internal/sm2ec: loong64 p256Sub

internal/sm2ec/p256_asm_loong64.s

@@ -1287,7 +1287,69 @@ TEXT ·p256Select(SB),NOSPLIT,$0
 TEXT ·p256SelectAffine(SB),NOSPLIT,$0
 	RET
 
+/* ---------------------------------------*/
+// func p256Mul(res, in1, in2 *p256Element)
+TEXT ·p256Mul(SB),NOSPLIT,$0
+	MOVV res+0(FP), res_ptr
+	MOVV in1+8(FP), x_ptr
+	MOVV in2+16(FP), y_ptr
+	MOVV (8*0)(x_ptr), y0
+	MOVV (8*1)(x_ptr), y1
+	MOVV (8*2)(x_ptr), y2
+	MOVV (8*3)(x_ptr), y3
+
+	MOVV (8*0)(y_ptr), x0
+	MOVV (8*1)(y_ptr), x1
+	MOVV (8*2)(y_ptr), x2
+	MOVV (8*3)(y_ptr), x3
+
+	CALL sm2P256MulInternal<>(SB)
+
+	MOVV x0, (8*0)(res_ptr)
+	MOVV x1, (8*1)(res_ptr)
+	MOVV x2, (8*2)(res_ptr)
+	MOVV x3, (8*3)(res_ptr)
+	RET
+
 /* ---------------------------------------*/
 // (x3, x2, x1, x0) = (y3, y2, y1, y0) - (x3, x2, x1, x0)	
 TEXT sm2P256Subinternal<>(SB),NOSPLIT,$0
+	SGTU x0, y0, t0
+	SUBV x0, y0, acc0
+	// SBCS x1, y1
+	SGTU x1, y1, t1
+	SUBV x1, y1, acc1
+	SGTU t0, acc1, t2
+	SUBV t0, acc1, acc1
+	OR t1, t2, t0
+	// SBCS x2, y2
+	SGTU x2, y2, t1
+	SUBV x2, y2, acc2
+	SGTU t0, acc2, t2
+	SUBV t0, acc2, acc2
+	OR t1, t2, t0
+	// SBCS x3, y3
+	SGTU x3, y3, t1
+	SUBV x3, y3, acc3
+	SGTU t0, acc3, t2
+	SUBV t0, acc3, acc3
+	OR t1, t2, t0
+
+	MOVV $1, t1
+	MASKEQZ t0, t1, t1
+	MOVV p256one<>+0x08(SB), t2
+	MASKEQZ t0, t2, t3
+	ADDV $1, t2, t2
+	MASKEQZ t0, t2, t2
+
+	SGTU t1, acc0, t4
+	SUBV t1, acc0, x0
+	ADDV t1, t3, t3       // no carry
+	SGTU t3, acc1, t1
+	SUBV t3, acc1, x1
+	SGTU t1, acc2, t4
+	SUBV t1, acc2, x2
+	ADDV t4, t2, t1       // no carry
+	SUBV t1, acc3, x3
+
 	RET

internal/sm2ec/sm2p256_asm_loong64.go

@@ -53,3 +53,6 @@ func p256FromMont(res, in *p256Element)
 //
 //go:noescape
 func p256OrdReduce(s *p256OrdElement)
+
+//go:noescape
+func p256Sub(res, in1, in2 *p256Element)

internal/sm2ec/sm2p256_asm_loong64_test.go

@@ -258,3 +258,35 @@ func TestP256OrdReduce(t *testing.T) {
 		t.Errorf("p256OrdReduce failed for s == p256Ord+1: got %x, want %x", s2, one)
 	}
 }
+
+func TestP256Sub(t *testing.T) {
+	// in1 > in2
+	in1 := p256Element{5, 0, 0, 0}
+	in2 := p256Element{3, 0, 0, 0}
+	var res p256Element
+	p256Sub(&res, &in1, &in2)
+	want := p256Element{2, 0, 0, 0}
+	if !reflect.DeepEqual(res, want) {
+		t.Errorf("in1 > in2: got %v, want %v", res, want)
+	}
+
+	// in1 == in2
+	in1 = p256Element{7, 8, 9, 10}
+	in2 = p256Element{7, 8, 9, 10}
+	p256Sub(&res, &in1, &in2)
+	want = p256Element{0, 0, 0, 0}
+	if !reflect.DeepEqual(res, want) {
+		t.Errorf("in1 == in2: got %v, want %v", res, want)
+	}
+
+	// in1 < in2
+	in1 = p256Element{1, 0, 0, 0}
+	in2 = p256Element{2, 0, 0, 0}
+	p256Sub(&res, &in1, &in2)
+	// 1 - 2 mod 2^64 = 0xFFFFFFFFFFFFFFFF
+	want = p256Element{0xfffffffffffffffe, 0xffffffff00000000,
+		0xffffffffffffffff, 0xfffffffeffffffff}
+	if !reflect.DeepEqual(res, want) {
+		t.Errorf("in1 < in2: got %v, want %v", res, want)
+	}
+}