rewrite strstr to do c-style comparisons, to avoid js regexp search artifacts

src/library.js

@@ -4286,10 +4286,20 @@ LibraryManager.library = {
   },
 
   strstr: function(ptr1, ptr2) {
-    var str1 = Pointer_stringify(ptr1);
-    var str2 = Pointer_stringify(ptr2);
-    var ret = str1.search(str2);
-    return ret >= 0 ? ptr1 + ret : 0;
+    var check = 0, start;
+    do {
+      var curr1 = {{{ makeGetValue('ptr1++', 0, 'i8') }}};
+      if (!check) check = start = ptr2;
+      var curr2 = {{{ makeGetValue('check++', 0, 'i8') }}};
+      if (curr2 == 0) return start;
+      if (curr2 != curr1) {
+        // rewind to one character after start, to find ez in eeez
+        var diff = check - start - 1;
+        ptr1 -= diff;
+        check = 0;
+      }
+    } while (curr1);
+    return 0;
   },
 
   strchr: function(ptr, chr) {

tests/runner.py

@@ -3979,6 +3979,64 @@ at function.:blag
         '''
       self.do_run(src, '0*0*0*0*6*5*4*3*3*9*8')
 
+    def test_strstr(self):
+      src = r'''
+        #include <stdio.h>
+        #include <string.h>
+
+        int main()
+        {
+          printf("%d\n", !!strstr("\\n", "\\n"));
+          printf("%d\n", !!strstr("cheezy", "ez"));
+          printf("%d\n", !!strstr("cheeezy", "ez"));
+          printf("%d\n", !!strstr("cheeeeeeeeeezy", "ez"));
+          printf("%d\n", !!strstr("cheeeeeeeeee1zy", "ez"));
+          printf("%d\n", !!strstr("che1ezy", "ez"));
+          printf("%d\n", !!strstr("che1ezy", "che"));
+          printf("%d\n", !!strstr("ce1ezy", "che"));
+          printf("%d\n", !!strstr("ce1ezy", "ezy"));
+          printf("%d\n", !!strstr("ce1ezyt", "ezy"));
+          printf("%d\n", !!strstr("ce1ez1y", "ezy"));
+          printf("%d\n", !!strstr("cheezy", "a"));
+          printf("%d\n", !!strstr("cheezy", "b"));
+          printf("%d\n", !!strstr("cheezy", "c"));
+          printf("%d\n", !!strstr("cheezy", "d"));
+          printf("%d\n", !!strstr("cheezy", "g"));
+          printf("%d\n", !!strstr("cheezy", "h"));
+          printf("%d\n", !!strstr("cheezy", "i"));
+          printf("%d\n", !!strstr("cheezy", "e"));
+          printf("%d\n", !!strstr("cheezy", "x"));
+          printf("%d\n", !!strstr("cheezy", "y"));
+          printf("%d\n", !!strstr("cheezy", "z"));
+          printf("%d\n", !!strstr("cheezy", "_"));
+          return 0;
+        }
+      '''
+      self.do_run(src, '''1
+1
+1
+1
+0
+1
+1
+0
+1
+1
+0
+0
+0
+1
+0
+0
+1
+0
+1
+0
+1
+1
+0
+''')
+
     def test_sscanf(self):
       src = r'''
         #include <stdio.h>