diff --git a/sm3/sm3block_ppc64x.s b/sm3/sm3block_ppc64x.s
index 3397dba..ebe19e2 100644
--- a/sm3/sm3block_ppc64x.s
+++ b/sm3/sm3block_ppc64x.s
@@ -136,10 +136,7 @@ GLOBL ·flip_mask(SB), RODATA, $16
 	P0(y2, y0, d)
 
 // r = s <<< n
-// Due to VSPLTISW's limitation, the n MUST be [0, 15],
-// If n > 15, we have to call it multiple times.
-// VSPLTISW takes a 5-bit immediate value as an operand.
-// I also did NOT find one vector instruction to use immediate value for ROTL.
+// Due to VSPLTISW's limitation, the n MUST be [0, 31]
 #define PROLD(s, r, n) \
 	VSPLTISW $n, XFER \
 	VRLW	s, XFER, r
diff --git a/sm3/sm3blocks_ppc64x.s b/sm3/sm3blocks_ppc64x.s
index 6a11c49..b9a549d 100644
--- a/sm3/sm3blocks_ppc64x.s
+++ b/sm3/sm3blocks_ppc64x.s
@@ -66,10 +66,7 @@ GLOBL ·mask(SB), RODATA, $80
 #endif // defined(GOARCH_ppc64le)
 
 // r = s <<< n
-// Due to VSPLTISW's limitation, the n MUST be [0, 15],
-// If n > 15, we have to call it multiple times.
-// VSPLTISW takes a 5-bit immediate value as an operand.
-// I also did NOT find one vector instruction to use immediate value for ROTL.
+// Due to VSPLTISW's limitation, the n MUST be [0, 31]
 #define PROLD(s, r, n) \
 	VSPLTISW $n, TMP5 \
 	VRLW	s, TMP5, r
diff --git a/sm4/gcm_ppc64x_test.go b/sm4/gcm_ppc64x_test.go
new file mode 100644
index 0000000..b9999fb
--- /dev/null
+++ b/sm4/gcm_ppc64x_test.go
@@ -0,0 +1,45 @@
+// Copyright 2024 Sun Yimin. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+//go:build (ppc64 || ppc64le) && !purego
+
+package sm4
+
+import (
+	"encoding/binary"
+	"fmt"
+	"runtime"
+	"testing"
+)
+
+func TestCmul(t *testing.T) {
+	key := make([]byte, 16)
+	c1 := &sm4CipherAsm{sm4Cipher{}, 4, 4 * BlockSize}
+	expandKeyAsm(&key[0], &ck[0], &c1.enc[0], &c1.dec[0], INST_AES)
+	hle := make([]byte, gcmBlockSize)
+	c1.Encrypt(hle, hle)
+	if fmt.Sprintf("%x", hle) != "9f1f7bff6f5511384d9430531e538fd3" {
+		t.Errorf("1 got %x", hle)
+	}
+	var h1, h2 uint64
+	// Reverse the bytes in each 8 byte chunk
+	// Load little endian, store big endian
+	if runtime.GOARCH == "ppc64le" {
+		h1 = binary.LittleEndian.Uint64(hle[:8])
+		h2 = binary.LittleEndian.Uint64(hle[8:])
+	} else {
+		h1 = binary.BigEndian.Uint64(hle[:8])
+		h2 = binary.BigEndian.Uint64(hle[8:])
+	}
+	binary.BigEndian.PutUint64(hle[:8], h1)
+	binary.BigEndian.PutUint64(hle[8:], h2)
+
+	if fmt.Sprintf("%x", hle) != "3811556fff7b1f9fd38f531e0530944d" {
+		t.Errorf("2 got %x", hle)
+	}
+	aead, _ := c1.NewGCM(12, 16)
+	for i := 0; i < 256; i += 16 {
+		fmt.Printf("%x\n", aead.(*gcmAsm).productTable[i:i+16])
+	}
+}