ggml : add new Q4_2 quantization (ARM only) (#1046)

* ggml : Q4_2 ARM

* ggml : add ggml_is_quantized()

* llama : update llama_type_name() with Q4_2 entry

* ggml : speed-up q4_2

- 4 threads: ~100ms -> ~90ms
- 8 threads:  ~55ms -> ~50ms

* ggml : optimize q4_2 using vmlaq_n_f32 + vmulq_n_f32

1 files changed, 3 insertions, 1 deletions

diff --git a/ggml.h b/ggml.h
index 59de0cb..603be84 100644
--- a/ggml.h
+++ b/ggml.h
@@ -204,7 +204,8 @@ enum ggml_type {
     GGML_TYPE_F16  = 1,
     GGML_TYPE_Q4_0 = 2,
     GGML_TYPE_Q4_1 = 3,
-    GGML_TYPE_Q8_0 = 4,
+    GGML_TYPE_Q4_2 = 4,
+    GGML_TYPE_Q8_0 = 5,
     GGML_TYPE_I8,
     GGML_TYPE_I16,
     GGML_TYPE_I32,
@@ -806,6 +807,7 @@ enum ggml_opt_result ggml_opt(
 
 size_t ggml_quantize_q4_0(const float * src, void * dst, int n, int k, int64_t * hist);
 size_t ggml_quantize_q4_1(const float * src, void * dst, int n, int k, int64_t * hist);
+size_t ggml_quantize_q4_2(const float * src, void * dst, int n, int k, int64_t * hist);
 
 //
 // system info