Mercurial > gnulib
changeset 29234:0eb7646858e6
Add more comments about Knuth-Morris-Pratt algorithm.
| author | Bruno Haible <bruno@clisp.org> |
|---|---|
| date | Wed, 26 Dec 2007 16:10:15 +0100 |
| parents | 6ae668043e37 |
| children | dcfae8124cd4 |
| files | ChangeLog lib/c-strcasestr.c lib/c-strstr.c lib/mbscasestr.c lib/mbsstr.c lib/memmem.c lib/strcasestr.c |
| diffstat | 7 files changed, 299 insertions(+), 26 deletions(-) [+] |
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--- a/ChangeLog Wed Dec 26 16:02:46 2007 +0100 +++ b/ChangeLog Wed Dec 26 16:10:15 2007 +0100 @@ -1,3 +1,12 @@ +2007-12-23 Bruno Haible <bruno@clisp.org> + + * lib/c-strcasestr.c: Add more comments. + * lib/c-strstr.c: Likewise. + * lib/mbscasestr.c: Likewise. + * lib/mbsstr.c: Likewise. + * lib/strcasestr.c: Likewise. + * lib/memmem.c: Likewise. + 2007-12-23 Bruno Haible <bruno@clisp.org> * tests/test-memmem.c: Include <string.h> first.
--- a/lib/c-strcasestr.c Wed Dec 26 16:02:46 2007 +0100 +++ b/lib/c-strcasestr.c Wed Dec 26 16:10:15 2007 +0100 @@ -43,34 +43,67 @@ /* Fill the table. For 0 < i < m: 0 < table[i] <= i is defined such that - rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i] - implies - forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1], + forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x], and table[i] is as large as possible with this property. + This implies: + 1) For 0 < i < m: + If table[i] < i, + needle[table[i]..i-1] = needle[0..i-1-table[i]]. + 2) For 0 < i < m: + rhaystack[0..i-1] == needle[0..i-1] + and exists h, i <= h < m: rhaystack[h] != needle[h] + implies + forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1]. table[0] remains uninitialized. */ { size_t i, j; + /* i = 1: Nothing to verify for x = 0. */ table[1] = 1; j = 0; + for (i = 2; i < m; i++) { + /* Here: j = i-1 - table[i-1]. + The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold + for x < table[i-1], by induction. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ unsigned char b = c_tolower ((unsigned char) needle[i - 1]); for (;;) { + /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x] + is known to hold for x < i-1-j. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ if (b == c_tolower ((unsigned char) needle[j])) { + /* Set table[i] := i-1-j. */ table[i] = i - ++j; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for x = i-1-j, because + needle[i-1] != needle[j] = needle[i-1-x]. */ if (j == 0) { + /* The inequality holds for all possible x. */ table[i] = i; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for i-1-j < x < i-1-j+table[j], because for these x: + needle[x..i-2] + = needle[x-(i-1-j)..j-1] + != needle[0..j-1-(x-(i-1-j))] (by definition of table[j]) + = needle[0..i-2-x], + hence needle[x..i-1] != needle[0..i-1-x]. + Furthermore + needle[i-1-j+table[j]..i-2] + = needle[table[j]..j-1] + = needle[0..j-1-table[j]] (by definition of table[j]). */ j = j - table[j]; } + /* Here: j = i - table[i]. */ } }
--- a/lib/c-strstr.c Wed Dec 26 16:02:46 2007 +0100 +++ b/lib/c-strstr.c Wed Dec 26 16:10:15 2007 +0100 @@ -42,34 +42,67 @@ /* Fill the table. For 0 < i < m: 0 < table[i] <= i is defined such that - rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i] - implies - forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1], + forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x], and table[i] is as large as possible with this property. + This implies: + 1) For 0 < i < m: + If table[i] < i, + needle[table[i]..i-1] = needle[0..i-1-table[i]]. + 2) For 0 < i < m: + rhaystack[0..i-1] == needle[0..i-1] + and exists h, i <= h < m: rhaystack[h] != needle[h] + implies + forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1]. table[0] remains uninitialized. */ { size_t i, j; + /* i = 1: Nothing to verify for x = 0. */ table[1] = 1; j = 0; + for (i = 2; i < m; i++) { + /* Here: j = i-1 - table[i-1]. + The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold + for x < table[i-1], by induction. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ unsigned char b = (unsigned char) needle[i - 1]; for (;;) { + /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x] + is known to hold for x < i-1-j. