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avutil/aes_ctr: simplify and optimize av_aes_ctr_crypt()

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Process data in chunks of four or eight bytes, depending on host, instead of
one at a time.

before:
55561 decicycles in av_aes_ctr_crypt

after:
52204 decicycles in av_aes_ctr_crypt

Signed-off-by: James Almer <jamrial@gmail.com>
This commit is contained in:
James Almer
2025-04-01 12:08:12 -03:00
parent 2ea3c51795
commit fe73b84879
1 changed files with 21 additions and 26 deletions
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47
libavutil/aes_ctr.c
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@ -24,6 +24,7 @@
#include "aes_ctr.h"
#include "aes.h"
#include "aes_internal.h"
#include "intreadwrite.h"
#include "macros.h"
#include "mem.h"
#include "random_seed.h"
@ -32,8 +33,7 @@
typedef struct AVAESCTR {
uint8_t counter[AES_BLOCK_SIZE];
uint8_t encrypted_counter[AES_BLOCK_SIZE];
int block_offset;
DECLARE_ALIGNED(8, uint8_t, encrypted_counter)[AES_BLOCK_SIZE];
AVAES aes;
} AVAESCTR;
@ -46,13 +46,11 @@ void av_aes_ctr_set_iv(struct AVAESCTR *a, const uint8_t* iv)
{
memcpy(a->counter, iv, AES_CTR_IV_SIZE);
memset(a->counter + AES_CTR_IV_SIZE, 0, sizeof(a->counter) - AES_CTR_IV_SIZE);
a->block_offset = 0;
}
void av_aes_ctr_set_full_iv(struct AVAESCTR *a, const uint8_t* iv)
{
memcpy(a->counter, iv, sizeof(a->counter));
a->block_offset = 0;
}
const uint8_t* av_aes_ctr_get_iv(struct AVAESCTR *a)
@ -75,7 +73,6 @@ int av_aes_ctr_init(struct AVAESCTR *a, const uint8_t *key)
av_aes_init(&a->aes, key, 128, 0);
memset(a->counter, 0, sizeof(a->counter));
a->block_offset = 0;
return 0;
}
@ -101,31 +98,29 @@ void av_aes_ctr_increment_iv(struct AVAESCTR *a)
{
av_aes_ctr_increment_be64(a->counter);
memset(a->counter + AES_CTR_IV_SIZE, 0, sizeof(a->counter) - AES_CTR_IV_SIZE);
a->block_offset = 0;
}
void av_aes_ctr_crypt(struct AVAESCTR *a, uint8_t *dst, const uint8_t *src, int count)
{
const uint8_t* src_end = src + count;
const uint8_t* cur_end_pos;
uint8_t* encrypted_counter_pos;
while (count >= AES_BLOCK_SIZE) {
av_aes_crypt(&a->aes, a->encrypted_counter, a->counter, 1, NULL, 0);
av_aes_ctr_increment_be64(a->counter + 8);
#if HAVE_FAST_64BIT
for (int len = 0; len < AES_BLOCK_SIZE; len += 8)
AV_WN64(&dst[len], AV_RN64(&src[len]) ^ AV_RN64A(&a->encrypted_counter[len]));
#else
for (int len = 0; len < AES_BLOCK_SIZE; len += 4)
AV_WN32(&dst[len], AV_RN32(&src[len]) ^ AV_RN32A(&a->encrypted_counter[len]));
#endif
dst += AES_BLOCK_SIZE;
src += AES_BLOCK_SIZE;
count -= AES_BLOCK_SIZE;
}
while (src < src_end) {
if (a->block_offset == 0) {
av_aes_crypt(&a->aes, a->encrypted_counter, a->counter, 1, NULL, 0);
av_aes_ctr_increment_be64(a->counter + 8);
}
encrypted_counter_pos = a->encrypted_counter + a->block_offset;
cur_end_pos = src + AES_BLOCK_SIZE - a->block_offset;
cur_end_pos = FFMIN(cur_end_pos, src_end);
a->block_offset += cur_end_pos - src;
a->block_offset &= (AES_BLOCK_SIZE - 1);
while (src < cur_end_pos) {
*dst++ = *src++ ^ *encrypted_counter_pos++;
}
if (count > 0) {
av_aes_crypt(&a->aes, a->encrypted_counter, a->counter, 1, NULL, 0);
av_aes_ctr_increment_be64(a->counter + 8);
for (int len = 0; len < count; len++)
dst[len] = src[len] ^ a->encrypted_counter[len];
}
}