sort

Exercise from K&R 5.14-5.17 with the intent of going fully in, with 5.17 defining the start structure.

Details

It is a toy sorting program (newbie project) compared to any serious sort program, but it does handle:

• lexiographic
• dictionary,
• numeric
• case insensitive
• reverse sort,

With individual sorting of upto 255 fields, with the option of setting "global" values, which any field specified without further options will use.

The field handling is naive, without any way to set an offset within the fields.

The comparsion functions are fully dedicated to remove any uneccessary if-tests within the comparision. On the other hand, there is just one set of comparison function that handles both lines and individual fields.

Motivation:

Main motivation is the belief in doing the exerceises  of
K&R as something utterly important if I am to continue
with C-programming, which I will  for a while.

Secondly, I had some ideas/concepts I want to try for
speeding up  the sorting on fields with as little overhead
as possible.

Result

Input is prepared into columns but only for as many fields as necessary, and reassmbled again after sorting.

The cost of sorting on a field, is a quicksort algorithm with two more parameters, and a 3 more assignement instructions in the swap routine, which I count for as a success efficency wise, in comparision with other approaches that involves extracting the fields from within quicksort, where I at best would need two calls to field extraction routine, for two lines, maybe multiple times per line during sorting.

Missing parts:

As it stands and is left, it is still a toy, since I
haven't seen any reason for incorporating:

• Fast io and support for large files: (mmap) for files, and maybe fread for streams.

• A merge sort algorithm for sorting with stability with respect to sorting on multiple fields. As quicksort doesn't really make much sense when adjacent rows should be kept adjacent.

Robustness:

The program as such is fairly robust with regards to input, lines with missing fields for sorting are promptly printed to stderr and rejected from the input to the sorting.