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sys/checksum: add CRC-16 implementation without lookup table

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This commit is contained in:
Benjamin Valentin 2022-10-06 17:43:20 +02:00
parent 4493afb582
commit e313c56e94
4 changed files with 28 additions and 2 deletions
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1
makefiles/pseudomodules.inc.mk
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@ -45,6 +45,7 @@ PSEUDOMODULES += cortexm_fpu
PSEUDOMODULES += cortexm_svc PSEUDOMODULES += cortexm_svc
PSEUDOMODULES += cpp PSEUDOMODULES += cpp
PSEUDOMODULES += cpu_check_address PSEUDOMODULES += cpu_check_address
PSEUDOMODULES += crc16_fast
PSEUDOMODULES += crc32_fast PSEUDOMODULES += crc32_fast
PSEUDOMODULES += credman_load PSEUDOMODULES += credman_load
PSEUDOMODULES += dbgpin PSEUDOMODULES += dbgpin

4
sys/Makefile.dep
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@ -49,6 +49,10 @@ ifneq (,$(filter congure_reno_methods,$(USEMODULE)))
USEMODULE += seq USEMODULE += seq
endif endif
ifneq (,$(filter crc16_fast,$(USEMODULE)))
USEMODULE += checksum
endif
ifneq (,$(filter crc32_fast,$(USEMODULE))) ifneq (,$(filter crc32_fast,$(USEMODULE)))
USEMODULE += checksum USEMODULE += checksum
endif endif

22
sys/checksum/crc16_ccitt.c
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@ -21,6 +21,8 @@
#include <stdint.h> #include <stdint.h>
#include <stdlib.h> #include <stdlib.h>
#include "byteorder.h"
#include "kernel_defines.h"
#include "checksum/crc16_ccitt.h" #include "checksum/crc16_ccitt.h"
static const uint16_t crc_ccitt_lookuptable[256] = { static const uint16_t crc_ccitt_lookuptable[256] = {
@ -96,7 +98,16 @@ static const uint16_t _crc16_ccitt_false_lookuptable[256] = {
uint16_t crc16_ccitt_kermit_update(uint16_t crc, const unsigned char *buf, size_t len) uint16_t crc16_ccitt_kermit_update(uint16_t crc, const unsigned char *buf, size_t len)
{ {
while (len--) { while (len--) {
crc = (crc >> 8) ^ crc_ccitt_lookuptable[(crc ^ (*buf++)) & 0xff]; uint8_t e = crc ^= *buf++;
if (IS_USED(MODULE_CRC16_FAST)) {
crc = (crc >> 8) ^ crc_ccitt_lookuptable[e];
} else {
uint8_t f = e ^ (e << 4);
crc = (crc >> 8)
^ ((uint16_t)f << 8)
^ ((uint16_t)f << 3)
^ ((uint16_t)f >> 4);
}
} }
return crc; return crc;
@ -115,7 +126,14 @@ uint16_t crc16_ccitt_mcrf4xx_calc(const unsigned char *buf, size_t len)
uint16_t crc16_ccitt_false_update(uint16_t crc, const unsigned char *buf, size_t len) uint16_t crc16_ccitt_false_update(uint16_t crc, const unsigned char *buf, size_t len)
{ {
while (len--) { while (len--) {
crc = ((crc << 8) ^ _crc16_ccitt_false_lookuptable[((crc >> 8) ^ ((*buf++) & 0x00FF))]); crc = byteorder_swaps(crc) ^ *buf++;
if (IS_USED(MODULE_CRC16_FAST)) {
crc = (crc & 0xFF00) ^ _crc16_ccitt_false_lookuptable[crc & 0xFF];
} else {
crc ^= (uint8_t)(crc & 0xff) >> 4;
crc ^= (crc << 8) << 4;
crc ^= ((crc & 0xff) << 4) << 1;
}
} }
return crc; return crc;

3
sys/include/checksum/crc16_ccitt.h
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@ -18,6 +18,9 @@
* do (and is thus also far more memory efficient). Its caveat * do (and is thus also far more memory efficient). Its caveat
* however is that it is slower by about factor 8 than these versions. * however is that it is slower by about factor 8 than these versions.
* *
* @note enable the `crc32_fast` module for a look-up table based
* implementation that trades code size for speed.
*
* @{ * @{
* @file * @file
* @author Ludwig Knüpfer <ludwig.knuepfer@fu-berlin.de> * @author Ludwig Knüpfer <ludwig.knuepfer@fu-berlin.de>