Прошу помочь записать следующую функцию так, чтобы порядок следования операций был однозначно ясен. По сути, расставить правильно скобочки. А лучше переписать в несколько строк, но с однозначным исходом операций.
/// Возвращение посчитанного значения crc16
unsigned short int crc16(unsigned char *C, unsigned long int size, unsigned short int Crc)
{
unsigned long int acc = Crc;
while(size--)
acc = (acc >> 8) ^ crc_table_16[(acc ^* C++) & 0x00FF];
return (unsigned short int)acc;
}
О, вот сложение по модулю 2 я знаю! Спасибо
(acc ^* C++) & 0x00FF
Да. Поразрядное выполнение операции И над результатом предыдущих операций и числа 255.
/**************************************************************************
*========================== ЗАО "ННН" ====================================*
***************************************************************************
*
* Заголовок: Функции вычисления контрольных сумм CRC16
* Имя файла: CRC16.h
*
*
* Компилятор: WinAVR 2006(avr-gcc (GCC) 3.4.6)
* Дата начала: 20.09.2007
* Последнее обновление: 05.09.2007
* Автор: Литкевич Юрий Иванович
* Support E-mail:
*
* Описание: Вычисление CRC16
* полином: X^16+X^14+X^1 (вроде бы :)
*
*
* Log:
*
*
*
****************************************************************************/
#ifndef CRC16_H
#define CRC16_H
/*************************** FuncProto *************************************/
#ifdef __cplusplus
extern "C" {
#endif
//! calculate CRC16 (X^16+X^14+X^1) of buffer *data lenth datacnt
extern unsigned int CalcCRC16(unsigned char *data, int datacnt);
#ifdef __cplusplus
}
#endif
#endif /* CRC16_H */
/**************************************************************************
*========================== ЗАО "ННН" ====================================*
***************************************************************************
*
* Заголовок: Функции вычисления контрольных сумм CRC16
* Имя файла: CRC16.с
*
*
* Компилятор: WinAVR 2006(avr-gcc (GCC) 3.4.6)
* Дата начала: 20.09.2007
* Последнее обновление: 05.09.2007
* Автор: Литкевич Юрий Иванович
* Support E-mail: lit-uriy@yandex.ru
*
* Описание: Вычисление CRC16
* полином: X^16+X^14+X^1 (вроде бы :)
*
*
* Log:
*
*
*
****************************************************************************/
#include "crc16.h"
/* Table of CRC values for hi-order byte */
const char auchCRCHi[] =
{
0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41, 0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40,
0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40, 0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41,
0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40, 0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41,
0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41, 0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40,
0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40, 0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41,
0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41, 0x01,0xC0,0x80,0x22, 0x00,0xC1,0x81,0x40,
0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41, 0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40,
0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40, 0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41,
0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40, 0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80, 0x41,
0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41, 0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40,
0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41, 0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40,
0x01,0xC0,0x80,0x41, 0x00,0xC1, 0x81,0x40, 0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41,
0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41, 0x00,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40,
0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40, 0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41,
0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40, 0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41,
0x00,0xC1,0x81,0x40, 0x01,0xC0,0x80,0x41, 0x01,0xC0,0x80,0x41, 0x00,0xC1,0x81,0x40
};
/* Table of CRC values for low-order byte */
const char auchCRCLo[] =
{
0x00,0xC0,0xC1,0x01,0xC3,0x03,0x02,0xC2,0xC6,0x06,0x07,0xC7,0x05,
0xC5,0xC4,0x04,0xCC,0x0C,0x0D,0xCD,0x0F,0xCF,0xCE,0x0E,0x0A,0xCA,
0xCB,0x0B,0xC9,0x09,0x08,0xC8,0xD8,0x18,0x19,0xD9,0x1B,0xDB,0xDA,
0x1A,0x1E,0xDE,0xDF,0x1F,0xDD,0x1D,0x1C,0xDC,0x14,0xD4,0xD5,0x15,
0xD7,0x17,0x16,0xD6,0xD2,0x12,0x13,0xD3,0x11,0xD1,0xD0,0x10,0xF0,
0x30,0x31,0xF1,0x33,0xF3,0xF2,0x32,0x36,0xF6,0xF7,0x37,0xF5,0x35,
0x34,0xF4,0x3C,0xFC,0xFD,0x3D,0xFF,0x3F,0x3E,0xFE,0xFA,0x3A,0x3B,
0xFB,0x39,0xF9,0xF8,0x38,0x28,0xE8,0xE9,0x29,0xEB,0x2B,0x2A,0xEA,
0xEE,0x2E,0x2F,0xEF,0x2D,0xED,0xEC,0x2C,0xE4,0x24,0x25,0xE5,0x27,
0xE7,0xE6,0x26,0x22,0xE2,0xE3,0x23,0xE1,0x21,0x20,0xE0,0xA0,0x60,
0x61,0xA1,0x63,0xA3,0xA2,0x62,0x66,0xA6,0xA7,0x67,0xA5,0x65,0x64,
0xA4,0x6C,0xAC,0xAD,0x6D,0xAF,0x6F,0x6E,0xAE,0xAA,0x6A,0x6B,0xAB,
0x69,0xA9,0xA8,0x68,0x78,0xB8,0xB9,0x79,0xBB,0x7B,0x7A,0xBA,0xBE,
0x7E,0x7F,0xBF,0x7D,0xBD,0xBC,0x7C,0xB4,0x74,0x75,0xB5,0x77,0xB7,
0xB6,0x76,0x72,0xB2,0xB3,0x73,0xB1,0x71,0x70,0xB0,0x50,0x90,0x91,
0x51,0x93,0x53,0x52,0x92,0x96,0x56,0x57,0x97,0x55,0x95,0x94,0x54,
0x9C,0x5C,0x5D,0x9D,0x5F,0x9F,0x9E,0x5E,0x5A,0x9A,0x9B,0x5B,0x99,
0x59,0x58,0x98,0x88,0x48,0x49,0x89,0x4B,0x8B,0x8A,0x4A,0x4E,0x8E,
0x8F,0x4F,0x8D,0x4D,0x4C,0x8C,0x44,0x84,0x85,0x45,0x87,0x47,0x46,
0x86,0x82,0x42,0x43,0x83,0x41,0x81,0x80,0x40
};
/*******************************************************************************
* Функция вычисления шестнадцатиразрядной
* циклической контрольной суммы CRC-16 буфера data длиной datacnt
*-------------------------------------------------------------------------------
*Входные данные: *data,datacnt
*Выходные данные: crc16
*******************************************************************************/
unsigned int CalcCRC16(unsigned char *data, int datacnt)
{
unsigned char uIndex;
unsigned char uchCRCHi = 0xFF; /* high CRC byte initialized */
unsigned char uchCRCLo = 0xFF; /* low CRC byte initialized */
while (datacnt--) /* pass through message buffer */
{
uIndex = uchCRCHi ^ *data++; /* calculate the CRC */
uchCRCHi = uchCRCLo ^ auchCRCHi[uIndex];
uchCRCLo = auchCRCLo[uIndex];
}
return (uchCRCHi << 8 | uchCRCLo);
}
Да судя по всему та же функция. Вот таблица:
/// Массив значений для вычисления crc16
static unsigned short int crc_table_16[] =
{
0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
};
Мда .... уж. Вопрос решился. Спасибо за помощь.
Дело было в том, что была использована функция memcpy, которая, видимо, где-то тянула мусор, из-за чего crc при вычислении различались!
Форум Invision Power Board (http://www.invisionboard.com)
© Invision Power Services (http://www.invisionpower.com)