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The Git project is not exactly the easiest project to get started in: it's written in C and POSIX shell, with bits of Perl, Rust and other languages sprinkled into it. On top of that, the project has grown somewhat organically over time, making the codebase hard to navigate. These are problems that we're aware of, and there have been and still are efforts to clean up some of the technical debt that is natural to exist an a project that is more than 20 years old. Furthermore, we provide resources to newcomers that help them out like our coding guidelines, code of conduct or "MyFirstContribution.adoc". But there is a rather practical problem: finding your way around in our project's tree is not easy. Doing a directory listing in the top-level directory will present you with more than 550 files, which makes it extremely hard for a newcomer to figure out what files they are even supposed to look at. This makes the onboarding experience somewhat harder than it really needs to be. This isn't only a problem for newcomers though, as I myself struggle to find the files I am looking for because of the sheer number of files. Besides the problem of discoverability it also creates a problem of structure. It is not obvious at all which files are part of "libgit.a" and which files are only linked into our final executables. So while we have this split in our build systems, that split is not evident at all in our tree. Introduce a new "lib/" directory and move all of our sources for "libgit.a" into it to fix these issues. It makes the split we have evident and reduces the number of files in our top-level tree from 550 files to ~80 files. This is still a lot of files, but it's significantly easier to navigate already. Furthermore, we can further iterate after this step and think about introducing a better structure for remaining files, as well. Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>
87 lines
2.5 KiB
C
87 lines
2.5 KiB
C
#include "git-compat-util.h"
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#include "levenshtein.h"
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/*
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* This function implements the Damerau-Levenshtein algorithm to
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* calculate a distance between strings.
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*
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* Basically, it says how many letters need to be swapped, substituted,
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* deleted from, or added to string1, at least, to get string2.
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*
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* The idea is to build a distance matrix for the substrings of both
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* strings. To avoid a large space complexity, only the last three rows
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* are kept in memory (if swaps had the same or higher cost as one deletion
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* plus one insertion, only two rows would be needed).
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*
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* At any stage, "i + 1" denotes the length of the current substring of
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* string1 that the distance is calculated for.
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*
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* row2 holds the current row, row1 the previous row (i.e. for the substring
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* of string1 of length "i"), and row0 the row before that.
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*
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* In other words, at the start of the big loop, row2[j + 1] contains the
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* Damerau-Levenshtein distance between the substring of string1 of length
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* "i" and the substring of string2 of length "j + 1".
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*
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* All the big loop does is determine the partial minimum-cost paths.
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*
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* It does so by calculating the costs of the path ending in characters
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* i (in string1) and j (in string2), respectively, given that the last
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* operation is a substitution, a swap, a deletion, or an insertion.
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*
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* This implementation allows the costs to be weighted:
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*
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* - w (as in "sWap")
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* - s (as in "Substitution")
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* - a (for insertion, AKA "Add")
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* - d (as in "Deletion")
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*
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* Note that this algorithm calculates a distance _iff_ d == a.
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*/
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int levenshtein(const char *string1, const char *string2,
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int w, int s, int a, int d)
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{
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int len1 = strlen(string1), len2 = strlen(string2);
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int *row0, *row1, *row2;
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int i, j;
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ALLOC_ARRAY(row0, len2 + 1);
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ALLOC_ARRAY(row1, len2 + 1);
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ALLOC_ARRAY(row2, len2 + 1);
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for (j = 0; j <= len2; j++)
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row1[j] = j * a;
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for (i = 0; i < len1; i++) {
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int *dummy;
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row2[0] = (i + 1) * d;
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for (j = 0; j < len2; j++) {
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/* substitution */
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row2[j + 1] = row1[j] + s * (string1[i] != string2[j]);
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/* swap */
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if (i > 0 && j > 0 && string1[i - 1] == string2[j] &&
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string1[i] == string2[j - 1] &&
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row2[j + 1] > row0[j - 1] + w)
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row2[j + 1] = row0[j - 1] + w;
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/* deletion */
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if (row2[j + 1] > row1[j + 1] + d)
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row2[j + 1] = row1[j + 1] + d;
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/* insertion */
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if (row2[j + 1] > row2[j] + a)
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row2[j + 1] = row2[j] + a;
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}
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dummy = row0;
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row0 = row1;
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row1 = row2;
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row2 = dummy;
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}
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i = row1[len2];
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free(row0);
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free(row1);
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free(row2);
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return i;
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}
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