Add a method to sign-extend a Int128, along with unit tests.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 include/qemu/int128.h    | 10 ++++++++++
 tests/unit/test-int128.c | 22 ++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/qemu/int128.h b/include/qemu/int128.h
index 7b3b071c512..c2d6c183393 100644
--- a/include/qemu/int128.h
+++ b/include/qemu/int128.h
@@ -62,6 +62,11 @@ static inline Int128 int128_exts64(int64_t a)
     return a;
 }
 
+static inline Int128 int128_signextend(Int128 a)
+{
+    return int128_gethi(a) ? a : int128_exts64(int128_getlo(a));
+}
+
 static inline Int128 int128_not(Int128 a)
 {
     return ~a;
@@ -295,6 +300,11 @@ static inline Int128 int128_exts64(int64_t a)
     return int128_make128(a, (a < 0) ? -1 : 0);
 }
 
+static inline Int128 int128_signextend(Int128 a)
+{
+    return a.hi ? a : int128_exts64(a.lo);
+}
+
 static inline Int128 int128_not(Int128 a)
 {
     return int128_make128(~a.lo, ~a.hi);
diff --git a/tests/unit/test-int128.c b/tests/unit/test-int128.c
index 25db2455e80..526abd02e03 100644
--- a/tests/unit/test-int128.c
+++ b/tests/unit/test-int128.c
@@ -255,6 +255,27 @@ static void test_urshift(void)
                      0x8000000000000000ULL);
 }
 
+static void __attribute__((__noinline__)) ATTRIBUTE_NOCLONE
+test_signextend_one(uint64_t ah, uint64_t al, uint64_t rh, uint64_t rl)
+{
+    Int128 r = int128_make128(rl, rh);
+    Int128 s = int128_signextend(int128_make128(al, ah));
+    g_assert_cmphex(int128_getlo(r), ==, int128_getlo(s));
+    g_assert_cmphex(int128_gethi(r), ==, int128_gethi(s));
+}
+
+static void test_signextend(void)
+{
+    test_signextend_one(0x0000000000000000ULL, 0x0000000000000001ULL,
+                        0x0000000000000000ULL, 0x0000000000000001ULL);
+    test_signextend_one(0x0000000000000000ULL, 0x7FFFFFFFFFFFFFFEULL,
+                        0x0000000000000000ULL, 0x7FFFFFFFFFFFFFFEULL);
+    test_signextend_one(0x0000000000000000ULL, 0x8000000000000001ULL,
+                        0xFFFFFFFFFFFFFFFFULL, 0x8000000000000001ULL);
+    test_signextend_one(0xFFFFFFFFFFFFFFFFULL, 0xFFFFFFFFFFFFFFFEULL,
+                        0xFFFFFFFFFFFFFFFFULL, 0xFFFFFFFFFFFFFFFEULL);
+}
+
 int main(int argc, char **argv)
 {
     g_test_init(&argc, &argv, NULL);
@@ -269,5 +290,6 @@ int main(int argc, char **argv)
     g_test_add_func("/int128/int128_gt", test_gt);
     g_test_add_func("/int128/int128_rshift", test_rshift);
     g_test_add_func("/int128/int128_urshift", test_urshift);
+    g_test_add_func("/int128/int128_signextend", test_signextend);
     return g_test_run();
 }
-- 
2.52.0

On 2/4/26 09:00, Philippe Mathieu-Daudé wrote:
> Add a method to sign-extend a Int128, along with unit tests.

What in the world does this mean?

I can't imagine a real use for this:

> +static inline Int128 int128_signextend(Int128 a)
> +{
> +    return a.hi ? a : int128_exts64(a.lo);
> +}

r~

On 4/2/26 02:47, Richard Henderson wrote:
> On 2/4/26 09:00, Philippe Mathieu-Daudé wrote:
>> Add a method to sign-extend a Int128, along with unit tests.
> 
> What in the world does this mean?
> 
> I can't imagine a real use for this:
> 
>> +static inline Int128 int128_signextend(Int128 a)
>> +{
>> +    return a.hi ? a : int128_exts64(a.lo);
>> +}

Should we ignore MO_SIGN in do_ld16_mmu() in the
next patch then?

On 2/5/26 04:35, Philippe Mathieu-Daudé wrote:
> On 4/2/26 02:47, Richard Henderson wrote:
>> On 2/4/26 09:00, Philippe Mathieu-Daudé wrote:
>>> Add a method to sign-extend a Int128, along with unit tests.
>>
>> What in the world does this mean?
>>
>> I can't imagine a real use for this:
>>
>>> +static inline Int128 int128_signextend(Int128 a)
>>> +{
>>> +    return a.hi ? a : int128_exts64(a.lo);
>>> +}
> 
> Should we ignore MO_SIGN in do_ld16_mmu() in the
> next patch then?

Well, since the next patch is broken... yes.

r~