code: def _mask(x, dims, alternative=0):
      """Masks `x` up to the dynamic shape `dims`.
  
      Replaces values outside those dimensions with `alternative`. `alternative` is
      broadcast with `x`.
      """
      assert jnp.ndim(x) == len(dims)
      mask = None
      for i, d in enumerate(dims):
          if d is not None:
              mask_dim_i = (
                  lax.broadcasted_iota(jnp.int32, x.shape, i) < d
              )
              mask = mask_dim_i if mask is None else (mask & mask_dim_i)
      return x if mask is None else jnp.where(mask, x, alternative)
  
file_path: jax/jax/_src/lax/qdwh.py
imports: from __future__ import annotations
  import functools
  import jax
  import jax.numpy
  from jax import lax
  from jax._src import core
  from jax._src.lax import linalg
label_desc: Use image node_id 1 for calling a global function with example usage: _mask(x, dims, alternative) and returns: unknown