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ if (b == (unsigned char) needle[j]) { + /* Set table[i] := i-1-j. */ table[i] = i - ++j; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for x = i-1-j, because + needle[i-1] != needle[j] = needle[i-1-x]. */ if (j == 0) { + /* The inequality holds for all possible x. */ table[i] = i; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for i-1-j < x < i-1-j+table[j], because for these x: + needle[x..i-2] + = needle[x-(i-1-j)..j-1] + != needle[0..j-1-(x-(i-1-j))] (by definition of table[j]) + = needle[0..i-2-x], + hence needle[x..i-1] != needle[0..i-1-x]. + Furthermore + needle[i-1-j+table[j]..i-2] + = needle[table[j]..j-1] + = needle[0..j-1-table[j]] (by definition of table[j]). */ j = j - table[j]; } + /* Here: j = i - table[i]. */ } }
--- a/lib/mbscasestr.c Wed Dec 26 16:02:46 2007 +0100 +++ b/lib/mbscasestr.c Wed Dec 26 16:10:15 2007 +0100 @@ -48,34 +48,67 @@ /* Fill the table. For 0 < i < m: 0 < table[i] <= i is defined such that - rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i] - implies - forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1], + forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x], and table[i] is as large as possible with this property. + This implies: + 1) For 0 < i < m: + If table[i] < i, + needle[table[i]..i-1] = needle[0..i-1-table[i]]. + 2) For 0 < i < m: + rhaystack[0..i-1] == needle[0..i-1] + and exists h, i <= h < m: rhaystack[h] != needle[h] + implies + forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1]. table[0] remains uninitialized. */ { size_t i, j; + /* i = 1: Nothing to verify for x = 0. */ table[1] = 1; j = 0; + for (i = 2; i < m; i++) { + /* Here: j = i-1 - table[i-1]. + The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold + for x < table[i-1], by induction. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ unsigned char b = TOLOWER ((unsigned char) needle[i - 1]); for (;;) { + /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x] + is known to hold for x < i-1-j. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ if (b == TOLOWER ((unsigned char) needle[j])) { + /* Set table[i] := i-1-j. */ table[i] = i - ++j; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for x = i-1-j, because + needle[i-1] != needle[j] = needle[i-1-x]. */ if (j == 0) { + /* The inequality holds for all possible x. */ table[i] = i; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for i-1-j < x < i-1-j+table[j], because for these x: + needle[x..i-2] + = needle[x-(i-1-j)..j-1] + != needle[0..j-1-(x-(i-1-j))] (by definition of table[j]) + = needle[0..i-2-x], + hence needle[x..i-1] != needle[0..i-1-x]. + Furthermore + needle[i-1-j+table[j]..i-2] + = needle[table[j]..j-1] + = needle[0..j-1-table[j]] (by definition of table[j]). */ j = j - table[j]; } + /* Here: j = i - table[i]. */ } } @@ -154,34 +187,67 @@ /* Fill the table. For 0 < i < m: 0 < table[i] <= i is defined such that - rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i] - implies - forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1], + forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x], and table[i] is as large as possible with this property. + This implies: + 1) For 0 < i < m: + If table[i] < i, + needle[table[i]..i-1] = needle[0..i-1-table[i]]. + 2) For 0 < i < m: + rhaystack[0..i-1] == needle[0..i-1] + and exists h, i <= h < m: rhaystack[h] != needle[h] + implies + forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1]. table[0] remains uninitialized. */ { size_t i, j; + /* i = 1: Nothing to verify for x = 0. */ table[1] = 1; j = 0; + for (i = 2; i < m; i++) { + /* Here: j = i-1 - table[i-1]. + The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold + for x < table[i-1], by induction. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ mbchar_t *b = &needle_mbchars[i - 1]; for (;;) { + /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x] + is known to hold for x < i-1-j. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ if (mb_equal (*b, needle_mbchars[j])) { + /* Set table[i] := i-1-j. */ table[i] = i - ++j; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for x = i-1-j, because + needle[i-1] != needle[j] = needle[i-1-x]. */ if (j == 0) { + /* The inequality holds for all possible x. */ table[i] = i; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for i-1-j < x < i-1-j+table[j], because for these x: + needle[x..i-2] + = needle[x-(i-1-j)..j-1] + != needle[0..j-1-(x-(i-1-j))] (by definition of table[j]) + = needle[0..i-2-x], + hence needle[x..i-1] != needle[0..i-1-x]. + Furthermore + needle[i-1-j+table[j]..i-2] + = needle[table[j]..j-1] + = needle[0..j-1-table[j]] (by definition of table[j]). */ j = j - table[j]; } + /* Here: j = i - table[i]. */ } }
