This is not a home assignment! We have a binary data file which has following data structure: (It is a 12 byte structure): I need to find out Epoch time value(total time value is packed in 42 bits as described below): Field-1 : Byte 1, Byte 2, + 6 Bits from Byte 3 Time-1 : 2 Bits from Byte 3 + Byte 4 Time-2 : Byte 5, Byte 6, Byte 7, Byte 8 Field-2 : Byte 9, Byte 10, Byte 11, Byte 12 For Field-1 and Field-2 I do not have issue as they can be taken out easily. I need time value in Epoch Time (long) as it has been packed in Bytes 5,6,7,8 and 3 and 4 as follows: (the bit structure for the time value is as follows): Bytes 5 to 8 (32 bit word) Packs time value bits from 0 thru 31 (byte 5 has 0 to 7 bits, byte 6 has 8 to 15, byte 7 has 16 to 23, byte 8 has 24 to 31). the remaining 10 bits of time value are packed in Bytes 3 and byte 4 as follows: byte 3 has 2 bits:32 and 33, and Byte 4 has remaining bits : 34 to 41. So total bits for time value is 42 bits, packed as above. I need to compute epoch value coming out of these 42 bits. How do I do it? I have done something like this but not sure it gives me correct value: typedef struct P_HEADER { unsigned int tmuNumber : 21; unsigned int time1 : 10; // Bits 6,7 from Byte-3 + 8 bits from Byte-4 unsigned int time2 : 32; // 32 bits: Bytes 5,6,7,8 unsigned int traceKey : 32; } __attribute__((__packed__)) P_HEADER; Then in the code : P_HEADER *header1; //get input string in hexa,etc..etc.. //parse the input with the header as : header1 = (P_HEADER *)inputBuf; // then print the header1->time1, header1->time2 .... long ttime = header1->time1|header1->time2; //?? is this the way to get values out? Any hint tip will be appreciated. Environment is : gcc 4.1, Linux Thanks in advance.