support e2m1fn

jax/_src/dtypes.py

@@ -110,6 +110,12 @@ def type(self) -> type: ...
 _float8_e5m2_dtype: np.dtype = np.dtype(float8_e5m2)
 _float8_e5m2fnuz_dtype: np.dtype = np.dtype(float8_e5m2fnuz)
 
+#fp4 support
+# TODO: remove Optional when minimum ml_dtypes version >= 0.5.0
+_float4_e2m1fn: type[np.generic] | None = None
+
+_float4_e2m1fn_dtype: np.dtype | None = None
+
 def supports_inf(dtype: DTypeLike) -> bool:
   """Return true if the dtype supports infinity, else return False."""
   typ = np.dtype(dtype).type
@@ -145,6 +151,9 @@ def supports_inf(dtype: DTypeLike) -> bool:
     _float8_e5m2fnuz_dtype,
 ]
 
+_float4_dtypes = [
+]
+
 # TODO: remove the if statements below when minimum ml_dtypes version >= 0.5.0
 if hasattr(ml_dtypes, "float8_e4m3"):
   float8_e4m3 = ml_dtypes.float8_e4m3
@@ -164,6 +173,12 @@ def supports_inf(dtype: DTypeLike) -> bool:
   _custom_float_scalar_types.insert(0, float8_e8m0fnu)  # type: ignore[arg-type]
   _custom_float_dtypes.insert(0, _float8_e8m0fnu_dtype)
   _float8_dtypes.insert(0, _float8_e8m0fnu_dtype)
+if hasattr(ml_dtypes, "float4_e2m1fn"):
+  float4_e2m1fn = ml_dtypes.float4_e2m1fn
+  _float4_e2m1fn_dtype = np.dtype(float4_e2m1fn)
+  _custom_float_scalar_types.insert(0, float4_e2m1fn)  # type: ignore[arg-type]
+  _custom_float_dtypes.insert(0, _float4_e2m1fn_dtype)
+  _float4_dtypes.insert(0, _float4_e2m1fn_dtype)
 
 # 2-bit integer support
 int2: type[np.generic] | None = None

jax/_src/export/serialization.fbs

@@ -75,6 +75,7 @@ enum DType: byte {
   f8_e5m2 = 20,
   f8_e5m2fnuz = 21,
   f8_e8m0fnu = 25,
+  f4_e2m1fn = 26,
 }
 
 table AbstractValue {

jax/_src/export/serialization.py

@@ -365,6 +365,8 @@ def _deserialize_pytreedef_to_pytree(p: ser_flatbuf.PyTreeDef):
   _dtype_to_dtype_kind[dtypes._float8_e4m3_dtype] = ser_flatbuf.DType.f8_e4m3
 if dtypes._float8_e8m0fnu_dtype is not None:
   _dtype_to_dtype_kind[dtypes._float8_e8m0fnu_dtype] = ser_flatbuf.DType.f8_e8m0fnu
+if dtypes._float4_e2m1fn_dtype is not None:
+  _dtype_to_dtype_kind[dtypes._float4_e2m1fn_dtype] = ser_flatbuf.DType.f4_e2m1fn
 _dtype_kind_to_dtype = {
     kind: dtype for dtype, kind in _dtype_to_dtype_kind.items()
 }

jax/_src/export/serialization_generated.py

@@ -62,6 +62,7 @@ class DType(object):
     f8_e5m2fnuz = 21
     f0 = 22
     f8_e8m0fnu = 25
+    f4_e2m1fn = 26
 
 
 class ShardingKind(object):

jax/_src/interpreters/mlir.py

@@ -201,6 +201,9 @@ def _is_ir_values(x: IrValues) -> bool:
 if dtypes.float8_e8m0fnu is not None:
   _dtype_to_ir_type[np.dtype(dtypes.float8_e8m0fnu)] = ir.Float8E8M0FNUType.get
 
+if dtypes.float4_e2m1fn is not None:
+  _dtype_to_ir_type[np.dtype(dtypes.float4_e2m1fn)] = ir.Float4E2M1FNType.get
+
 def dtype_to_ir_type(dtype: core.bint | np.dtype | np.generic) -> ir.Type:
   if isinstance(dtype, core.bint):
     # TODO Support different-size underlying dtypes to take advantage of the

jax/_src/public_test_util.py

@@ -100,6 +100,9 @@ def default_tolerance():
 if _dtypes.float8_e8m0fnu is not None:
   _default_tolerance[np.dtype(_dtypes.float8_e8m0fnu)] = 1e0
   default_gradient_tolerance[np.dtype(_dtypes.float8_e8m0fnu)] = 1e0
+if _dtypes.float4_e2m1fn is not None:
+  _default_tolerance[np.dtype(_dtypes.float4_e2m1fn)] = 1e0
+  default_gradient_tolerance[np.dtype(_dtypes.float4_e2m1fn)] = 1e0
 
 def is_python_scalar(val):
   return not isinstance(val, np.generic) and isinstance(val, (bool, int, float, complex))
@@ -124,6 +127,8 @@ def _assert_numpy_allclose(a, b, atol=None, rtol=None, err_msg=''):
     custom_float_dtypes.insert(0, _dtypes.float8_e3m4)
   if _dtypes.float8_e8m0fnu is not None:
     custom_float_dtypes.insert(0, _dtypes.float8_e8m0fnu)
+  if _dtypes.float4_e2m1fn is not None:
+    custom_float_dtypes.insert(0, _dtypes.float4_e2m1fn)
 
   def maybe_upcast(x):
     if x.dtype in custom_float_dtypes:

jax/_src/test_util.py

@@ -1621,6 +1621,8 @@ def custom_floats(self):
       float_dtypes += [_dtypes.float8_e4m3]
     if _dtypes.float8_e8m0fnu is not None:
       float_dtypes += [_dtypes.float8_e8m0fnu]
+    if _dtypes.float4_e2m1fn is not None:
+      float_dtypes += [_dtypes.float4_e2m1fn]
     return self.supported(float_dtypes)
 
   @_cached_property

jax/numpy/__init__.py

@@ -301,6 +301,7 @@
     float8_e3m4 as float8_e3m4,
     float8_e4m3 as float8_e4m3,
     float8_e8m0fnu as float8_e8m0fnu,
+    float4_e2m1fn as float4_e2m1fn,
   )
 except ImportError:
   pass

tests/dtypes_test.py

@@ -73,6 +73,12 @@
 float_dtypes += fp8_dtypes
 custom_float_dtypes += fp8_dtypes
 
+fp4_dtypes = []
+if dtypes.float4_e2m1fn is not None:
+  fp4_dtypes += [np.dtype(dtypes.float4_e2m1fn)]
+float_dtypes += fp4_dtypes
+custom_float_dtypes += fp4_dtypes
+
 complex_dtypes = [np.dtype('complex64'), np.dtype('complex128')]