issue/130: delete collapse

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

@@ -42,10 +42,15 @@ void calculate(
     if (info.is_transed) {
         std::swap(a, b);
     }
-#pragma omp parallel for collapse(3)
-    for (int i = 0; i < static_cast<int>(info.batch); ++i) {
-        for (int m_ = 0; m_ < static_cast<int>(info.m); ++m_) {
-            for (int n_ = 0; n_ < static_cast<int>(info.n); ++n_) {
+    const size_t m_n = info.m * info.n;
+    const size_t n = info.n;
+#pragma omp parallel for
+    for (ptrdiff_t index = 0; index < ptrdiff_t(info.batch * info.m * info.n); ++index) {
+        size_t i, m_, n_;
+        i = index / m_n;
+        size_t rem = index - i * m_n; // 替代 `%` 用减法
+        m_ = rem / n;
+        n_ = rem - m_ * n; // 替代 `%` 用减法
         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 (int k_ = 0; k_ < static_cast<int>(info.k); ++k_) {
@@ -67,8 +72,6 @@ void calculate(
             *c_ = beta * (*c_) + alpha * sum;
         }
     }
-        }
-    }
 }
 
 infiniStatus_t Descriptor::calculate(