+                               uint64_t hasbits, uint64_t data);
+
+#define UPB_PARSE_PARAMS                                 \
+  struct upb_decstate *d, const char *ptr, upb_msg *msg, \
+      const upb_msglayout *table, uint64_t hasbits, uint64_t data
+
+#define F(card, type, valbytes, tagbytes) \
+  const char *upb_p##card##type##valbytes##_##tagbytes##bt(UPB_PARSE_PARAMS);
+
+#define TYPES(card, tagbytes) \
+  F(card, b, 1, tagbytes)     \
+  F(card, v, 4, tagbytes)     \
+  F(card, v, 8, tagbytes)     \
+  F(card, z, 4, tagbytes)     \
+  F(card, z, 8, tagbytes)
+
+#define TAGBYTES(card) \
+  TYPES(card, 1)       \
+  TYPES(card, 2)
+
+TAGBYTES(s)
+TAGBYTES(o)
+/* TAGBYTES(r) */
+
+const char *upb_pss_1bt(UPB_PARSE_PARAMS);
+const char *upb_pss_2bt(UPB_PARSE_PARAMS);
+const char *upb_pos_1bt(UPB_PARSE_PARAMS);
+const char *upb_pos_2bt(UPB_PARSE_PARAMS);
+
+#undef F
+#undef TYPES
+#undef TAGBYTES
+
+#define F(card, tagbytes, size_ceil, ceil_arg) \
+  const char *upb_p##card##m_##tagbytes##bt_max##size_ceil##b(UPB_PARSE_PARAMS);
+
+#define SIZES(card, tagbytes) \
+  F(card, tagbytes, 64, 64) \
+  F(card, tagbytes, 128, 128) \
+  F(card, tagbytes, 192, 192) \
+  F(card, tagbytes, 256, 256) \
+  F(card, tagbytes, max, -1)
+
+#define TAGBYTES(card) \
+  SIZES(card, 1) \
+  SIZES(card, 2)
+
+TAGBYTES(s)
+TAGBYTES(o)
+TAGBYTES(r)
+
+#undef TAGBYTES
+#undef SIZES
+#undef F
+
+#undef UPB_PARSE_PARAMS
+
+#endif  /* UPB_DECODE_FAST_H_ */