//
//  NSData+CRC16.m
//  LipuWaterPurifier
//
//  Created by leon on 2017/3/6.
//  Copyright © 2017年 Lipu. All rights reserved.
//

#import "NSData+CRC16.h"

#define CRC_16 0x8005

@implementation NSData (CRC16)

#define PLOY 0X1021

uint16_t gen_crc16_ccitt(const uint8_t *data, uint16_t size) {
    uint16_t crc = 0;
    uint8_t i;
    for (; size > 0; size--) {
        crc = crc ^ (*data++ <<8);
        for (i = 0; i < 8; i++) {
            if (crc & 0X8000) {
                crc = (crc << 1) ^ PLOY;
            }else {
                crc <<= 1;
            }
        }
        crc &= 0XFFFF;
    }
    return crc;
}

 uint16_t xmodem_crc16_ccitt(const uint8_t *pbBuf, uint32_t dwLen)
{
    uint16_t wCRC = 0;
    uint16_t  bCycle;
    
    while (dwLen-- > 0)
    {
        wCRC ^= (unsigned short) *pbBuf++ << 8;
        for (bCycle = 0; bCycle < 8; bCycle++)
        {
            if (wCRC & 0x8000)
            {
                wCRC = wCRC << 1 ^ 0x1021;
            }
            else
            {
                wCRC <<= 1;
            }
        }
    }
    return wCRC;
}


- (unsigned short)crc16Checksum2
{
    const uint8_t *bytes = (const uint8_t *)[self bytes];
    uint16_t length = (uint16_t)[self length];
    
    return (unsigned short)gen_crc16_ccitt(bytes, length);
}

- (unsigned short)crc16Checksum
{
    const uint8_t *bytes = (const uint8_t *)[self bytes];
    uint16_t length = (uint16_t)[self length];
    return (unsigned short)gen_crc16(bytes, length);
}

uint16_t gen_crc16(const uint8_t *data, uint16_t size)
{
    uint16_t out = 0;
    int bits_read = 0, bit_flag;
    
    /* Sanity check: */
    if(data == NULL)
        return 0;
    
    while(size > 0)
    {
        bit_flag = out >> 15;
        
        /* Get next bit: */
        out <<= 1;
        out |= (*data >> bits_read) & 1; // item a) work from the least significant bits
        
        /* Increment bit counter: */
        bits_read++;
        if(bits_read > 7)
        {
            bits_read = 0;
            data++;
            size--;
        }
        
        /* Cycle check: */
        if(bit_flag)
            out ^= CRC_16;
        
    }
    
    // item b) "push out" the last 16 bits
    int i;
    for (i = 0; i < 16; ++i) {
        bit_flag = out >> 15;
        out <<= 1;
        if(bit_flag)
            out ^= CRC_16;
    }
    
    // item c) reverse the bits
    uint16_t crc = 0;
    i = 0x8000;
    int j = 0x0001;
    for (; i != 0; i >>=1, j <<= 1) {
        if (i & out) crc |= j;
    }
    
    return crc;
}

//十六进制转ASCII
- (NSString *)yx_bluetoothString {
    Byte *byte = (Byte *)self.bytes;
    NSMutableString *s = [NSMutableString new];
    for (NSInteger i = 0; i < self.length; i++) {
        [s appendFormat:@"%c",byte[i]];
    }
    return s;
}

@end