麻烦大家帮忙解释一下有些不懂的地方

#define TEA_ROUNDS 0x20 定义循环32轮
#define TEA_DELTA 0x9E3779B9 下面这两个变量做什么啊
#define TEA_SUM 0xE3779B90

void tiny_encrypt(unsigned long *const v, unsigned long *const w,
const unsigned long *const k)
{
register unsigned long
y = v[0],
z = v[1],
a = k[0],
b = k[1],
c = k[2],
d = k[3],  这些赋值看不懂，为什么把这些数组赋值给a b c……
n = TEA_ROUNDS,
sum = 0,
delta = TEA_DELTA;

while (n-- > 0) {
sum += delta;
y += (z << 4) + a ^ z + sum ^ (z >> 5) + b;
z += (y << 4) + c ^ y + sum ^ (y >> 5) + d;
}  循环32轮，这里面做什么啊
w[0] = y;
w[1] = z;
}

还有一个版本，和上面那个大同小异

void EncMusic(PDWORD pData, PDWORD pEncData)
{
  DWORD  Key1=  0x45AD9059;
  
  DWORD  FKey1= 0xF03E934F;
  DWORD  FKey2= 0x27BDB886;
  DWORD  LKey1= 0xD0AAE945;
  DWORD  LKey2= 0x993BA3AE;
  DWORD FirstData,LastData,Count,Key;  
  
  Count=32;
  Key=0;
  FirstData = *pData;
  LastData = *(pData+1);
  
  do
  {  
    Key= Key+Key1;
    FirstData=FirstData+ ((FKey2+(LastData<<4)) ^ (FKey1+ (LastData>>5)) ^ (Key+LastData));
    LastData=LastData+((LKey2 +(FirstData<<4)) ^ (LKey1+ (FirstData>>5)) ^ (Key+FirstData));
    Count--;
  }while(Count!=0);
  *pEncData = FirstData;
  *(pEncData+1) = LastData;
}

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