Make strstr and strcasestr O(n), not O(n^2); add memmem.

* libc/string/str-two-way.h: New file.
* libc/string/memmem.c (memmem): New file.
* libc/include/string.h (memmem): Declare for all platforms.
* libc/string/strstr.c (strstr): Provide O(n) implementation when
not optimizing for space.
* libc/string/strcasestr.c (strcasestr): Likewise.
* libc/string/Makefile.am (ELIX_SOURCES): Rename to...
(ELIX_2_SOURCES): ...this.
(ELIX_4_SOURCES): New category, for memmem.
(lib_a_SOURCES, libstring_la_SOURCES): Build new file.
(CHEWOUT_FILES): Build documentation for memmem.
* libc/string/strings.tex: Include new docs.

1 files changed, 4 insertions, 0 deletions

diff --git a/newlib/libc/string/strings.tex b/newlib/libc/string/strings.tex
index 5ba6e0fe5..6750f3eb0 100644
--- a/newlib/libc/string/strings.tex
+++ b/newlib/libc/string/strings.tex
@@ -14,6 +14,7 @@ managing areas of memory.  The corresponding declarations are in
 * memchr::      Find character in memory
 * memcmp::      Compare two memory areas
 * memcpy::      Copy memory regions
+* memmem::      Find memory segment
 * memmove::     Move possibly overlapping memory
 * mempcpy::	Copy memory regions and locate end
 * memset::      Set an area of memory
@@ -72,6 +73,9 @@ managing areas of memory.  The corresponding declarations are in
 @include string/memcpy.def
 
 @page
+@include string/memmem.def
+
+@page
 @include string/memmove.def
 
 @page