add truncate_bf16

Author: CISC

gguf-py/gguf/quants.py

@@ -35,6 +35,12 @@ def __compute_fp32_to_bf16(n: np.ndarray) -> np.ndarray:
     return n.astype(np.int16)
 
 
+# for fp32 values that are just extended bf16
+def __truncate_fp32_to_bf16(n: np.ndarray) -> np.ndarray:
+    n = n.astype(np.float32, copy=False).view(np.uint32) >> 16
+    return n.astype(np.uint16)
+
+
 # This is faster than np.vectorize and np.apply_along_axis because it works on more than one row at a time
 def __apply_over_grouped_rows(func: Callable[[np.ndarray], np.ndarray], arr: np.ndarray, otype: DTypeLike, oshape: tuple[int, ...]) -> np.ndarray:
     rows = arr.reshape((-1, arr.shape[-1]))
@@ -62,6 +68,20 @@ def quantize_bf16(n: np.ndarray):
         return __quantize_bf16_array(n)
 
 
+def __truncate_bf16_array(n: np.ndarray) -> np.ndarray:
+    return __apply_over_grouped_rows(__truncate_fp32_to_bf16, arr=n, otype=np.uint16, oshape=n.shape)
+
+
+__truncate_bf16_lazy = LazyNumpyTensor._wrap_fn(__truncate_bf16_array, meta_noop=np.uint16)
+
+
+def truncate_bf16(n: np.ndarray):
+    if type(n) is LazyNumpyTensor:
+        return __truncate_bf16_lazy(n)
+    else:
+        return __truncate_bf16_array(n)
+
+
 __q8_block_size, __q8_type_size = GGML_QUANT_SIZES[GGMLQuantizationType.Q8_0]