From 8626f3ea324e1e6f15229722761617063a70b96b Mon Sep 17 00:00:00 2001
From: Chris Blume <cblume@google.com>
Date: Tue, 12 Sep 2017 11:17:55 -0700
Subject: [PATCH 1/1] Zlib: Use defines for inffast

Zlib's inffast uses a handful of magic numbers. It would be easier to
read and maintain if these magic numbers were instead #defines.

NigelTao@ wrote this code to clean up the magic numbers in
https://chromium-review.googlesource.com/c/chromium/src/+/601694

Nigel gave me permission to make a separate pull request to separate out
just the magic number cleaning.

BUG=764431
---
 third_party/zlib/infback.c |  3 ++-
 third_party/zlib/inffast.c | 15 +++++++++------
 third_party/zlib/inffast.h | 15 +++++++++++++++
 third_party/zlib/inflate.c |  3 ++-
 4 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/third_party/zlib/infback.c b/third_party/zlib/infback.c
index 59679ecbfc5d..b93ef478e957 100644
--- a/third_party/zlib/infback.c
+++ b/third_party/zlib/infback.c
@@ -480,7 +480,8 @@ void FAR *out_desc;
 
         case LEN:
             /* use inflate_fast() if we have enough input and output */
-            if (have >= 6 && left >= 258) {
+            if (have >= INFLATE_FAST_MIN_HAVE &&
+                left >= INFLATE_FAST_MIN_LEFT) {
                 RESTORE();
                 if (state->whave < state->wsize)
                     state->whave = state->wsize - left;
diff --git a/third_party/zlib/inffast.c b/third_party/zlib/inffast.c
index 0dbd1dbc09f2..66c0d02494a9 100644
--- a/third_party/zlib/inffast.c
+++ b/third_party/zlib/inffast.c
@@ -23,8 +23,8 @@
    Entry assumptions:
 
         state->mode == LEN
-        strm->avail_in >= 6
-        strm->avail_out >= 258
+        strm->avail_in >= INFLATE_FAST_MIN_HAVE
+        strm->avail_out >= INFLATE_FAST_MIN_LEFT
         start >= strm->avail_out
         state->bits < 8
 
@@ -80,10 +80,10 @@ unsigned start;         /* inflate()'s starting value for strm->avail_out */
     /* copy state to local variables */
     state = (struct inflate_state FAR *)strm->state;
     in = strm->next_in;
-    last = in + (strm->avail_in - 5);
+    last = in + (strm->avail_in - (INFLATE_FAST_MIN_HAVE - 1));
     out = strm->next_out;
     beg = out - (start - strm->avail_out);
-    end = out + (strm->avail_out - 257);
+    end = out + (strm->avail_out - (INFLATE_FAST_MIN_LEFT - 1));
 #ifdef INFLATE_STRICT
     dmax = state->dmax;
 #endif
@@ -298,9 +298,12 @@ unsigned start;         /* inflate()'s starting value for strm->avail_out */
     /* update state and return */
     strm->next_in = in;
     strm->next_out = out;
-    strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
+    strm->avail_in = (unsigned)(in < last ?
+        (INFLATE_FAST_MIN_HAVE - 1) + (last - in) :
+        (INFLATE_FAST_MIN_HAVE - 1) - (in - last));
     strm->avail_out = (unsigned)(out < end ?
-                                 257 + (end - out) : 257 - (out - end));
+        (INFLATE_FAST_MIN_LEFT - 1) + (end - out) :
+        (INFLATE_FAST_MIN_LEFT - 1) - (out - end));
     state->hold = hold;
     state->bits = bits;
     return;
diff --git a/third_party/zlib/inffast.h b/third_party/zlib/inffast.h
index e5c1aa4ca8cd..dda6bc82cc3b 100644
--- a/third_party/zlib/inffast.h
+++ b/third_party/zlib/inffast.h
@@ -8,4 +8,19 @@
    subject to change. Applications should only use zlib.h.
  */
 
+
+/* INFLATE_FAST_MIN_LEFT is the minimum number of output bytes that are left,
+   so that we can call inflate_fast safely with only one up front bounds check.
+   One length-distance code pair can copy up to 258 bytes.
+ */
+#define INFLATE_FAST_MIN_LEFT 258
+
+/* INFLATE_FAST_MIN_HAVE is the minimum number of input bytes that we have, so
+   that we can call inflate_fast safely with only one up front bounds check.
+   One length-distance code pair (as two Huffman encoded values of up to 15
+   bits each) plus any additional bits (up to 5 for length and 13 for distance)
+   can require reading up to 48 bits, or 6 bytes.
+ */
+#define INFLATE_FAST_MIN_HAVE 6
+
 void ZLIB_INTERNAL inflate_fast OF((z_streamp strm, unsigned start));
diff --git a/third_party/zlib/inflate.c b/third_party/zlib/inflate.c
index cc38b983485b..257b9a982668 100644
--- a/third_party/zlib/inflate.c
+++ b/third_party/zlib/inflate.c
@@ -1044,7 +1044,8 @@ int flush;
         case LEN_:
             state->mode = LEN;
         case LEN:
-            if (have >= 6 && left >= 258) {
+            if (have >= INFLATE_FAST_MIN_HAVE &&
+                left >= INFLATE_FAST_MIN_LEFT) {
                 RESTORE();
                 inflate_fast(strm, out);
                 LOAD();
-- 
2.14.1.581.gf28d330327-goog