7 files changed, 92 insertions, 11 deletions
diff --git a/src/interp/ops.c b/src/interp/ops.c
index de69126..2bfdff0 100644
--- a/src/interp/ops.c
+++ b/src/interp/ops.c
@@ -18,8 +18,8 @@ static void (*const ops[])(struct nw_interp *) =
     nwp_op_nop, /* OP_NOP */
     nwp_op_block, /* OP_BLOCK */
     nwp_op_loop, /* OP_LOOP */
-    NULL, /* OP_IF */
-    NULL, /* OP_ELSE */
+    nwp_op_if, /* OP_IF */
+    nwp_op_else, /* OP_ELSE */
     NULL,
     NULL,
     NULL,
diff --git a/src/op/CMakeLists.txt b/src/op/CMakeLists.txt
index 4b4a531..bea3555 100644
--- a/src/op/CMakeLists.txt
+++ b/src/op/CMakeLists.txt
@@ -12,6 +12,7 @@ target_sources(${PROJECT_NAME} PRIVATE
     call.c
     call_indirect.c
     drop.c
+    else.c
     end.c
     get_local.c
     get_global.c
@@ -35,6 +36,7 @@ target_sources(${PROJECT_NAME} PRIVATE
     i32_sub.c
     i64_const.c
     i64_store.c
+    if.c
     loop.c
     nop.c
     return.c
diff --git a/src/op/block.c b/src/op/block.c
index e35a722..78651da 100644
--- a/src/op/block.c
+++ b/src/op/block.c
@@ -8,10 +8,17 @@
  */
 
 #include <nanowasm/nw.h>
+#include <nw/interp.h>
 #include <nw/ops.h>
 #include <nw/routines.h>
 
+static enum nw_state resume(struct nw_interp *const i)
+{
+    nwp_interp_resume(i);
+    return NW_AGAIN;
+}
+
 void nwp_op_block(struct nw_interp *const i)
 {
-    nwp_start_block(i);
+    nwp_start_block(i, &i->sm.start_block, resume);
 }
diff --git a/src/op/else.c b/src/op/else.c
new file mode 100644
index 0000000..2c1c6b1
--- /dev/null
+++ b/src/op/else.c
@@ -0,0 +1,18 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nanowasm/nw.h>
+#include <nw/interp.h>
+#include <nw/ops.h>
+#include <nw/routines.h>
+
+void nwp_op_else(struct nw_interp *const i)
+{
+    nwp_break(i, 0);
+}
diff --git a/src/op/if.c b/src/op/if.c
new file mode 100644
index 0000000..2ef9565
--- /dev/null
+++ b/src/op/if.c
@@ -0,0 +1,43 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nanowasm/nw.h>
+#include <nw/interp.h>
+#include <nw/io.h>
+#include <nw/ops.h>
+#include <nw/routines.h>
+#include <nw/stack.h>
+#include <nw/types.h>
+
+static enum nw_state pop(struct nw_interp *const i)
+{
+    struct nw_i_sm_if *const pif = &i->sm.sm_if;
+    const enum nw_state n = nwp_stack_pop(i, &pif->io);
+
+    if (n)
+        return n;
+    else if (pif->condition)
+        nwp_interp_resume(i);
+    else
+        nwp_break(i, 0);
+
+    return NW_AGAIN;
+}
+
+void nwp_op_if(struct nw_interp *const i)
+{
+    static const struct nw_i_sm_if sm_if;
+    struct nw_i_sm_if *const pif = &i->sm.sm_if;
+    struct nw_sm_io *const io = &pif->io;
+
+    *pif = sm_if;
+    io->buf = &pif->condition;
+    io->n = sizeof pif->condition;
+    nwp_start_block(i, &pif->sb, pop);
+}
diff --git a/src/op/loop.c b/src/op/loop.c
index e129610..cb3137b 100644
--- a/src/op/loop.c
+++ b/src/op/loop.c
@@ -8,9 +8,17 @@
  */
 
 #include <nanowasm/nw.h>
+#include <nw/interp.h>
+#include <nw/ops.h>
 #include <nw/routines.h>
 
+static enum nw_state resume(struct nw_interp *const i)
+{
+    nwp_interp_resume(i);
+    return NW_AGAIN;
+}
+
 void nwp_op_loop(struct nw_interp *const i)
 {
-    nwp_start_block(i);
+    nwp_start_block(i, &i->sm.start_block, resume);
 }
diff --git a/src/routines/start_block.c b/src/routines/start_block.c
index 83be44c..fb0b420 100644
--- a/src/routines/start_block.c
+++ b/src/routines/start_block.c
@@ -17,7 +17,7 @@
 static enum nw_state get_block_type(struct nw_interp *const i)
 {
     nw_varint7 type;
-    struct nw_i_sm_sb *const sb = &i->sm.start_block;
+    struct nw_i_sm_sb *const sb = i->state;
     const struct nw_io_cfg *const cfg = &i->cfg.io;
     const enum nw_state n = nwp_varint7(cfg, &sb->leb128, &type, cfg->user);
     enum nw_type block_type;
@@ -26,24 +26,27 @@ static enum nw_state get_block_type(struct nw_interp *const i)
         return n;
     else if (type != 0x40 && nwp_get_type(type, &block_type))
     {
-        static const char *const exc = "invalid block_type";
+        static const char *const exc = "invalid block type";
 
         i->exception = exc;
-#ifdef NW_LOG
-        nwp_log("%s: %#hhx\n", exc, (unsigned char)type);
+#ifdef ENABLE_LOG
+        nwp_log("%s: %#x\n", exc, (unsigned)type);
 #endif
         return NW_FATAL;
     }
 
     i->fr.block_i++;
-    nwp_interp_resume(i);
+    i->next = sb->next;
     return NW_AGAIN;
 }
 
-void nwp_start_block(struct nw_interp *const i)
+void nwp_start_block(struct nw_interp *const i, struct nw_i_sm_sb *const psb,
+    enum nw_state (*const next)(struct nw_interp *))
 {
     const struct nw_i_sm_sb sb = {0};
 
-    i->sm.start_block = sb;
+    *psb = sb;
+    psb->next = next;
+    i->state = psb;
     i->next = get_block_type;
 }