3 files changed, 121 insertions, 1 deletions
diff --git a/src/interp/ops.c b/src/interp/ops.c
index 4366a49..7c0d911 100644
--- a/src/interp/ops.c
+++ b/src/interp/ops.c
@@ -41,7 +41,7 @@ static void (*const ops[])(struct nw_interp *) =
     NULL,
     NULL,
     nwp_op_drop, /* OP_DROP */
-    NULL, /* OP_SELECT */
+    nwp_op_select, /* OP_SELECT */
     NULL,
     NULL,
     NULL,
diff --git a/src/op/CMakeLists.txt b/src/op/CMakeLists.txt
index 7cc6ff8..90ce763 100644
--- a/src/op/CMakeLists.txt
+++ b/src/op/CMakeLists.txt
@@ -49,6 +49,7 @@ target_sources(${PROJECT_NAME} PRIVATE
     loop.c
     nop.c
     return.c
+    select.c
     set_global.c
     set_local.c
     tee_local.c
diff --git a/src/op/select.c b/src/op/select.c
new file mode 100644
index 0000000..7705af9
--- /dev/null
+++ b/src/op/select.c
@@ -0,0 +1,119 @@
+/*
+ * 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 <nw/interp.h>
+#include <nw/io.h>
+#include <nw/log.h>
+#include <nw/opcodes.h>
+#include <nw/ops.h>
+#include <nw/stack.h>
+#include <nw/types.h>
+
+static enum nw_state push(struct nw_interp *const i)
+{
+    struct nw_i_sm_select *const s = &i->sm.select;
+    const enum nw_state n = nwp_stack_push(i, &s->io);
+
+    if (n)
+        return n;
+
+    nwp_interp_resume(i);
+    return NW_AGAIN;
+}
+
+static enum nw_state pop_left(struct nw_interp *const i)
+{
+    struct nw_i_sm_select *const s = &i->sm.select;
+    const enum nw_state n = nwp_stack_pop(i, &s->io);
+    struct nw_sm_io io = {0};
+
+    if (n)
+        return n;
+
+    io.buf = s->condition ? &s->left : &s->right;
+    io.n = s->sz;
+    s->io = io;
+    i->next = push;
+    return NW_AGAIN;
+}
+
+static enum nw_state pop_right(struct nw_interp *const i)
+{
+    struct nw_i_sm_select *const s = &i->sm.select;
+    const enum nw_state n = nwp_stack_pop(i, &s->io);
+
+    if (n)
+        return n;
+    else
+    {
+        struct nw_sm_io io = {0};
+
+        io.buf = &s->left;
+        io.n = s->sz;
+        s->io = io;
+    }
+
+    i->next = pop_left;
+    return NW_AGAIN;
+}
+
+static enum nw_state pop_condition(struct nw_interp *const i)
+{
+    struct nw_i_sm_select *const s = &i->sm.select;
+    const enum nw_state n = nwp_stack_pop(i, &s->io);
+
+    if (n)
+        return n;
+    else
+    {
+        struct nw_sm_io io = {0};
+
+        io.buf = &s->right;
+        io.n = s->sz;
+        s->io = io;
+    }
+
+    i->next = pop_right;
+    return NW_AGAIN;
+}
+
+static enum nw_state check(struct nw_interp *const i)
+{
+    struct nw_i_sm_select *const s = &i->sm.select;
+
+    if (nwp_type_sz(i->push_type, &s->sz))
+    {
+        static const char *const exc = "invalid type";
+
+        i->exception = exc;
+#ifdef NW_LOG
+        nwp_log("%s: %#x\n", exc, (unsigned)i->push_type);
+#endif
+        return NW_FATAL;
+    }
+    else
+    {
+        struct nw_sm_io io = {0};
+
+        io.buf = &s->condition;
+        io.n = sizeof s->condition;
+        s->io = io;
+    }
+
+    i->next = pop_condition;
+    return NW_AGAIN;
+}
+
+void nwp_op_select(struct nw_interp *const i)
+{
+    const struct nw_i_sm_select s = {0};
+
+    i->sm.select = s;
+    i->next = check;
+}