code: def create_min_lower_func(extern_func_map, type_name):
      """Returns a lowering function for getting the minimum value of a custom datatype.
  
      Parameters
      ----------
      extern_func_map : map
          A map from bit lengths to the name of the extern "C" function to lower to.
  
      type_name : string
          The name of the custom datatype, e.g. posites2 (but not custom[posites2]32).
      """
  
      def lower(num_bits):
          dtype = f"custom[{type_name}]{num_bits}"
  
          if num_bits not in extern_func_map:
              raise RuntimeError("missing minimum function for {dtype}")
  
          return call_pure_extern(dtype, extern_func_map[num_bits])
  
      return lower
  
file_path: tvm/python/tvm/target/datatype.py
imports: import tvm
  from tvm.runtime import convert, DataType
  from tvm.tir.expr import Call, Cast, FloatImm, BinaryOpExpr
  from tvm.tir.op import call_pure_extern
  from tvm._ffi import register_func
  from tvm.tir import call_intrin
label_desc: Use image node_id 7 for calling a global function with example usage: create_min_lower_func(extern_func_map, type_name) and returns: lower, call_pure_extern