Does using a chunk size of 4096 not forego hardware acceleration on iOS?

[mrubin]

Does anyone know why 4096 is used as the default chunk size for reading data? According to https://opensource.apple.com/source/CommonCrypto/CommonCrypto-36064/Source/Digest/sha1.c (via http://stackoverflow.com/a/5387310/1011953), SHA1 (and perhaps the other digests) is hardware accelerated if the size of the data it is given is > 4096.

For example, the average of 100 sha1's on a ~1.4MB file on a 9.7" iPad Pro:

chunk size (bytes)	time (sec)
4096	0.00042184
8192	0.00039322
12,288	0.00035151
16,384	0.00033951
20,480	0.00035334

Thank you.