Add an unpatched version of xz, XZ Utils, to /trunk/deps/third_party

xz/src/liblzma/lzma/lzma_encoder_optimum_fast.c

+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file       lzma_encoder_optimum_fast.c
+//
+//  Author:     Igor Pavlov
+//
+//  This file has been put into the public domain.
+//  You can do whatever you want with this file.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#include "lzma_encoder_private.h"
+
+
+#define change_pair(small_dist, big_dist) \
+        (((big_dist) >> 7) > (small_dist))
+
+
+extern void
+lzma_lzma_optimum_fast(lzma_coder *restrict coder, lzma_mf *restrict mf,
+                uint32_t *restrict back_res, uint32_t *restrict len_res)
+{
+        const uint32_t nice_len = mf->nice_len;
+
+        uint32_t len_main;
+        uint32_t matches_count;
+        if (mf->read_ahead == 0) {
+                len_main = mf_find(mf, &matches_count, coder->matches);
+        } else {
+                assert(mf->read_ahead == 1);
+                len_main = coder->longest_match_length;
+                matches_count = coder->matches_count;
+        }
+
+        const uint8_t *buf = mf_ptr(mf) - 1;
+        const uint32_t buf_avail = my_min(mf_avail(mf) + 1, MATCH_LEN_MAX);
+
+        if (buf_avail < 2) {
+                // There's not enough input left to encode a match.
+                *back_res = UINT32_MAX;
+                *len_res = 1;
+                return;
+        }
+
+        // Look for repeated matches; scan the previous four match distances
+        uint32_t rep_len = 0;
+        uint32_t rep_index = 0;
+
+        for (uint32_t i = 0; i < REP_DISTANCES; ++i) {
+                // Pointer to the beginning of the match candidate
+                const uint8_t *const buf_back = buf - coder->reps[i] - 1;
+
+                // If the first two bytes (2 == MATCH_LEN_MIN) do not match,
+                // this rep is not useful.
+                if (not_equal_16(buf, buf_back))
+                        continue;
+
+                // The first two bytes matched.
+                // Calculate the length of the match.
+                uint32_t len;
+                for (len = 2; len < buf_avail
+                                && buf[len] == buf_back[len]; ++len) ;
+
+                // If we have found a repeated match that is at least
+                // nice_len long, return it immediately.
+                if (len >= nice_len) {
+                        *back_res = i;
+                        *len_res = len;
+                        mf_skip(mf, len - 1);
+                        return;
+                }
+
+                if (len > rep_len) {
+                        rep_index = i;
+                        rep_len = len;
+                }
+        }
+
+        // We didn't find a long enough repeated match. Encode it as a normal
+        // match if the match length is at least nice_len.
+        if (len_main >= nice_len) {
+                *back_res = coder->matches[matches_count - 1].dist
+                                + REP_DISTANCES;
+                *len_res = len_main;
+                mf_skip(mf, len_main - 1);
+                return;
+        }
+
+        uint32_t back_main = 0;
+        if (len_main >= 2) {
+                back_main = coder->matches[matches_count - 1].dist;
+
+                while (matches_count > 1 && len_main ==
+                                coder->matches[matches_count - 2].len + 1) {
+                        if (!change_pair(coder->matches[
+                                                matches_count - 2].dist,
+                                        back_main))
+                                break;
+
+                        --matches_count;
+                        len_main = coder->matches[matches_count - 1].len;
+                        back_main = coder->matches[matches_count - 1].dist;
+                }
+
+                if (len_main == 2 && back_main >= 0x80)
+                        len_main = 1;
+        }
+
+        if (rep_len >= 2) {
+                if (rep_len + 1 >= len_main
+                                || (rep_len + 2 >= len_main
+                                        && back_main > (UINT32_C(1) << 9))
+                                || (rep_len + 3 >= len_main
+                                        && back_main > (UINT32_C(1) << 15))) {
+                        *back_res = rep_index;
+                        *len_res = rep_len;
+                        mf_skip(mf, rep_len - 1);
+                        return;
+                }
+        }
+
+        if (len_main < 2 || buf_avail <= 2) {
+                *back_res = UINT32_MAX;
+                *len_res = 1;
+                return;
+        }
+
+        // Get the matches for the next byte. If we find a better match,
+        // the current byte is encoded as a literal.
+        coder->longest_match_length = mf_find(mf,
+                        &coder->matches_count, coder->matches);
+
+        if (coder->longest_match_length >= 2) {
+                const uint32_t new_dist = coder->matches[
+                                coder->matches_count - 1].dist;
+
+                if ((coder->longest_match_length >= len_main
+                                        && new_dist < back_main)
+                                || (coder->longest_match_length == len_main + 1
+                                        && !change_pair(back_main, new_dist))
+                                || (coder->longest_match_length > len_main + 1)
+                                || (coder->longest_match_length + 1 >= len_main
+                                        && len_main >= 3
+                                        && change_pair(new_dist, back_main))) {
+                        *back_res = UINT32_MAX;
+                        *len_res = 1;
+                        return;
+                }
+        }
+
+        // In contrast to LZMA SDK, dictionary could not have been moved
+        // between mf_find() calls, thus it is safe to just increment
+        // the old buf pointer instead of recalculating it with mf_ptr().
+        ++buf;
+
+        const uint32_t limit = len_main - 1;
+
+        for (uint32_t i = 0; i < REP_DISTANCES; ++i) {
+                const uint8_t *const buf_back = buf - coder->reps[i] - 1;
+
+                if (not_equal_16(buf, buf_back))
+                        continue;
+
+                uint32_t len;
+                for (len = 2; len < limit
+                                && buf[len] == buf_back[len]; ++len) ;
+
+                if (len >= limit) {
+                        *back_res = UINT32_MAX;
+                        *len_res = 1;
+                        return;
+                }
+        }
+
+        *back_res = back_main + REP_DISTANCES;
+        *len_res = len_main;
+        mf_skip(mf, len_main - 2);
+        return;
+}