1 files changed, 67 insertions, 8 deletions

diff --git a/fixedpoint/fixedpoint_msa.h b/fixedpoint/fixedpoint_msa.h
index c7a110c..b17f32a 100644
--- a/fixedpoint/fixedpoint_msa.h
+++ b/fixedpoint/fixedpoint_msa.h
@@ -25,13 +25,13 @@ namespace gemmlowp {
 template <>
 struct FixedPointRawTypeTraits<v4i32> {
   typedef std::int32_t ScalarRawType;
-  static const int kLanes = 4;
+  static constexpr int kLanes = 4;
 };
 
 template <>
 struct FixedPointRawTypeTraits<v8i16> {
   typedef std::int16_t ScalarRawType;
-  static const int kLanes = 8;
+  static constexpr int kLanes = 8;
 };
 
 template <>
@@ -326,11 +326,71 @@ struct ImplSaturatingRoundingMultiplyByPOT<Exponent, v8i16, 1> {
   }
 };
 
-// TODO: possibly implement:
-// template <> v4i32 RoundingDivideByPOT(v4i32, int)
-// template <> v8i16 RoundingDivideByPOT(v8i16, int)
-// template <int Exponent> struct ImplSaturatingRoundingMultiplyByPOT<Exponent, v4i32, -1>
-// template <int Exponent> struct ImplSaturatingRoundingMultiplyByPOT<Exponent, v8i16, -1>
+template <int Exponent>
+struct ImplSaturatingRoundingMultiplyByPOT<Exponent, v4i32, -1> {
+  static v4i32 eval(v4i32 x) {
+    static_assert(-31 <= Exponent && Exponent <= -1, "");
+    // Isolate the sign bits.
+    v4i32 sign = __builtin_msa_srli_w(x, 31);
+    // Decrement the negative elements by 1 (with saturation).
+    x = __builtin_msa_subs_s_w(x, sign);
+    // Arithmetic shift right with rounding.
+    // The srari instruction rounds all midpoint values towards +infinity.
+    // It will correctly round negative midpoint values as we just
+    // decremented the negative values by 1.
+    return __builtin_msa_srari_w(x, -Exponent);
+  }
+};
+
+template <int Exponent>
+struct ImplSaturatingRoundingMultiplyByPOT<Exponent, v8i16, -1> {
+  static v8i16 eval(v8i16 x) {
+    static_assert(-15 <= Exponent && Exponent <= -1, "");
+    // Isolate the sign bits.
+    v8i16 sign = __builtin_msa_srli_h(x, 15);
+    // Decrement the negative elements by 1 (with saturation).
+    x = __builtin_msa_subs_s_h(x, sign);
+    // Arithmetic shift right with rounding.
+    // The srari instruction rounds all midpoint values towards +infinity.
+    // It will correctly round negative midpoint values as we just
+    // decremented the negative values by 1.
+    return __builtin_msa_srari_h(x, -Exponent);
+  }
+};
+
+template <>
+inline v4i32 RoundingDivideByPOT(v4i32 x, int exponent) {
+  v4i32 e = __builtin_msa_fill_w(exponent);
+  // Isolate the sign bits.
+  v4i32 sign = __builtin_msa_srli_w(x, 31);
+  // Reset them to 0 if exponent is 0.
+  sign = __builtin_msa_min_s_w(sign, e);
+  // Decrement the negative elements by 1 (with saturation)
+  // if exponent is non-zero.
+  x = __builtin_msa_subs_s_w(x, sign);
+  // Arithmetic shift right with rounding.
+  // The srar instruction rounds all midpoint values towards +infinity.
+  // It will correctly round negative midpoint values as we just
+  // decremented the negative values by 1.
+  return __builtin_msa_srar_w(x, e);
+}
+
+template <>
+inline v8i16 RoundingDivideByPOT(v8i16 x, int exponent) {
+  v8i16 e = __builtin_msa_fill_h(exponent);
+  // Isolate the sign bits.
+  v8i16 sign = __builtin_msa_srli_h(x, 15);
+  // Reset them to 0 if exponent is 0.
+  sign = __builtin_msa_min_s_h(sign, e);
+  // Decrement the negative elements by 1 (with saturation)
+  // if exponent is non-zero.
+  x = __builtin_msa_subs_s_h(x, sign);
+  // Arithmetic shift right with rounding.
+  // The srar instruction rounds all midpoint values towards +infinity.
+  // It will correctly round negative midpoint values as we just
+  // decremented the negative values by 1.
+  return __builtin_msa_srar_h(x, e);
+}
 
 template <>
 inline v4i32 Dup<v4i32>(std::int32_t x) {
@@ -346,7 +406,6 @@ inline v8i16 Dup<v8i16>(std::int16_t x) {
 template <>
 inline v8i16 SaturatingAdd(v8i16 a, v8i16 b) {
   return __builtin_msa_adds_s_h(a, b);
-  return a;
 }
 
 }  // end namespace gemmlowp