cpu: de-duplicate some of the operators and refactor (ggml/1144)

* cpu: de-duplicate some of the operators and refactor

* Fix PR comments

* Fix PR comments

ggml/src/ggml-cpu/common.h

@@ -0,0 +1,72 @@
+#pragma once
+
+#include "ggml.h"
+#include "ggml-cpu-traits.h"
+#include "ggml-cpu-impl.h"
+#include "ggml-impl.h"
+
+#ifdef __cplusplus
+
+#include <utility>
+
+// convenience functions/macros for use in template calls
+// note: these won't be required after the 'traits' lookup table is used.
+static inline ggml_fp16_t f32_to_f16(float x) {
+    return GGML_FP32_TO_FP16(x);
+}
+
+static inline float f16_to_f32(ggml_fp16_t x) {
+    return GGML_FP16_TO_FP32(x);
+}
+
+static inline ggml_bf16_t f32_to_bf16(float x) {
+    return GGML_FP32_TO_BF16(x);
+}
+
+static inline float bf16_to_f32(ggml_bf16_t x) {
+    return GGML_BF16_TO_FP32(x);
+}
+
+static inline float f32_to_f32(float x) {
+    return x;
+}
+
+// TODO - merge this into the traits table, after using row-based conversions
+template <class T>
+struct type_conversion_table;
+
+template <>
+struct type_conversion_table<ggml_fp16_t> {
+    static constexpr float (*to_f32)(ggml_fp16_t) = f16_to_f32;
+    static constexpr ggml_fp16_t (*from_f32)(float) = f32_to_f16;
+};
+
+template <>
+struct type_conversion_table<float> {
+    static constexpr float (*to_f32)(float) = f32_to_f32;
+    static constexpr float (*from_f32)(float) = f32_to_f32;
+};
+
+template <>
+struct type_conversion_table<ggml_bf16_t> {
+    static constexpr float (*to_f32)(ggml_bf16_t) = bf16_to_f32;
+    static constexpr ggml_bf16_t (*from_f32)(float) = f32_to_bf16;
+};
+
+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;
+
+    const int64_t nr  = ggml_nrows(src0);
+
+    // rows per thread
+    const int64_t dr = (nr + nth - 1)/nth;
+
+    // row range for this thread
+    const int64_t ir0 = dr*ith;
+    const int64_t ir1 = MIN(ir0 + dr, nr);
+
+    return {ir0, ir1};
+}
+
+#endif