--- a/lib/mbsstr.c Wed Dec 26 16:02:46 2007 +0100 +++ b/lib/mbsstr.c Wed Dec 26 16:10:15 2007 +0100 @@ -45,34 +45,67 @@ /* Fill the table. For 0 < i < m: 0 < table[i] <= i is defined such that - rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i] - implies - forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1], + forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x], and table[i] is as large as possible with this property. + This implies: + 1) For 0 < i < m: + If table[i] < i, + needle[table[i]..i-1] = needle[0..i-1-table[i]]. + 2) For 0 < i < m: + rhaystack[0..i-1] == needle[0..i-1] + and exists h, i <= h < m: rhaystack[h] != needle[h] + implies + forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1]. table[0] remains uninitialized. */ { size_t i, j; + /* i = 1: Nothing to verify for x = 0. */ table[1] = 1; j = 0; + for (i = 2; i < m; i++) { + /* Here: j = i-1 - table[i-1]. + The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold + for x < table[i-1], by induction. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ unsigned char b = (unsigned char) needle[i - 1]; for (;;) { + /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x] + is known to hold for x < i-1-j. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ if (b == (unsigned char) needle[j]) { + /* Set table[i] := i-1-j. */ table[i] = i - ++j; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for x = i-1-j, because + needle[i-1] != needle[j] = needle[i-1-x]. */ if (j == 0) { + /* The inequality holds for all possible x. */ table[i] = i; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for i-1-j < x < i-1-j+table[j], because for these x: + needle[x..i-2] + = needle[x-(i-1-j)..j-1] + != needle[0..j-1-(x-(i-1-j))] (by definition of table[j]) + = needle[0..i-2-x], + hence needle[x..i-1] != needle[0..i-1-x]. + Furthermore + needle[i-1-j+table[j]..i-2] + = needle[table[j]..j-1] + = needle[0..j-1-table[j]] (by definition of table[j]). */ j = j - table[j]; } + /* Here: j = i - table[i]. */ } } @@ -146,34 +179,67 @@ /* Fill the table. For 0 < i < m: 0 < table[i] <= i is defined such that - rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i] - implies - forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1], + forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x], and table[i] is as large as possible with this property. + This implies: + 1) For 0 < i < m: + If table[i] < i, + needle[table[i]..i-1] = needle[0..i-1-table[i]]. + 2) For 0 < i < m: + rhaystack[0..i-1] == needle[0..i-1] + and exists h, i <= h < m: rhaystack[h] != needle[h] + implies + forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1]. table[0] remains uninitialized. */ { size_t i, j; + /* i = 1: Nothing to verify for x = 0. */ table[1] = 1; j = 0; + for (i = 2; i < m; i++) { + /* Here: j = i-1 - table[i-1]. + The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold + for x < table[i-1], by induction. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ mbchar_t *b = &needle_mbchars[i - 1]; for (;;) { + /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x] + is known to hold for x < i-1-j. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ if (mb_equal (*b, needle_mbchars[j])) { + /* Set table[i] := i-1-j. */ table[i] = i - ++j; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for x = i-1-j, because + needle[i-1] != needle[j] = needle[i-1-x]. */ if (j == 0) { + /* The inequality holds for all possible x. */ table[i] = i; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for i-1-j < x < i-1-j+table[j], because for these x: + needle[x..i-2] + = needle[x-(i-1-j)..j-1] + != needle[0..j-1-(x-(i-1-j))] (by definition of table[j]) + = needle[0..i-2-x], + hence needle[x..i-1] != needle[0..i-1-x]. + Furthermore + needle[i-1-j+table[j]..i-2] + = needle[table[j]..j-1] + = needle[0..j-1-table[j]] (by definition of table[j]). */ j = j - table[j]; } + /* Here: j = i - table[i]. */ } }
