Add option to use smaller AES tables (table sizes reduced by 6144 bytes)
This patch adds MBEDTLS_AES_SMALL_TABLES option to reduce number of AES
look-up tables and thus save 6 KiB of memory. Enabling this option
cause performance hit MBEDTLS_AES_SMALL_TABLES of ~7% on ARM and ~15%
on x86-64.
Benchmark on Cortex-A7 (armhf):
Before:
AES-CBC-128 : 14394 Kb/s, 0 cycles/byte
AES-CBC-192 : 12442 Kb/s, 0 cycles/byte
AES-CBC-256 : 10958 Kb/s, 0 cycles/byte
After:
AES-CBC-128 : 13342 Kb/s, 0 cycles/byte
AES-CBC-192 : 11469 Kb/s, 0 cycles/byte
AES-CBC-256 : 10058 Kb/s, 0 cycles/byte
Benchmark on Intel Core i5-4570 (x86_64, 3.2 Ghz, no turbo):
Before:
AES-CBC-128 : 215759 Kb/s, 14 cycles/byte
AES-CBC-192 : 190884 Kb/s, 16 cycles/byte
AES-CBC-256 : 171536 Kb/s, 18 cycles/byte
After:
AES-CBC-128 : 185108 Kb/s, 16 cycles/byte
AES-CBC-192 : 162839 Kb/s, 19 cycles/byte
AES-CBC-256 : 144700 Kb/s, 21 cycles/byte
2fd1bb8f02