Remove x86_check_features() from inflate

adler32 can be freely called like crc32, per the "zlib.h" docs
so move the x86 feature check there, which allows us to remove
x86_check_features() from zlib inflate. Note inflate() calls

  adler32(0, Z_NULL, 0);

(once only) before using the zlib adler32() routine. A reading
from third_party/libpng png.c

  2324:  /* Now calculate the adler32 if not done already. */
  2327:     adler = adler32(0, NULL, 0);
  2328:     adler = adler32(adler, profile, length);

suggests they also conform to the "zlib.h" doc rules about use
of the adler32 routine.

Bug: 762564
Change-Id: Id84da0eb52bc10edb541a284eab9aef652ba2c72
Reviewed-on: https://chromium-review.googlesource.com/901043
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#534964}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: c376937e3709ddef4b97621a58039a21b67faa6e

1 files changed, 15 insertions, 0 deletions

diff --git a/adler32.c b/adler32.c
index 03491b9..a42f35f 100644
--- a/adler32.c
+++ b/adler32.c
@@ -98,9 +98,24 @@ uLong ZEXPORT adler32_z(adler, buf, len)
         return adler | (sum2 << 16);
     }
 
+#if defined(ADLER32_SIMD_SSSE3)
+    /*
+     * Use SSSE3 to compute the adler32. Since this routine can be
+     * freely used, check CPU features here. zlib convention is to
+     * call adler32(0, NULL, 0), before making calls to adler32().
+     * So this is a good early (and infrequent) place to cache CPU
+     * features for those later, more interesting adler32() calls.
+     */
+    if (buf == Z_NULL) {
+        if (!len) /* Assume user is calling adler32(0, NULL, 0); */
+            x86_check_features();
+        return 1L;
+    }
+#else
     /* initial Adler-32 value (deferred check for len == 1 speed) */
     if (buf == Z_NULL)
         return 1L;
+#endif
 
     /* in case short lengths are provided, keep it somewhat fast */
     if (len < 16) {