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50 lines
1.7 KiB
TypeScript
50 lines
1.7 KiB
TypeScript
// Loaded from https://deno.land/x/deno_image@v0.0.3/lib/decoders/fast-png/pako/lib/zlib/adler32.js
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// Note: adler32 takes 12% for level 0 and 2% for level 6.
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// It isn't worth it to make additional optimizations as in original.
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// Small size is preferable.
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// (C) 1995-2013 Jean-loup Gailly and Mark Adler
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// (C) 2014-2017 Vitaly Puzrin and Andrey Tupitsin
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//
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// This software is provided 'as-is', without any express or implied
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// warranty. In no event will the authors be held liable for any damages
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// arising from the use of this software.
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//
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// Permission is granted to anyone to use this software for any purpose,
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// including commercial applications, and to alter it and redistribute it
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// freely, subject to the following restrictions:
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//
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// 1. The origin of this software must not be misrepresented; you must not
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// claim that you wrote the original software. If you use this software
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// in a product, an acknowledgment in the product documentation would be
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// appreciated but is not required.
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// 2. Altered source versions must be plainly marked as such, and must not be
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// misrepresented as being the original software.
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// 3. This notice may not be removed or altered from any source distribution.
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export function adler32(adler, buf, len, pos) {
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var s1 = (adler & 0xffff) |0,
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s2 = ((adler >>> 16) & 0xffff) |0,
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n = 0;
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while (len !== 0) {
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// Set limit ~ twice less than 5552, to keep
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// s2 in 31-bits, because we force signed ints.
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// in other case %= will fail.
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n = len > 2000 ? 2000 : len;
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len -= n;
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do {
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s1 = (s1 + buf[pos++]) |0;
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s2 = (s2 + s1) |0;
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} while (--n);
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s1 %= 65521;
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s2 %= 65521;
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}
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return (s1 | (s2 << 16)) |0;
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}
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