229 lines
7.0 KiB
JavaScript
229 lines
7.0 KiB
JavaScript
'use strict'
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/**
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* Copyright Brian White. All rights reserved.
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*
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* @see https://github.com/mscdex/streamsearch
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to
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* deal in the Software without restriction, including without limitation the
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* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
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* sell copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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* IN THE SOFTWARE.
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*
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* Based heavily on the Streaming Boyer-Moore-Horspool C++ implementation
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* by Hongli Lai at: https://github.com/FooBarWidget/boyer-moore-horspool
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*/
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const EventEmitter = require('node:events').EventEmitter
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const inherits = require('node:util').inherits
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function SBMH (needle) {
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if (typeof needle === 'string') {
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needle = Buffer.from(needle)
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}
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if (!Buffer.isBuffer(needle)) {
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throw new TypeError('The needle has to be a String or a Buffer.')
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}
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const needleLength = needle.length
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if (needleLength === 0) {
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throw new Error('The needle cannot be an empty String/Buffer.')
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}
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if (needleLength > 256) {
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throw new Error('The needle cannot have a length bigger than 256.')
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}
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this.maxMatches = Infinity
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this.matches = 0
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this._occ = new Array(256)
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.fill(needleLength) // Initialize occurrence table.
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this._lookbehind_size = 0
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this._needle = needle
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this._bufpos = 0
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this._lookbehind = Buffer.alloc(needleLength)
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// Populate occurrence table with analysis of the needle,
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// ignoring last letter.
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for (var i = 0; i < needleLength - 1; ++i) { // eslint-disable-line no-var
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this._occ[needle[i]] = needleLength - 1 - i
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}
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}
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inherits(SBMH, EventEmitter)
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SBMH.prototype.reset = function () {
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this._lookbehind_size = 0
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this.matches = 0
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this._bufpos = 0
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}
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SBMH.prototype.push = function (chunk, pos) {
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if (!Buffer.isBuffer(chunk)) {
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chunk = Buffer.from(chunk, 'binary')
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}
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const chlen = chunk.length
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this._bufpos = pos || 0
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let r
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while (r !== chlen && this.matches < this.maxMatches) { r = this._sbmh_feed(chunk) }
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return r
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}
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SBMH.prototype._sbmh_feed = function (data) {
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const len = data.length
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const needle = this._needle
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const needleLength = needle.length
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const lastNeedleChar = needle[needleLength - 1]
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// Positive: points to a position in `data`
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// pos == 3 points to data[3]
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// Negative: points to a position in the lookbehind buffer
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// pos == -2 points to lookbehind[lookbehind_size - 2]
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let pos = -this._lookbehind_size
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let ch
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if (pos < 0) {
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// Lookbehind buffer is not empty. Perform Boyer-Moore-Horspool
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// search with character lookup code that considers both the
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// lookbehind buffer and the current round's haystack data.
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//
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// Loop until
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// there is a match.
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// or until
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// we've moved past the position that requires the
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// lookbehind buffer. In this case we switch to the
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// optimized loop.
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// or until
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// the character to look at lies outside the haystack.
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while (pos < 0 && pos <= len - needleLength) {
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ch = this._sbmh_lookup_char(data, pos + needleLength - 1)
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if (
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ch === lastNeedleChar &&
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this._sbmh_memcmp(data, pos, needleLength - 1)
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) {
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this._lookbehind_size = 0
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++this.matches
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this.emit('info', true)
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return (this._bufpos = pos + needleLength)
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}
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pos += this._occ[ch]
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}
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// No match.
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if (pos < 0) {
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// There's too few data for Boyer-Moore-Horspool to run,
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// so let's use a different algorithm to skip as much as
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// we can.
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// Forward pos until
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// the trailing part of lookbehind + data
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// looks like the beginning of the needle
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// or until
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// pos == 0
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while (pos < 0 && !this._sbmh_memcmp(data, pos, len - pos)) { ++pos }
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}
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if (pos >= 0) {
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// Discard lookbehind buffer.
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this.emit('info', false, this._lookbehind, 0, this._lookbehind_size)
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this._lookbehind_size = 0
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} else {
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// Cut off part of the lookbehind buffer that has
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// been processed and append the entire haystack
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// into it.
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const bytesToCutOff = this._lookbehind_size + pos
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if (bytesToCutOff > 0) {
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// The cut off data is guaranteed not to contain the needle.
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this.emit('info', false, this._lookbehind, 0, bytesToCutOff)
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}
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this._lookbehind.copy(this._lookbehind, 0, bytesToCutOff,
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this._lookbehind_size - bytesToCutOff)
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this._lookbehind_size -= bytesToCutOff
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data.copy(this._lookbehind, this._lookbehind_size)
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this._lookbehind_size += len
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this._bufpos = len
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return len
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}
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}
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pos += (pos >= 0) * this._bufpos
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// Lookbehind buffer is now empty. We only need to check if the
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// needle is in the haystack.
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if (data.indexOf(needle, pos) !== -1) {
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pos = data.indexOf(needle, pos)
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++this.matches
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if (pos > 0) { this.emit('info', true, data, this._bufpos, pos) } else { this.emit('info', true) }
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return (this._bufpos = pos + needleLength)
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} else {
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pos = len - needleLength
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}
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// There was no match. If there's trailing haystack data that we cannot
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// match yet using the Boyer-Moore-Horspool algorithm (because the trailing
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// data is less than the needle size) then match using a modified
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// algorithm that starts matching from the beginning instead of the end.
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// Whatever trailing data is left after running this algorithm is added to
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// the lookbehind buffer.
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while (
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pos < len &&
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(
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data[pos] !== needle[0] ||
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(
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(Buffer.compare(
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data.subarray(pos, pos + len - pos),
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needle.subarray(0, len - pos)
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) !== 0)
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)
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)
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) {
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++pos
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}
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if (pos < len) {
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data.copy(this._lookbehind, 0, pos, pos + (len - pos))
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this._lookbehind_size = len - pos
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}
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// Everything until pos is guaranteed not to contain needle data.
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if (pos > 0) { this.emit('info', false, data, this._bufpos, pos < len ? pos : len) }
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this._bufpos = len
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return len
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}
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SBMH.prototype._sbmh_lookup_char = function (data, pos) {
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return (pos < 0)
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? this._lookbehind[this._lookbehind_size + pos]
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: data[pos]
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}
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SBMH.prototype._sbmh_memcmp = function (data, pos, len) {
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for (var i = 0; i < len; ++i) { // eslint-disable-line no-var
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if (this._sbmh_lookup_char(data, pos + i) !== this._needle[i]) { return false }
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}
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return true
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}
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module.exports = SBMH
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