280 lines
10 KiB
JavaScript
280 lines
10 KiB
JavaScript
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/* zlib-adler32.js -- JavaScript implementation for the zlib adler32.
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Version: 0.2.0
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LastModified: Apr 12 2012
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Copyright (C) 2012 Masanao Izumo <iz@onicos.co.jp>
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API documentation
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==============================================================================
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Usage: adler = ZLIB.adler32(adler, buf, offset, len);
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Update a running Adler-32 checksum with the bytes buf[offset..offset+len-1] and
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return the updated checksum. If buf is null, this function returns the
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required initial value for the checksum.
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An Adler-32 checksum is almost as reliable as a CRC32 but can be computed
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much faster.
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Usage example:
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var adler = ZLIB.adler32(0, null, 0, 0);
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while (read_buffer(buffer, length) != EOF) {
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adler = ZLIB.adler32(adler, buffer, 0, length);
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}
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if (adler != original_adler) error();
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==============================================================================
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Usage: adler = ZLIB.adler32_combine(adler1, adler2, len2);
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Combine two Adler-32 checksums into one. For two sequences of bytes, seq1
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and seq2 with lengths len1 and len2, Adler-32 checksums were calculated for
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each, adler1 and adler2. adler32_combine() returns the Adler-32 checksum of
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seq1 and seq2 concatenated, requiring only adler1, adler2, and len2. Note
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that the z_off_t type (like off_t) is a signed integer. If len2 is
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negative, the result has no meaning or utility.
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*/
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if( typeof ZLIB === 'undefined' ) {
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alert('ZLIB is not defined. SRC zlib.js before zlib-adler32.js')
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}
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(function() {
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/* adler32.c -- compute the Adler-32 checksum of a data stream
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* Copyright (C) 1995-2011 Mark Adler
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* For conditions of distribution and use, see copyright notice in zlib.h
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*/
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var BASE = 65521; /* largest prime smaller than 65536 */
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var NMAX = 5552;
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/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
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/* ========================================================================= */
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function adler32_string(adler, buf, offset, len)
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{
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var sum2;
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var n;
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/* split Adler-32 into component sums */
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sum2 = (adler >>> 16) & 0xffff;
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adler &= 0xffff;
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/* in case user likes doing a byte at a time, keep it fast */
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if (len == 1) {
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adler += buf.charCodeAt(offset) & 0xff;
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if (adler >= BASE)
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adler -= BASE;
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sum2 += adler;
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if (sum2 >= BASE)
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sum2 -= BASE;
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return adler | (sum2 << 16);
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}
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/* initial Adler-32 value (deferred check for len == 1 speed) */
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if (buf === null)
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return 1;
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/* in case short lengths are provided, keep it somewhat fast */
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if (len < 16) {
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while (len--) {
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adler += buf.charCodeAt(offset++) & 0xff;
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sum2 += adler;
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}
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if (adler >= BASE)
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adler -= BASE;
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sum2 %= BASE; /* only added so many BASE's */
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return adler | (sum2 << 16);
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}
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/* do length NMAX blocks -- requires just one modulo operation */
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while (len >= NMAX) {
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len -= NMAX;
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n = NMAX >> 4; /* NMAX is divisible by 16 */
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do {
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/* 16 sums unrolled */
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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} while (--n);
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adler %= BASE;
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sum2 %= BASE;
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}
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/* do remaining bytes (less than NMAX, still just one modulo) */
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if (len) { /* avoid modulos if none remaining */
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while (len >= 16) {
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len -= 16;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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}
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while (len--) {
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adler += buf.charCodeAt(offset++) & 0xff; sum2 += adler;
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}
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adler %= BASE;
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sum2 %= BASE;
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}
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/* return recombined sums */
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return adler | (sum2 << 16);
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}
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/* ========================================================================= */
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function adler32_array(adler, buf, offset, len)
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{
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var sum2;
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var n;
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/* split Adler-32 into component sums */
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sum2 = (adler >>> 16) & 0xffff;
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adler &= 0xffff;
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/* in case user likes doing a byte at a time, keep it fast */
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if (len == 1) {
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adler += buf[offset];
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if (adler >= BASE)
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adler -= BASE;
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sum2 += adler;
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if (sum2 >= BASE)
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sum2 -= BASE;
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return adler | (sum2 << 16);
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}
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/* initial Adler-32 value (deferred check for len == 1 speed) */
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if (buf === null)
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return 1;
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/* in case short lengths are provided, keep it somewhat fast */
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if (len < 16) {
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while (len--) {
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adler += buf[offset++];
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sum2 += adler;
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}
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if (adler >= BASE)
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adler -= BASE;
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sum2 %= BASE; /* only added so many BASE's */
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return adler | (sum2 << 16);
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}
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/* do length NMAX blocks -- requires just one modulo operation */
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while (len >= NMAX) {
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len -= NMAX;
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n = NMAX >> 4; /* NMAX is divisible by 16 */
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do {
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/* 16 sums unrolled */
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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} while (--n);
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adler %= BASE;
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sum2 %= BASE;
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}
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/* do remaining bytes (less than NMAX, still just one modulo) */
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if (len) { /* avoid modulos if none remaining */
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while (len >= 16) {
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len -= 16;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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adler += buf[offset++]; sum2 += adler;
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}
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while (len--) {
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adler += buf[offset++]; sum2 += adler;
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}
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adler %= BASE;
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sum2 %= BASE;
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}
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/* return recombined sums */
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return adler | (sum2 << 16);
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}
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/* ========================================================================= */
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ZLIB.adler32 = function(adler, buf, offset, len)
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{
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if(typeof buf === 'string') {
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return adler32_string(adler, buf, offset, len);
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} else {
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return adler32_array(adler, buf, offset, len);
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}
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};
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ZLIB.adler32_combine = function(adler1, adler2, len2)
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{
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var sum1;
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var sum2;
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var rem;
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/* for negative len, return invalid adler32 as a clue for debugging */
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if (len2 < 0)
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return 0xffffffff;
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/* the derivation of this formula is left as an exercise for the reader */
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len2 %= BASE; /* assumes len2 >= 0 */
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rem = len2;
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sum1 = adler1 & 0xffff;
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sum2 = rem * sum1;
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sum2 %= BASE;
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sum1 += (adler2 & 0xffff) + BASE - 1;
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sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
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if (sum1 >= BASE) sum1 -= BASE;
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if (sum1 >= BASE) sum1 -= BASE;
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if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);
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if (sum2 >= BASE) sum2 -= BASE;
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return sum1 | (sum2 << 16);
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}
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}());
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