checksum code in C language doesn't work well

[JuQiang]

should be add :

if checksum <0 ch = data[i]+1 # add this line checksum = checksum<<1 + che

[hashborgir]

if (uVar < 0) byte++;
uVar = byte + uVar * 2;

or you can left shift once, inclusive OR with shift right 31 bits + byte

uSum = ((uSum << 1) | (uSum >> 31)) + (unsigned)saveFileData[i];