helpers.c

来自「Pic Nic 16f877/18f452控制 rtl8019as 原代码」· C语言 代码 · 共 48 行

/*
 * helpers.c
 *
 * Some basic functions to help others
 *
 */

//Swap MSByte and LSByte of a 16-Bit Word
WORD_VAL swap16(int16 v) {
    WORD_VAL t;
    int8 b;

    t = v;
    b = t.MSB;
    t.MSB = t.LSB;
    t.LSB = b;

    return t;
}

//Swap MSByte and LSByte of a 32-BitD ouble Word
DWORD_VAL swap32(int32 v) {
    int8 b;
    DWORD_VAL myV;

    myV = v;
    b = myV.HIMSB;
    myV.HIMSB = myV.LOLSB;
    myV.LOLSB = b;
    b = myV.HILSB;
    myV.HILSB = myV.LOMSB;
    myV.LOMSB = b;

    return myV;
}

//Compute checksum
//This function is called several times and keeps track of checksum on chksum var
void calc_chksum(long int data) {
  long int prev_chksum;

  prev_chksum = chksum;   // Keep a copy of the current checksum
  chksum += data;

  if (chksum < prev_chksum)
   chksum ++;
}