/*
 * crc.c
 *
 *  Created on: 7 ìàð. 2024 ã.
 *      Author: seklyuts
 */

#include "f28x_project.h"


const int order = 6;
const unsigned long polynom = 0x43;
const int direct = 1;
const unsigned long crcinit = 0x0000;
const unsigned long crcxor = 0xffff;
const int refin = 0;
const int refout = 0;
// internal global values:
unsigned long crcmask;
unsigned long crchighbit;
unsigned long crcinit_direct;
unsigned long crcinit_nondirect;
unsigned long crctab[256];


unsigned long reflect (unsigned long crc, int bitnum) {
    // reflects the lower ’bitnum’ bits of ’crc’
    unsigned long i, j=1, crcout=0;
    for (i=(unsigned long)1<<(bitnum-1); i; i>>=1) {
        if (crc & i) crcout|=j;
        j<<= 1;
    }
    return (crcout);
}


unsigned long crcbitbybit(unsigned char* p, unsigned long len) {
    // bit by bit algorithm with augmented zero bytes.
    // does not use lookup table, suited for polynom orders between 1...32.
    unsigned long i, j, c, bit;
    unsigned long crc = crcinit_nondirect;
    for (i=0; i<len; i++) {
        c = (unsigned long)*p++;
        if (refin) c = reflect(c, 8);
        for (j=0x80; j; j>>=1) {
            bit = crc & crchighbit;
            crc<<= 1;
            if (c & j) crc|= 1;
            if (bit) crc^= polynom;
        }
    }
    for (i=0; i<order; i++) {
        bit = crc & crchighbit;
        crc<<= 1;
        if (bit) crc^= polynom;
    }
    if (refout) crc=reflect(crc, order);
    crc^= crcxor;
    crc&= crcmask;
    return(crc);
}


//unsigned long crcbitbybitfast(unsigned char* p, unsigned long len) {
uint16_t crcbitbybitfast(uint64_t data)
{
    // fast bit by bit algorithm without augmented zero bytes.
    // does not use lookup table, suited for polynom orders between 1...32.
    unsigned long i, j, c, bit;
    unsigned long crc = crcinit_direct;

    crcmask = ((((uint64_t)1<<(order-1))-1)<<1)|1;
    crchighbit = (uint64_t)1<<(order-1);

    uint16_t p[5];
    p[4] = data & 0xFF;
    p[3] = (data >> 8) & 0xFF;
    p[2] = (data >> 16) & 0xFF;
    p[1] = (data >> 24) & 0xFF;
    p[0] = (data >> 32) & 0xFF;
    for (i=0; i<5; i++) {
        c = p[i];
//        if (refin) c = reflect(c, 8);
        for (j=0x80; j; j>>=1) {
            bit = crc & crchighbit;
            crc<<= 1;
            if (c & j) bit^= crchighbit;
            if (bit) crc^= polynom;
        }
    }
//    if (refout) crc=reflect(crc, order);
    crc^= crcxor;
    crc&= crcmask;
    return(crc);
}


#define ALL_BITS 38
#define CS_BITS 6


uint16_t calcCRC(uint64_t data) // 38 bit -> 6 bit // x6 + x1 + 1/// poly = 0b1000011 = 0x86;
{
    uint64_t temp1, temp2, crc = 0;
    uint64_t poly = (uint64_t)0b1000011 << (ALL_BITS - CS_BITS - 1);
    uint16_t i = 0;
    crc = poly;
    temp1 = data;
    crc ^= temp1;

    for(i=0; i < (ALL_BITS - CS_BITS); i++)
    {
//        crc = (crc & ((uint64_t)1 << (ALL_BITS-1))) ? ((crc ^ poly) << 1) : (crc << 1);

        temp2 = ((uint64_t)1 << (ALL_BITS-1));

        if(crc & temp2)
        {
            crc = ((crc ^ poly) << 1);
        }
        else
        {
            crc =  (crc << 1);
        }

    }
    return (crc >> (ALL_BITS - CS_BITS));
}