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Add option to use smaller AES tables (table sizes reduced by 6144 bytes)

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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
This commit is contained in:
Jussi Kivilinna 2015-11-12 16:38:31 +02:00 • committed by Hanno Becker
parent ddc6e52cc1
commit 2fd1bb8f02
3 changed files with 106 additions and 46 deletions
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3
library/version_features.c
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@ -198,6 +198,9 @@ static const char *features[] = {
#if defined(MBEDTLS_AES_ROM_TABLES)
"MBEDTLS_AES_ROM_TABLES",
#endif /* MBEDTLS_AES_ROM_TABLES */
#if defined(MBEDTLS_AES_SMALL_TABLES)
"MBEDTLS_AES_SMALL_TABLES",
#endif /* MBEDTLS_AES_SMALL_TABLES */
#if defined(MBEDTLS_CAMELLIA_SMALL_MEMORY)
"MBEDTLS_CAMELLIA_SMALL_MEMORY",
#endif /* MBEDTLS_CAMELLIA_SMALL_MEMORY */