#include <stdio.h>
#include <stdint.h>
#define N_FAST_FORWARD_TABLES 4
#define N_FAST_FORWARD_TABLE_ENTRIES 16
#define CRC16_INIT_STATE 0xFFFFU
#define CRC16_POLYNOMIAL 0x1021U
#define CRC16_INIT_STATE 0xFFFFU
unsigned short ffwTables[N_FAST_FORWARD_TABLES * N_FAST_FORWARD_TABLE_ENTRIES];
unsigned short ffwLutSteps[N_FAST_FORWARD_TABLES] = { 250, 120, 60, 30 };
unsigned short crcTable[256];
uint16_t calc_two_reg_crc16_table256(const uint8_t* msg, const uint32_t len) {
uint32_t crc = CRC16_INIT_STATE;
const uint8_t *msgEnd = msg + len;
while (msg < msgEnd) {
// next lined will perform: crc = (crc << 8) ^ crcTable[(crc >> 8) ^ *msg];
// operations are written to guide compiler for a two operands machine
uint32_t feedback;
uint32_t tableIdx;
tableIdx = crc;
tableIdx >>= 8U;
tableIdx ^= *msg;
tableIdx &= 0xffU;
feedback = crcTable[tableIdx]; // V850 requires one instruction between load and usage of data
crc <<= 8U;
crc ^= feedback;
// increment message read pointer for next round
msg++;
} // loop costs 4 cycles (1 cycle cmp + 3 branch) on V850
return ((uint16_t)crc);
}
uint16_t calc_two_reg_crc16_fast_forward(uint16_t ffwTable[16], uint16_t crcIn) {
int32_t idx;
uint32_t crcOut = 0U;
for (idx = 15; idx >= 0; idx--) { // running backwards to reduce V850 loop overhead
if (((crcIn >> (uint32_t)idx) & 0x1U) != 0U) {
crcOut ^= ffwTable[idx];
}
}
return ((uint16_t)crcOut);
}
uint16_t calc_two_reg_crc16_forward(uint32_t crc, uint32_t len) {
while (len > 0U) {
// next lined will perform: crc = (crc << 8) ^ crcTable[(crc >> 8)];
// operations are written to guide compiler for a two operands machine
uint32_t feedback;
uint32_t tableIdx;
tableIdx = crc;
tableIdx >>= 8U;
tableIdx &= 0xffU;
feedback = crcTable[tableIdx]; // V850 requires one instruction between load and usage of data
crc <<= 8U;
crc ^= feedback;
len--;
} // loop costs 4 cycles (1 cycle cmp + 3 branch) on V850
return (uint16_t)crc;
}
uint16_t calc_spi_frame_crc(const uint8_t* pFrame, uint32_t frameLen, const uint32_t usedLen) {
uint16_t crcState = 0;
if (frameLen >= usedLen) {
int32_t idx;
uint16_t * pffwTable = ffwTables;
crcState = calc_two_reg_crc16_table256(pFrame, usedLen);
frameLen -= usedLen;
for (idx = 0; idx < N_FAST_FORWARD_TABLES; idx++) {
uint32_t lutSteps = ffwLutSteps[idx];
if (lutSteps <= frameLen) {
crcState = calc_two_reg_crc16_fast_forward(&pffwTable[idx * N_FAST_FORWARD_TABLE_ENTRIES], crcState);
frameLen -= lutSteps;
}
}
crcState = calc_two_reg_crc16_forward((uint32_t)crcState, frameLen);
}
else
{
// TODO: implement platform specific error handling
}
return ~crcState;
}
static inline void addCRC(const uint32_t usedSize, const uint32_t size, uint8_t* const pMOSIframe) {
uint16_t crc;
crc = calc_spi_frame_crc(pMOSIframe, size - 2u, usedSize);
//typecasting from higher to narrower range is fine here since using only narrow bit range.
pMOSIframe[size - 1u] = (uint8_t)crc & 0xffu;
pMOSIframe[size - 2u] = (uint8_t)(crc >> 8u);
}
void two_reg_crc16FastForwardTableGen(uint16_t table[16], uint32_t n_bytes) {
uint16_t bitIdx;
for (bitIdx = 0; bitIdx < 16U; bitIdx++) {
uint32_t crcState;
crcState = (uint32_t)((uint32_t)1u << ((uint32_t)bitIdx));
table[bitIdx] = calc_two_reg_crc16_forward(crcState, n_bytes);
}
}
uint16_t calcByteCrc16Bitwise(uint32_t crc, uint32_t inByte) {
uint32_t poly = CRC16_POLYNOMIAL;
uint32_t idx;
uint32_t bitMask = 0x10000U;
inByte = inByte << 8U;
for (idx = 0U; idx < 8U; idx++) {
crc = (crc << 1U);
inByte = (inByte << 1U);
if (((crc ^ inByte) & bitMask) != 0U) {
crc = crc ^ poly;
}
}
return ((uint16_t)crc);
}
void crc16Table256Gen(void) {
uint32_t idx;
for (idx = 0; idx < 256U; idx++) {
crcTable[idx] = calcByteCrc16Bitwise(idx << 8U, 0);
}
}
void crc16_init(void) {
int32_t idx;
crc16Table256Gen();
for (idx = 0; idx < N_FAST_FORWARD_TABLES; idx++) {
two_reg_crc16FastForwardTableGen(&ffwTables[idx * N_FAST_FORWARD_TABLE_ENTRIES], ffwLutSteps[idx]);
}
}
unsigned char buff[256] = {
0xB6,0x49,0xB6,0x93,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
};
int main(int argc, char **argv) {
crc16_init();
addCRC(0, 256, buff);
printf("CRC bytes [%x] [%x]", buff[254], buff[255]);
return 0;
}
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C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.
When ever you want to perform a set of operations based on a condition if-else is used.
if(conditional-expression) {
// code
} else {
// code
}
You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.
Switch is an alternative to if-else-if ladder.
switch(conditional-expression) {
case value1:
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break; // optional
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break; // optional
...
default:
// code to be executed when all the above cases are not matched;
}
For loop is used to iterate a set of statements based on a condition.
for(Initialization; Condition; Increment/decrement){
// code
}
While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.
while(condition) {
// code
}
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data-type array-name[size];
data-type array-name[size][size];
Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.
Two types of functions are present in C
Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,
User defined functions are the ones which are written by the programmer based on the requirement.
return_type function_name(parameters);
function_name (parameters)
return_type function_name(parameters) {
//code
}