--- a/lib/memmem.c Wed Dec 26 16:02:46 2007 +0100 +++ b/lib/memmem.c Wed Dec 26 16:10:15 2007 +0100 @@ -45,34 +45,67 @@ /* Fill the table. For 0 < i < m: 0 < table[i] <= i is defined such that - rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i] - implies - forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1], + forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x], and table[i] is as large as possible with this property. + This implies: + 1) For 0 < i < m: + If table[i] < i, + needle[table[i]..i-1] = needle[0..i-1-table[i]]. + 2) For 0 < i < m: + rhaystack[0..i-1] == needle[0..i-1] + and exists h, i <= h < m: rhaystack[h] != needle[h] + implies + forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1]. table[0] remains uninitialized. */ { size_t i, j; + /* i = 1: Nothing to verify for x = 0. */ table[1] = 1; j = 0; + for (i = 2; i < m; i++) { + /* Here: j = i-1 - table[i-1]. + The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold + for x < table[i-1], by induction. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ unsigned char b = (unsigned char) needle[i - 1]; for (;;) { + /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x] + is known to hold for x < i-1-j. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ if (b == (unsigned char) needle[j]) { + /* Set table[i] := i-1-j. */ table[i] = i - ++j; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for x = i-1-j, because + needle[i-1] != needle[j] = needle[i-1-x]. */ if (j == 0) { + /* The inequality holds for all possible x. */ table[i] = i; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for i-1-j < x < i-1-j+table[j], because for these x: + needle[x..i-2] + = needle[x-(i-1-j)..j-1] + != needle[0..j-1-(x-(i-1-j))] (by definition of table[j]) + = needle[0..i-2-x], + hence needle[x..i-1] != needle[0..i-1-x]. + Furthermore + needle[i-1-j+table[j]..i-2] + = needle[table[j]..j-1] + = needle[0..j-1-table[j]] (by definition of table[j]). */ j = j - table[j]; } + /* Here: j = i - table[i]. */ } } @@ -164,7 +197,7 @@ size_t comparison_count = 0; /* Speed up the following searches of needle by caching its first - character. */ + byte. */ char b = *Needle++; for (;; Haystack++) @@ -195,7 +228,7 @@ outer_loop_count++; comparison_count++; if (*Haystack == b) - /* The first character matches. */ + /* The first byte matches. */ { const char *rhaystack = Haystack + 1; const char *rneedle = Needle;
--- a/lib/strcasestr.c Wed Dec 26 16:02:46 2007 +0100 +++ b/lib/strcasestr.c Wed Dec 26 16:10:15 2007 +0100 @@ -45,34 +45,67 @@ /* Fill the table. For 0 < i < m: 0 < table[i] <= i is defined such that - rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i] - implies - forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1], + forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x], and table[i] is as large as possible with this property. + This implies: + 1) For 0 < i < m: + If table[i] < i, + needle[table[i]..i-1] = needle[0..i-1-table[i]]. + 2) For 0 < i < m: + rhaystack[0..i-1] == needle[0..i-1] + and exists h, i <= h < m: rhaystack[h] != needle[h] + implies + forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1]. table[0] remains uninitialized. */ { size_t i, j; + /* i = 1: Nothing to verify for x = 0. */ table[1] = 1; j = 0; + for (i = 2; i < m; i++) { + /* Here: j = i-1 - table[i-1]. + The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold + for x < table[i-1], by induction. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ unsigned char b = TOLOWER ((unsigned char) needle[i - 1]); for (;;) { + /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x] + is known to hold for x < i-1-j. + Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ if (b == TOLOWER ((unsigned char) needle[j])) { + /* Set table[i] := i-1-j. */ table[i] = i - ++j; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for x = i-1-j, because + needle[i-1] != needle[j] = needle[i-1-x]. */ if (j == 0) { + /* The inequality holds for all possible x. */ table[i] = i; break; } + /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds + for i-1-j < x < i-1-j+table[j], because for these x: + needle[x..i-2] + = needle[x-(i-1-j)..j-1] + != needle[0..j-1-(x-(i-1-j))] (by definition of table[j]) + = needle[0..i-2-x], + hence needle[x..i-1] != needle[0..i-1-x]. + Furthermore + needle[i-1-j+table[j]..i-2] + = needle[table[j]..j-1] + = needle[0..j-1-table[j]] (by definition of table[j]). */ j = j - table[j]; } + /* Here: j = i - table[i]. */ } }