128-bit structure or 2 64-bit records for performance and readability

Question

I am sorting 128-bit entries in a large file (10 with GB). The algorithm works fine and currently uses uint64_t , and two of them are equal to the same record. This is on a modern 64-bit system.

In the interest of code readability, it is interesting to know whether it is possible to create a structure of type typedef struct u128t {uint64_t hi, uint64_t} u128t instead of two 64-bit records. This will do an array index cleanup and assignment, but I will have to implement a comparator function.

Is this a portable solution and should I expect it to work at the same speed as the original implementation?

Further reading:

• http://gcc.gnu.org/onlinedocs/gcc/_005f_005fint128.html - for 128-bit systems
• http://en.wikipedia.org/wiki/C_data_types - c types
• Copy structure to structure in C - copy structures

Answer 1

Using the structure is fine.

I would do something like this:

 #if COMPILER_WHICH_SUPPORTS_128_BIT_TYPE typedef __uint128 u128t; #define COMPARE(a, b) ((a) == (b)) #else typedef struct { uint64_t hi; uint64_t lo; } u128t; #define COMPARE(a, b) MyCompareFunction((a), (b)) #endif