mlibc: Implement strstr.

* lib/libc+tcc.c (_memmem, memmem): New function.  Import from GNU
  LilyPond.
  (strstr): Implement using memmem.
* include/string.h (_memmem, memmem): Declare.
* AUTHORS: Add Han-Wen Nienhuys.

AUTHORS

@@ -5,7 +5,8 @@ All files except the imported files listed below
 Jeremiah Orians <jeremiah@pdp10.guru>
 lib/libc.c (fopen)
 
-
+Han-Wen Nienhuys <hanwen@xs4all.nl>
+lib/libc+tcc.c (_memmem, memmem)
 
 List of imported files
 

lib/libc+tcc.c

@@ -1,6 +1,7 @@
 /* -*-comment-start: "//";comment-end:""-*-
  * Mes --- Maxwell Equations of Software
  * Copyright © 2017,2018 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+ * Copyright (C) 2018 Han-Wen Nienhuys <hanwen@xs4all.nl>
  *
  * This file is part of Mes.
  *
@@ -287,11 +288,50 @@ strrchr (char const *s, int c)
   return 0;
 }
 
+/** locate a substring. #memmem# finds the first occurrence of
+    #needle# in #haystack#.  This is not ANSI-C.
+
+    The prototype is not in accordance with the Linux Programmer's
+    Manual v1.15, but it is with /usr/include/string.h   */
+
+unsigned char *
+_memmem (unsigned char const *haystack, int haystack_len,
+         unsigned char const *needle, int needle_len)
+{
+  unsigned char const *end_haystack = haystack + haystack_len - needle_len + 1;
+  unsigned char const *end_needle = needle + needle_len;
+
+  /* Ahhh ... Some minimal lowlevel stuff. This *is* nice; Varation
+     is the spice of life */
+  while (haystack < end_haystack)
+    {
+      unsigned char const *subneedle = needle;
+      unsigned char const *subhaystack = haystack;
+      while (subneedle < end_needle)
+        if (*subneedle++ != *subhaystack++)
+          goto next;
+
+      /* Completed the needle.  Gotcha.  */
+      return (unsigned char *) haystack;
+    next:
+      haystack++;
+    }
+  return 0;
+}
+
+void *
+memmem (void const *haystack, int haystack_len,
+        void const *needle, int needle_len)
+{
+  unsigned char const *haystack_byte_c = (unsigned char const *)haystack;
+  unsigned char const *needle_byte_c = (unsigned char const *)needle;
+  return _memmem (haystack_byte_c, haystack_len, needle_byte_c, needle_len);
+}
+
 char *
 strstr (char const *haystack, char const *needle)
 {
-  eputs ("strstr stub\n");
+  return memmem (haystack, strlen (haystack), needle, strlen (needle));
-  return 0;
 }
 
 double