ggml : refactor forward_dup for cpu backend (ggml-org#16062)

* ggml : refactor forward_dup for cpu backend

* clean up a bit

* add quant/dequant perf test

Author: ngxson

ggml/src/ggml-cpu/common.h

@@ -28,6 +28,14 @@ static inline float bf16_to_f32(ggml_bf16_t x) {
     return GGML_BF16_TO_FP32(x);
 }
 
+static inline float i32_to_f32(int32_t x) {
+    return x;
+}
+
+static inline int32_t f32_to_i32(float x) {
+    return x;
+}
+
 static inline float f32_to_f32(float x) {
     return x;
 }
@@ -54,6 +62,12 @@ struct type_conversion_table<ggml_bf16_t> {
     static constexpr ggml_bf16_t (*from_f32)(float) = f32_to_bf16;
 };
 
+template <>
+struct type_conversion_table<int32_t> {
+    static constexpr float (*to_f32)(int32_t) = i32_to_f32;
+    static constexpr int32_t (*from_f32)(float) = f32_to_i32;
+};
+
 static std::pair<int64_t, int64_t> get_thread_range(const struct ggml_compute_params * params, const struct ggml_tensor * src0) {
     const int64_t ith = params->ith;
     const int64_t nth = params->nth;