llama : fix integer overflow during quantization (#4284)

happens with multi-threaded quantization of Qwen-72B

ggml-ci

Author: ggerganov

llama.cpp

@@ -7655,18 +7655,21 @@ static void llama_convert_tensor_internal(
         return;
     }
 
-    auto block_size = tensor->type == GGML_TYPE_F16 ? 1 : (size_t)ggml_blck_size(tensor->type);
-    auto block_size_bytes = ggml_type_size(tensor->type);
+    size_t block_size = tensor->type == GGML_TYPE_F16 ? 1 : (size_t)ggml_blck_size(tensor->type);
+    size_t block_size_bytes = ggml_type_size(tensor->type);
 
     GGML_ASSERT(nelements % block_size == 0);
-    auto nblocks = nelements / block_size;
-    auto blocks_per_thread = nblocks / nthread;
-    auto spare_blocks = nblocks - (blocks_per_thread * nthread); // if blocks aren't divisible by thread count
-
-    for (auto tnum = 0, in_buff_offs = 0, out_buff_offs = 0; tnum < nthread; tnum++) {
-        auto thr_blocks = blocks_per_thread + (tnum == nthread - 1 ? spare_blocks : 0); // num blocks for this thread
-        auto thr_elems = thr_blocks * block_size; // number of elements for this thread
-        auto thr_block_bytes = thr_blocks * block_size_bytes; // number of input bytes for this thread
+    size_t nblocks = nelements / block_size;
+    size_t blocks_per_thread = nblocks / nthread;
+    size_t spare_blocks = nblocks - (blocks_per_thread * nthread); // if blocks aren't divisible by thread count
+
+    size_t in_buff_offs = 0;
+    size_t out_buff_offs = 0;
+
+    for (int tnum = 0; tnum < nthread; tnum++) {
+        size_t thr_blocks = blocks_per_thread + (tnum == nthread - 1 ? spare_blocks : 0); // num blocks for this thread
+        size_t thr_elems = thr_blocks * block_size; // number of elements for this thread
+        size_t thr_block_bytes = thr_blocks * block_size_bytes; // number of input bytes for this thread
 
         auto compute = [qtype] (ggml_type typ, uint8_t * inbuf, float * outbuf, int nels) {
             if (typ == GGML_TYPE_F16) {