Use atomics to build inflate fixed tables once.

This moves the once code from crc32.c to zutil.c, and uses it also
for building the inflate fixed tables when BUILDFIXED is defined.
The fixed tables are now housed in inftrees.c, shared by inflate.c
and infback.c. The once() function is now external, and so is
renamed to z_once() to avoid name collisions.

If either BUILDFIXED or DYNAMIC_CRC_TABLE is defined, and atomics
are not available, then a warning is issued noting that zlib is not
thread-safe.

1 files changed, 26 insertions, 0 deletions

diff --git a/zutil.h b/zutil.h
index 27ca693..94fa1af 100644
--- a/zutil.h
+++ b/zutil.h
@@ -254,4 +254,30 @@ extern z_const char * const z_errmsg[10]; /* indexed by 2-zlib_error */
 #define ZSWAP32(q) ((((q) >> 24) & 0xff) + (((q) >> 8) & 0xff00) + \
                     (((q) & 0xff00) << 8) + (((q) & 0xff) << 24))
 
+#ifdef MAKEFIXED
+#  ifndef BUILDFIXED
+#    define BUILDFIXED
+#  endif
+#endif
+#if defined(BUILDFIXED) || defined(DYNAMIC_CRC_TABLE)
+/* Structure for z_once(), which must be initialized with Z_ONCE_INIT. */
+typedef struct z_once_s z_once_t;
+void ZLIB_INTERNAL z_once(z_once_t *state, void (*init)(void));
+#if defined(__STDC__) && __STDC_VERSION__ >= 201112L && \
+    !defined(__STDC_NO_ATOMICS__)
+#include <stdatomic.h>
+struct z_once_s {
+    atomic_flag begun;
+    atomic_int done;
+};
+#define Z_ONCE_INIT {ATOMIC_FLAG_INIT, 0}
+#else   /* no atomics! */
+struct z_once_s {
+    volatile int begun;
+    volatile int done;
+};
+#define Z_ONCE_INIT {0, 0}
+#endif
+#endif
+
 #endif /* ZUTIL_H */