{"record":{"id":"816825ef503f28c4","repo":"jax-ml/jax","slug":"when-changing-to-a-larger-dtype-its-size-must-be","errorCode":null,"errorMessage":"When changing to a larger dtype, its size must be a divisor of the total size in bytes of the last axis of the array.","messagePattern":"When changing to a larger dtype, its size must be a divisor of the total size in bytes of the last axis of the array\\.","errorType":"exception","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"jax/_src/numpy/array_methods.py","lineNumber":607,"sourceCode":"  \"\"\"\n  if type is not None:\n    raise NotImplementedError(\"`type` argument of array.view() is not supported.\")\n\n  if dtype is None:\n    return self\n\n  dtype = dtypes.check_and_canonicalize_user_dtype(dtype, \"view\")\n\n  nbits_in = dtypes.itemsize_bits(self.dtype)\n  nbits_out = dtypes.itemsize_bits(dtype)\n\n  if self.ndim == 0:\n    if nbits_in != nbits_out:\n      raise ValueError(\"view() of a 0d array is only supported if the itemsize is unchanged.\")\n    return _view(lax.expand_dims(self, (0,)), dtype).squeeze()\n\n  if (self.shape[-1] * nbits_in) % nbits_out != 0:\n    raise ValueError(\"When changing to a larger dtype, its size must be a divisor \"\n                     \"of the total size in bytes of the last axis of the array.\")\n\n  if self.dtype == dtype:\n    return self\n\n  # lax.bitcast_convert_type does not support bool or complex; in these cases we\n  # cast to a compatible type and recursively call _view for simplicity.\n  if self.dtype == bool:\n    return _view(self.astype('uint8'), dtype)\n\n  if lax_numpy.issubdtype(self.dtype, np.complexfloating):\n    new_shape = (*self.shape[:-1], self.shape[-1] * 2)\n    new_dtype = lax_numpy.finfo(self.dtype).dtype\n    new_sharding = core.typeof(self).sharding\n    self = (array_creation.zeros(new_shape, new_dtype, out_sharding=new_sharding)\n            .at[..., 0::2].set(self.real)\n            .at[..., 1::2].set(self.imag))\n    return _view(self, dtype)","sourceCodeStart":589,"sourceCodeEnd":625,"githubUrl":"https://github.com/jax-ml/jax/blob/1e1c6a8fc06dfcd1247076ec5cae4640cea5d7bb/jax/_src/numpy/array_methods.py#L589-L625","documentation":"When viewing an array as a dtype with a different itemsize, the last axis's total size in bits must be divisible by the new itemsize so elements map cleanly. This mirrors NumPy's rule for larger dtypes: the last axis must be divisible in bytes by the new itemsize.","triggerScenarios":"`arr.view(dtype)` where (arr.shape[-1] * itemsize_bits(arr.dtype)) % itemsize_bits(dtype) != 0, e.g. a float32 array of shape (3,) viewed as float64 (12 bytes / 8 not integral), or shape (3,) uint8 viewed as uint32.","commonSituations":"Bit-reinterpreting packed feature vectors whose length doesn't align to the new type; viewing images (H, W, 3) uint8 as a wider type.","solutions":["Pad or trim the last axis so its byte-length is divisible by the new itemsize (e.g. pad to multiple of 4 before uint8->uint32 view)","View to the same-itemsize dtype first, then reshape","Reshape so the last axis has a compatible length before viewing"],"exampleFix":"# before\na = jnp.zeros((3,), jnp.float32)\na.view(jnp.float64)  # 12 bytes not divisible by 8\n\n# after\na = jnp.zeros((4,), jnp.float32)\na.view(jnp.float64)  # shape (2,)","handlingStrategy":"validation","validationCode":"def view_dtype(a, dtype):\n    from jax import dtypes\n    out_bits = dtypes.itemsize_bits(dtype)\n    assert (a.shape[-1] * dtypes.itemsize_bits(a.dtype)) % out_bits == 0, \\\n        'last axis bits not divisible by new itemsize'\n    return a.view(dtype)","typeGuard":null,"tryCatchPattern":null,"preventionTips":["Ensure last-axis byte length is a multiple of the new itemsize","Pad to alignment before widening dtype views"],"tags":["jax","view","dtype","alignment"],"backgroundTag":"unsupported-dtype-conversion","analyzedSha":"1e1c6a8fc06dfcd1247076ec5cae4640cea5d7bb","analyzedAt":"2026-08-27T09:53:25.647Z","schemaVersion":2},"datasetVersion":"2026-08-27T13:17:12.746Z"}