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/*
* Copyright (c) 2015, Intel Corporation
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of Intel Corporation nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef ROSE_MIRACLE_H
#define ROSE_MIRACLE_H
#include "ue2common.h"
#include "runtime.h"
#include "rose_internal.h"
/** \brief Maximum number of bytes to scan when looking for a "miracle" stop
* character. */
#define MIRACLE_LEN_MAX 32
static really_inline
u64a roseMiracleScan(const u8 *stop, const u8 *d, const u8 *d_start) {
assert(d >= d_start);
// Note: unrolling this loop manually does appear to reduce its
// performance. I'm sick of tilting at this particular windmill.
u32 mshift = 0;
do {
u64a s = (u64a)stop[*d];
if (s) {
s <<= mshift;
return s;
}
mshift++;
} while (--d >= d_start);
return 0;
}
/**
* \brief "Miracle" scan: uses stop table to check if we can skip forward to a
* location where we know that the given rose engine will be in a known state.
*
* Scans the buffer/history between relative locations \a begin_loc and \a
* end_loc, and returns a miracle location (if any) that appears in the stream
* after \a begin_loc.
*
* Returns 1 if some bytes can be skipped and sets \a miracle_loc
* appropriately, 0 otherwise.
*/
static rose_inline
char roseMiracleOccurs(const struct RoseEngine *t,
const struct LeftNfaInfo *left,
const struct core_info *ci, const s64a begin_loc,
const s64a end_loc, s64a *miracle_loc) {
assert(!left->transient);
assert(left->stopTable);
DEBUG_PRINTF("looking for miracle over [%lld,%lld], maxLag=%u\n",
begin_loc, end_loc, left->maxLag);
DEBUG_PRINTF("ci->len=%zu, ci->hlen=%zu\n", ci->len, ci->hlen);
assert(begin_loc <= end_loc);
assert(begin_loc >= -(s64a)ci->hlen);
assert(end_loc <= (s64a)ci->len);
const u8 *stop = getByOffset(t, left->stopTable);
const s64a scan_end_loc = end_loc - left->maxLag;
if (scan_end_loc <= begin_loc) {
DEBUG_PRINTF("nothing to scan\n");
return 0;
}
const s64a start = MAX(begin_loc, scan_end_loc - MIRACLE_LEN_MAX);
DEBUG_PRINTF("scan [%lld..%lld]\n", start, scan_end_loc);
u64a s = 0; // state, on bits are miracle locations
// Scan buffer.
const s64a buf_scan_start = MAX(0, start);
if (scan_end_loc > buf_scan_start) {
const u8 *buf = ci->buf;
const u8 *d = buf + scan_end_loc - 1;
const u8 *d_start = buf + buf_scan_start;
s = roseMiracleScan(stop, d, d_start);
if (s) {
goto miracle_found;
}
}
// Scan history.
if (start < 0) {
const u8 *hbuf_end = ci->hbuf + ci->hlen;
const u8 *d = hbuf_end + MIN(0, scan_end_loc) - 1;
const u8 *d_start = hbuf_end + start;
s = roseMiracleScan(stop, d, d_start);
if (scan_end_loc > 0) {
// Shift s over to account for the buffer scan above.
s <<= scan_end_loc;
}
}
if (s) {
miracle_found:
DEBUG_PRINTF("s=0x%llx, ctz=%u\n", s, ctz64(s));
s64a loc = end_loc - left->maxLag - ctz64(s) - 1;
if (loc > begin_loc) {
DEBUG_PRINTF("miracle at %lld\n", loc);
*miracle_loc = loc;
return 1;
}
}
DEBUG_PRINTF("no viable miraculous stop characters found\n");
return 0;
}
#endif // ROSE_MIRACLE_H
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