unleashed-firmware/lib/nfc/helpers/nfc_util.c

#include "nfc_util.h"

#include <furi.h>

static const uint8_t nfc_util_odd_byte_parity[256] = {
    1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0,
    1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1,
    1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 1, 1,
    0, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0,
    1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 1,
    0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0,
    0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1,
    0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
    1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1};

uint8_t nfc_util_even_parity32(uint32_t data) {
    // data ^= data >> 16;
    // data ^= data >> 8;
    // return !nfc_util_odd_byte_parity[data];
    return (__builtin_parity(data) & 0xFF);
}

uint8_t nfc_util_odd_parity8(uint8_t data) {
    return nfc_util_odd_byte_parity[data];
}

void nfc_util_odd_parity(const uint8_t* src, uint8_t* dst, uint8_t len) {
    furi_check(src);
    furi_check(dst);

    uint8_t parity = 0;
    uint8_t bit = 0;
    while(len--) {
        parity |= nfc_util_odd_parity8(*src) << (7 - bit); // parity is MSB first
        bit++;
        if(bit == 8) {
            *dst = parity;
            dst++;
            parity = 0;
            bit = 0;
        }
        src++;
    }

    if(bit) {
        *dst = parity;
    }
}