計算c字元的長度，保證不超過2^30，c字元

計算c字元的長度，保證不超過2^30，c字元

來自sqlite3源碼

/*** Compute a string length that is limited to what can be stored in** lower 30 bits of a 32-bit signed integer.**** The value returned will never be negative.  Nor will it ever be greater** than the actual length of the string.  For very long strings (greater** than 1GiB) the value returned might be less than the true string length.*/int sqlite3Strlen30(const char *z){  if( z==0 ) return 0;  return 0x3fffffff & (int)strlen(z);}