Document the optional zlib library in MS-Windows builds

* nt/README.W32:
* nt/INSTALL.W64:
* nt/INSTALL: Mention the optional text decompression support and
the zlib library.

3 files changed, 29 insertions, 4 deletions

diff --git a/nt/INSTALL b/nt/INSTALL
index 99a2f3988f9..fff0eb6f8d9 100644
--- a/nt/INSTALL
+++ b/nt/INSTALL
@@ -784,6 +784,15 @@ build will run on Windows 9X and newer systems).
   You need the libiconv-X.Y.Z-N-mingw32-dev.tar.lzma tarball from that
   site.
 
+* Optional support for decompressing text
+
+  Emacs can decompress text if compiled with the zlib library.
+  Prebuilt binaries of zlib DLL (for 32-bit builds of Emacs) are
+  available from the ezwinports site; see above for the URL.
+
+  (This library is also a prerequisite for several image libraries, so
+  you may already have it; look for zlib1.dll or libz-1.dll.)
+
 
 This file is part of GNU Emacs.
 
diff --git a/nt/INSTALL.W64 b/nt/INSTALL.W64
index e109c6f0f23..40670a6a878 100644
--- a/nt/INSTALL.W64
+++ b/nt/INSTALL.W64
@@ -64,13 +64,15 @@ packages (you can copy and paste it into the shell with Shift + Insert):
   mingw-w64-x86_64-libjpeg-turbo \
   mingw-w64-x86_64-librsvg \
   mingw-w64-x86_64-libxml2 \
-  mingw-w64-x86_64-gnutls
+  mingw-w64-x86_64-gnutls \
+  mingw-w64-x86_64-zlib
 
 The packages include the base developer tools (autoconf, automake, grep, make,
 etc.), the compiler toolchain (gcc, gdb, etc.), several image libraries, an
-XML library, and the GnuTLS (transport layer security) library.  Only the
-first three packages are required (base-devel, toolchain, xpm-nox); the rest
-are optional.
+XML library, the GnuTLS (transport layer security) library, and zlib for
+decompressing text.  Only the first three packages are required (base-devel,
+toolchain, xpm-nox); the rest are optional.  You can select only part of the
+libraries if you don't need them all.
 
 You now have a complete build environment for Emacs.
 
diff --git a/nt/README.W32 b/nt/README.W32
index d16ec8e319f..a061596da55 100644
--- a/nt/README.W32
+++ b/nt/README.W32
@@ -212,6 +212,20 @@ See the end of the file for license conditions.
   You can get pre-built binaries (including any required DLL and the
   header files) at http://sourceforge.net/projects/ezwinports/files/.
 
+
+* zlib support
+
+  zlib provides support for decompressing text, which is necessary for
+  the zlib-decompress-region primitive.
+
+  Prebuilt binaries of zlib DLL (for 32-bit builds of Emacs) are
+  available from the ezwinports site; see above for the URL.  For the
+  64-bit DLL, see the instructions below for installing from MSYS2
+  site.
+
+  (This library is also a prerequisite for several image libraries, so
+  you may already have it; look for zlib1.dll or libz-1.dll.)
+
 * Installing 64-bit optional libraries from the MSYS2 site
 
   We recommend that you use the 'pacman' utility to download the