from numcodecs import Delta
from numcodecs.compat import ensure_ndarray
import numpy as np
import time

# new codec
class CustomDelta(Delta):
    def encode(self, buf):
        arr = ensure_ndarray(buf).view(self.dtype)
        arr = arr.reshape(-1, order='A')
        enc = np.empty_like(arr, dtype=self.astype)
        enc[0] = arr[0]

        # only difference from Delta!!
        np.subtract(arr[1:], arr[0:-1], out = enc[1:])

        return enc

data_length = int(1e9)
x = np.random.randint(0,10000,(data_length,),dtype='i4')

# benchmark
base_codec = Delta(dtype='i4')
new_codec = CustomDelta(dtype='i4')
for codec in (base_codec, new_codec):
    time_start = time.perf_counter()
    for _ in range(10):
        codec.encode(x)
    time_end = time.perf_counter()
    benchmark_time = (time_end-time_start)/10
    print(f'time of {str(codec)} = {benchmark_time:.6f}')
# time of Delta(dtype='<i4') = 1.510299
# time of CustomDelta(dtype='<i4') = 0.953429

assert np.all(base_codec.encode(x) == new_codec.encode(x)), 'They should be equal'