issue/130: add omp cpu

src/infiniop/ops/gemm/cpu/gemm_cpu.cc

@@ -42,10 +42,14 @@ void calculate(
     if (info.is_transed) {
         std::swap(a, b);
     }
-
-    for (size_t i = 0; i < info.batch; ++i) {
-        for (size_t m_ = 0; m_ < info.m; ++m_) {
-            for (size_t n_ = 0; n_ < info.n; ++n_) {
+#pragma omp parallel for
+    for(ptrdiff_t index = 0; index < ptrdiff_t(info.batch * info.m * info.n); ++index){
+        size_t ind = index;
+        size_t n_ = ind % info.n;
+        ind /= info.n;
+        size_t m_ = ind % info.m;
+        ind /= info.m;
+        size_t i = ind;
         auto c_ = reinterpret_cast<Tdata *>(c) + i * info.c_matrix.stride + m_ * info.c_matrix.row_stride + n_ * info.c_matrix.col_stride;
         float sum = 0;
         for (size_t k_ = 0; k_ < info.k; ++k_) {
@@ -67,8 +71,6 @@ void calculate(
             *c_ = beta * (*c_) + alpha * sum;
         }
     }
-        }
-    }
 }
 
 infiniStatus_t Descriptor::calculate(