Allow disabling Castagnoli compression optimization

Faster symbol hashing has a positive impact on data compression speed
(around 20% on Intel and 36% on Arm Cortex big cores).

A misfeature is that the generated compressed output will differ from
vanilla zlib (even though it is still valid 'DEFLATE-d' content) and in
some cases has slightly better compression ratio.

We offer here a way to disable the optimization if there is the expectation
that compressed content should match when compared to vanilla zlib.

Bug: 990489
Change-Id: I910e140eb15dd334eb869b078f940581249a7e6d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1742297
Reviewed-by: Adenilson Cavalcanti <cavalcantii@chromium.org>
Reviewed-by: Chris Blume <cblume@chromium.org>
Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#685041}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 5b8477c39bb70cb1cbb8bbbc8149674fa65f1c91

1 files changed, 11 insertions, 1 deletions

diff --git a/deflate.c b/deflate.c
index 98da939..c950d6f 100644
--- a/deflate.c
+++ b/deflate.c
@@ -215,13 +215,23 @@ local INLINE Pos insert_string_c(deflate_state *const s, const Pos str)
 
 local INLINE Pos insert_string(deflate_state *const s, const Pos str)
 {
+/* String dictionary insertion: faster symbol hashing has a positive impact
+ * on data compression speeds (around 20% on Intel and 36% on ARM Cortex big
+ * cores).
+ * A misfeature is that the generated compressed output will differ from
+ * vanilla zlib (even though it is still valid 'DEFLATE-d' content).
+ *
+ * We offer here a way to disable the optimization if there is the expectation
+ * that compressed content should match when compared to vanilla zlib.
+ */
+#if !defined(CHROMIUM_ZLIB_NO_CASTAGNOLI)
 #if defined(CRC32_ARMV8_CRC32)
     if (arm_cpu_enable_crc32)
         return insert_string_arm(s, str);
 #endif
     if (x86_cpu_enable_simd)
         return insert_string_sse(s, str);
-
+#endif
     return insert_string_c(s, str);
 }