Fix bug eclipse/aidge/aidge_backend_cpu#40

include/aidge/backend/cpu/operator/GlobalAveragePoolingImpl_kernels.hpp

@@ -25,6 +25,28 @@
 
 
 namespace Aidge {
+
+template <typename T>
+typename std::enable_if<std::is_floating_point<T>::value, T>::type
+stableMean(const T* vec, size_t size) {
+  T mean = 0;
+  for (size_t i = 0; i < size; ++i) {
+    mean = std::fma<T>(vec[i] - mean, 1.0f / (i + 1), mean);
+  }
+  return mean;
+}
+
+// Specialization for integers: perform the mean computation in float
+template <typename T>
+typename std::enable_if<!std::is_floating_point<T>::value, T>::type
+stableMean(const T* vec, size_t size) {
+  float mean = 0;
+  for (size_t i = 0; i < size; ++i) {
+    mean = std::fma<float>(vec[i] - mean, 1.0f / (i + 1), mean);
+  }
+  return mean;
+}
+
 template <class I, class O>
 void GlobalAveragePoolingImpl_cpu_forward_kernel(
     const std::vector<DimSize_t> &dims, const void *input_, void *output_) {
@@ -49,12 +71,7 @@ void GlobalAveragePoolingImpl_cpu_forward_kernel(
     for (DimSize_t channel = 0; channel < dims[1]; ++channel) {
       const I *filter_start = std::next(
           input, (batch * in_batch_nb_elems) + (channel * in_channel_nb_elems));
-      I mean = 0;
-      for (size_t i = 0; i < in_channel_nb_elems; ++i) {
-        // Single pass numerically stable mean, using the fmaf
-        mean = fmaf(filter_start[i] - mean, 1.0f/(i+1), mean);
-      }
-      output[batch * out_batch_nb_elems + channel] = mean;
+      output[batch * out_batch_nb_elems + channel] = stableMean<I>(filter_start, in_channel_nb_elems);
     }
   }
 }

include/aidge/backend/cpu/operator/ReduceMeanImpl_kernels.hpp

@@ -25,6 +25,28 @@
 #include "aidge/utils/Registrar.hpp"
 
 namespace Aidge {
+
+template <typename T>
+typename std::enable_if<std::is_floating_point<T>::value, T>::type
+stableMean(const T* vec, size_t len, size_t stride) {
+  T mean = 0;
+  for (size_t i = 0; i < len; ++i) {
+    mean = std::fma<T>(vec[i * stride] - mean, 1.0f / (i + 1), mean);
+  }
+  return mean;
+}
+
+// Specialization for integers: perform the mean computation in float
+template <typename T>
+typename std::enable_if<!std::is_floating_point<T>::value, T>::type
+stableMean(const T* vec, size_t len, size_t stride) {
+  float mean = 0;
+  for (size_t i = 0; i < len; ++i) {
+    mean = std::fma<float>(vec[i * stride] - mean, 1.0f / (i + 1), mean);
+  }
+  return mean;
+}
+
 template <class I, class O>
 void ReduceMeanImpl_cpu_forward_kernel(const std::vector<std::int32_t>& axes,
                                     DimSize_t /*keepDims*/,
@@ -50,12 +72,7 @@ void ReduceMeanImpl_cpu_forward_kernel(const std::vector<std::int32_t>& axes,
             for (std::size_t post = 0; post < stride_post; ++post) {
                 const std::size_t idx_i = pre * dim_i * stride_post + post;
                 const std::size_t idx_o = pre * stride_post + post;
-                O mean = 0;
-                for (std::size_t i = 0; i < dim_i; ++i) {
-                    // Single pass numerically stable mean, using the fmaf
-                    mean = fmaf(input[idx_i + i*stride_post] - mean, 1.0f/(i+1), mean);
-                }
-                output[idx_o]  = mean;
+                output[idx_o]  = stableMean<I>(input + idx_i, dim_i, stride_post);
             }
         }
     } else {
@@ -84,12 +101,7 @@ void ReduceMeanImpl_cpu_forward_kernel(const std::vector<std::int32_t>& axes,
                 for (std::size_t post = 0; post < stride_post[a]; ++post) {
                     const std::size_t idx_i = pre * dim_i * stride_post[a] + post;
                     const std::size_t idx_o = pre * stride_post[a] + post;
-                    I mean = 0;
-                    for (std::size_t i = 0; i < dim_i; ++i) {
-                        // Single pass numerically stable mean, using the fmaf
-                        mean = fmaf(inputAccumulation[idx_i + i*stride_post[a]] - mean, 1.0f/(i+1), mean);
-                    }
-                    outputAccumulation[idx_o] = mean;
+                    outputAccumulation[idx_o] = stableMean<I>(inputAccumulation + idx_i, dim_i, stride_post[a]);
                 }
             }
             std::for_each(stride_pre.get()+a+1, stride_pre.get()+nb_dims, [dim_i] (std::size_t& val) { val /= dim_i; });