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121 lines
4.6 KiB
Diff
121 lines
4.6 KiB
Diff
From 8626f3ea324e1e6f15229722761617063a70b96b Mon Sep 17 00:00:00 2001
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From: Chris Blume <cblume@google.com>
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Date: Tue, 12 Sep 2017 11:17:55 -0700
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Subject: [PATCH 1/1] Zlib: Use defines for inffast
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Zlib's inffast uses a handful of magic numbers. It would be easier to
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read and maintain if these magic numbers were instead #defines.
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NigelTao@ wrote this code to clean up the magic numbers in
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https://chromium-review.googlesource.com/c/chromium/src/+/601694
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Nigel gave me permission to make a separate pull request to separate out
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just the magic number cleaning.
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BUG=764431
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---
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third_party/zlib/infback.c | 3 ++-
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third_party/zlib/inffast.c | 15 +++++++++------
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third_party/zlib/inffast.h | 15 +++++++++++++++
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third_party/zlib/inflate.c | 3 ++-
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4 files changed, 28 insertions(+), 8 deletions(-)
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diff --git a/third_party/zlib/infback.c b/third_party/zlib/infback.c
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index 59679ecbfc5d..b93ef478e957 100644
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--- a/third_party/zlib/infback.c
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+++ b/third_party/zlib/infback.c
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@@ -480,7 +480,8 @@ void FAR *out_desc;
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case LEN:
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/* use inflate_fast() if we have enough input and output */
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- if (have >= 6 && left >= 258) {
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+ if (have >= INFLATE_FAST_MIN_HAVE &&
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+ left >= INFLATE_FAST_MIN_LEFT) {
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RESTORE();
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if (state->whave < state->wsize)
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state->whave = state->wsize - left;
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diff --git a/third_party/zlib/inffast.c b/third_party/zlib/inffast.c
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index 0dbd1dbc09f2..66c0d02494a9 100644
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--- a/third_party/zlib/inffast.c
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+++ b/third_party/zlib/inffast.c
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@@ -23,8 +23,8 @@
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Entry assumptions:
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state->mode == LEN
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- strm->avail_in >= 6
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- strm->avail_out >= 258
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+ strm->avail_in >= INFLATE_FAST_MIN_HAVE
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+ strm->avail_out >= INFLATE_FAST_MIN_LEFT
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start >= strm->avail_out
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state->bits < 8
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@@ -80,10 +80,10 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
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/* copy state to local variables */
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state = (struct inflate_state FAR *)strm->state;
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in = strm->next_in;
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- last = in + (strm->avail_in - 5);
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+ last = in + (strm->avail_in - (INFLATE_FAST_MIN_HAVE - 1));
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out = strm->next_out;
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beg = out - (start - strm->avail_out);
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- end = out + (strm->avail_out - 257);
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+ end = out + (strm->avail_out - (INFLATE_FAST_MIN_LEFT - 1));
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#ifdef INFLATE_STRICT
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dmax = state->dmax;
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#endif
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@@ -298,9 +298,12 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
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/* update state and return */
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strm->next_in = in;
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strm->next_out = out;
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- strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
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+ strm->avail_in = (unsigned)(in < last ?
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+ (INFLATE_FAST_MIN_HAVE - 1) + (last - in) :
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+ (INFLATE_FAST_MIN_HAVE - 1) - (in - last));
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strm->avail_out = (unsigned)(out < end ?
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- 257 + (end - out) : 257 - (out - end));
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+ (INFLATE_FAST_MIN_LEFT - 1) + (end - out) :
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+ (INFLATE_FAST_MIN_LEFT - 1) - (out - end));
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state->hold = hold;
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state->bits = bits;
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return;
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diff --git a/third_party/zlib/inffast.h b/third_party/zlib/inffast.h
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index e5c1aa4ca8cd..dda6bc82cc3b 100644
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--- a/third_party/zlib/inffast.h
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+++ b/third_party/zlib/inffast.h
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@@ -8,4 +8,19 @@
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subject to change. Applications should only use zlib.h.
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*/
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+
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+/* INFLATE_FAST_MIN_LEFT is the minimum number of output bytes that are left,
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+ so that we can call inflate_fast safely with only one up front bounds check.
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+ One length-distance code pair can copy up to 258 bytes.
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+ */
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+#define INFLATE_FAST_MIN_LEFT 258
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+
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+/* INFLATE_FAST_MIN_HAVE is the minimum number of input bytes that we have, so
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+ that we can call inflate_fast safely with only one up front bounds check.
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+ One length-distance code pair (as two Huffman encoded values of up to 15
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+ bits each) plus any additional bits (up to 5 for length and 13 for distance)
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+ can require reading up to 48 bits, or 6 bytes.
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+ */
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+#define INFLATE_FAST_MIN_HAVE 6
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+
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void ZLIB_INTERNAL inflate_fast OF((z_streamp strm, unsigned start));
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diff --git a/third_party/zlib/inflate.c b/third_party/zlib/inflate.c
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index cc38b983485b..257b9a982668 100644
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--- a/third_party/zlib/inflate.c
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+++ b/third_party/zlib/inflate.c
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@@ -1044,7 +1044,8 @@ int flush;
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case LEN_:
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state->mode = LEN;
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case LEN:
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- if (have >= 6 && left >= 258) {
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+ if (have >= INFLATE_FAST_MIN_HAVE &&
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+ left >= INFLATE_FAST_MIN_LEFT) {
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RESTORE();
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inflate_fast(strm, out);
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LOAD();
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--
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2.14.1.581.gf28d330327-goog
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