unconditionally use 'deflateBound' when zlib is enabled

When Graphviz was built with support for zlib-based compression, it would only
use `deflateBound` if it was discovered at build time. The `deflateBound` code
path provides a tighter estimate of final compressed size, allowing compression
to minimize its intermediate heap allocations.

The CMake build system did not attempt to discover the presence of
`deflateBound` (config-cmake.in). The Windows build hard coded `deflateBound` as
unavailable (windows/include/config.h). So both these builds would result in a
Graphviz that would use more memory than necessary when writing compressed
output formats.

`deflateBound` arrived in zlib 1.2.0, released on 2003-03-09. It seems safe to
unconditionally assume its existence in 2022. The estimate `deflateBound`
provides has improved in successive releases, with even the latest zlib 1.2.13
released on 2022-10-13 further tightening its estimate. So it is expected that
Graphviz users, with this change, will get lower memory usage during writing
compressed formats, and then lower still as newer zlib releases propagate
through the ecosystem.

diff --git a/CHANGELOG.md b/CHANGELOG.md
index aa436bbe3951f3253c86647e53c304e240e86fc6..2ab04f141a2a542cf88bab97e8d24f11e86f400c 100644 (file)
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased (7.0.1)]
 
+### Changed
+
+- When built with zlib support, Graphviz will unconditionally use
+  `deflateBound`. The only user-visible effect should be slightly decreased
+  memory usage when using a zlib-compressed output format.
+
 ### Fixed
 
 - Failure of arrowhead and arrowtail to respect penwidth #372 \

diff --git a/configure.ac b/configure.ac
index 381febd57a9ea15ef64d5b1e227a39e48c5669eb..75410b07efd38e564c82a19bdcfd22c2cfde6398 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -1620,7 +1620,6 @@ AC_CHECK_HEADER(zlib.h,
                        AC_MSG_WARN(Optional z library not available))],
        AC_MSG_WARN(Optional z library not available - no zlib.h))
        LDFLAGS="$LDFLAGS $Z_LIBS"
-        AC_CHECK_FUNCS(deflateBound)
 LDFLAGS=$save_LDFLAGS
 CPPFLAGS=$save_CPPFLAGS
 AC_SUBST([Z_INCLUDES])

diff --git a/lib/gvc/gvdevice.c b/lib/gvc/gvdevice.c
index 0ab0e45b069acf079b3815b2fc616b89725317f5..32120da0728529d01f2f4a798f6d69b5e8d49197 100644 (file)
--- a/lib/gvc/gvdevice.c
+++ b/lib/gvc/gvdevice.c
@@ -205,14 +205,8 @@ size_t gvwrite (GVJ_t * job, const char *s, size_t len)
     if (job->flags & GVDEVICE_COMPRESSED_FORMAT) {
 #ifdef HAVE_LIBZ
        z_streamp z = &z_strm;
-       size_t dflen;
 
-#ifdef HAVE_DEFLATEBOUND
-       dflen = deflateBound(z, len);
-#else
-       /* deflateBound() is not available in older libz, e.g. from centos3 */
-       dflen = 2 * len  + dfallocated - z->avail_out;
-#endif
+       size_t dflen = deflateBound(z, len);
        if (dfallocated < dflen) {
            dfallocated = (dflen + 1 + PAGE_ALIGN) & ~PAGE_ALIGN;
            df = realloc(df, dfallocated);

diff --git a/windows/include/config.h b/windows/include/config.h
index c2152ac33056d44ad250d2401aebaa07b870229c..d67a9a25bde0fd8f95e6b977299ee41ab571fb74 100644 (file)
--- a/windows/include/config.h
+++ b/windows/include/config.h
@@ -33,9 +33,6 @@
 /* Define if you have the ann library */
 #define HAVE_ANN 1
 
-/* Define to 1 if you have the `deflateBound' function. */
-/* #undef HAVE_DEFLATEBOUND */
-
 /* Define if you have the DevIL library */
 /* #undef HAVE_DEVIL */