@@ -321,9 +321,8 @@ def test_rindex(self):
     def test_find_periodic_pattern(self):
         """Cover the special path for periodic patterns."""
         def reference_find(p, s):
-            m = len(p)
             for i in range(len(s)):
-                if s[i:i+m] == p:
+                if s.startswith(p, i):
                     return i
             return -1
 
@@ -332,8 +331,8 @@ def reference_find(p, s):
         for _ in range(1000):
             p0 = ''.join(choices('abcde', k=rr(10))) * rr(10, 20)
             p = p0[:len(p0) - rr(10)] # pop off some characters
-            left = ''.join(choices('abcdef', k=rr(200)))
-            right = ''.join(choices('abcdef', k=rr(200)))
+            left = ''.join(choices('abcdef', k=rr(2000)))
+            right = ''.join(choices('abcdef', k=rr(2000)))
             text = left + p + right
             with self.subTest(p=p, text=text):
                 self.checkequal(reference_find(p, text),
@@ -344,14 +343,14 @@ def test_find_shift_table_overflow(self):
         N = 2**16 + 100 # Overflow the 16-bit shift table
 
         # first check the periodic case
-        # here, the shift for 'b' is N.
+        # here, the shift for 'b' is N + 1.
         pattern1 = 'a' * N + 'b' + 'a' * N
         text1 = 'babbaa' * N + pattern1
         self.checkequal(len(text1)-len(pattern1),
                         text1, 'find', pattern1)
 
         # now check the non-periodic case
-        # here, the shift for 'd' is 3*(N+1)
+        # here, the shift for 'd' is 3*(N+1)+1
         pattern2 = 'ddd' + 'abc' * N + "eee"
         text2 = pattern2[:-1] + "ddeede" * 2 * N + pattern2 + "de" * N
         self.checkequal(len(text2) - N*len("de") - len(pattern2),
 
@@ -357,7 +357,7 @@ STRINGLIB(_two_way)(const STRINGLIB_CHAR *haystack, Py_ssize_t len_haystack,
             LOG("\n> "); LOG("%*s", window - haystack + i, "");
             LOG(" ^ <-- cut\n");
 
-            if (window[i] != needle[i++]) {
+            if (window[i] != needle[i]) {
                 // Sunday's trick: if we're going to jump, we might
                 // as well jump to line up the character *after* the
                 // current window.
@@ -376,6 +376,7 @@ STRINGLIB(_two_way)(const STRINGLIB_CHAR *haystack, Py_ssize_t len_haystack,
                 continue;
             }
 
+            i++;
             while (i < len_needle && needle[i] == window[i]) {
                 i++;
             }
@@ -681,3 +682,4 @@ FASTSEARCH(const STRINGLIB_CHAR* s, Py_ssize_t n,
         return -1;
     return count;
 }
+
Original file line number	Diff line number	Diff line change
`@@ -357,7 +357,7 @@ STRINGLIB(_two_way)(const STRINGLIB_CHAR *haystack, Py_ssize_t len_haystack,`
`357`	`357`	`LOG("\n> "); LOG("%*s", window - haystack + i, "");`
`358`	`358`	`LOG(" ^ <-- cut\n");`
`359`	`359`
`360`		`- if (window[i] != needle[i++]) {`
	`360`	`+ if (window[i] != needle[i]) {`
`361`	`361`	`// Sunday's trick: if we're going to jump, we might`
`362`	`362`	`// as well jump to line up the character after the`
`363`	`363`	`// current window.`
`@@ -376,6 +376,7 @@ STRINGLIB(_two_way)(const STRINGLIB_CHAR *haystack, Py_ssize_t len_haystack,`
`376`	`376`	`continue;`
`377`	`377`	`}`
`378`	`378`
	`379`	`+ i++;`
`379`	`380`	`while (i < len_needle && needle[i] == window[i]) {`
`380`	`381`	`i++;`
`381`	`382`	`}`
`@@ -681,3 +682,4 @@ FASTSEARCH(const STRINGLIB_CHAR* s, Py_ssize_t n,`
`681`	`682`	`return -1;`
`682`	`683`	`return count;`
`683`	`684`	`}`
	`685`	`+`