fix(python_module): fix conversion between numpy-ndarray and mgb tensor for qint4 and quint4

GitOrigin-RevId: 7450c4f25e52fc334344b7853c0bd897a6212847

dnn/include/megdnn/oprs/base.h

@@ -90,6 +90,7 @@ enum class AlgoDataType : uint32_t {
     INT8X8X16 = 1 << 4,
     INT16X16X32 = 1 << 5,
     INT4X4X16 = 1 << 6,
+    QINT4x4x32 = 1 << 7, 
 };
 
 /*!

dnn/src/fallback/convolution/opr_impl.cpp

@@ -434,6 +434,8 @@ ConvolutionImpl::NCBKernSizeParam::deduce_algo_data_type() const {
         }
     } else if (src_type.enumv() == DTypeEnum::Quantized8Asymm) {
         return ConvolutionImpl::AlgoDataType::QUINT8X8X32;
+    } else if (src_type.enumv() == DTypeEnum::QuantizedS4) {
+        return ConvolutionImpl::AlgoDataType::QINT4x4x32;
     } else {
         megdnn_throw(ssprintf("not support data type of %s * %s -> %s\n",
                               src_type.name(), filter_type.name(),

src/core/impl/dtype.cpp

@@ -14,7 +14,6 @@
 #include "megbrain/exception.h"
 #include "megbrain/utils/metahelper.h"
 #include "megbrain/utils/arith_helper.h"
-#include "megdnn/dtype.h"
 
 #include <cmath>
 #include <cstring>
@@ -383,24 +382,40 @@ struct QuantizedLowbitMemcpy<DT, true> {
     // cast with bits that 8 % bits == 0
     static constexpr uint16_t bits = DTypeTrait<DT>::low_bit;
     static constexpr uint8_t MASK = (1 << bits) - 1;
-    using Trait = QuantizedLowbitTrait<DT>;
+    static constexpr bool signedness =
+            std::is_same<DT, dtype::QuantizedS4>::value;
 
     static void byte2compact(void* dest_raw, const void* src_raw, size_t n) {
         auto dest = static_cast<uint8_t*>(dest_raw);
         auto src = static_cast<const int8_t*>(src_raw);
         memset(dest, 0, divup<size_t>(n * bits, 8));
         for (size_t i = 0; i < n; ++i) {
-            int8_t val = src[i] + Trait::SHIFT;
-            mgb_assert(val >= 0 && val < (1 << bits));
-            dest[i * bits / 8] |= val << (i * bits % 8);
+            int8_t val = src[i];
+            static const auto min_val = DTypeTrait<DT>::min();
+            static const auto max_val = DTypeTrait<DT>::max();
+            MGB_MARK_USED_VAR(min_val);
+            MGB_MARK_USED_VAR(max_val);
+            mgb_assert(val >= static_cast<int8_t>(min_val) &&
+                               val <= static_cast<int8_t>(max_val),
+                       "data exceeds range(%d,%d) of data type", min_val,
+                       max_val);
+            dest[i * bits / 8] |= (val & MASK) << (i * bits % 8);
         }
     }
     static void compact2byte(void* dest_raw, const void* src_raw, size_t n) {
-        auto dest = static_cast<int8_t*>(dest_raw);
+        auto dest = reinterpret_cast<int8_t*>(dest_raw);
         auto src = static_cast<const uint8_t*>(src_raw);
         for (size_t i = 0; i < n; ++i) {
-            int8_t val = ((src[i * bits / 8] >> (i * bits % 8)) & MASK);
-            dest[i] = val - Trait::SHIFT;
+            uint8_t intermediate =
+                    ((src[i * bits / 8] >> (i * bits % 8)) & MASK);
+            if (signedness) {
+                int val = (intermediate & uint8_t(1 << (bits - 1)))
+                                  ? ((int)(intermediate) | ~(int)(MASK))
+                                  : (int)(intermediate);
+                dest[i] = static_cast<int8_t>(val);
+            } else {
+                dest[i] = static_cast<int8_t>(intermediate);
+            }
         }
     }
 };