327 lines
11 KiB
JavaScript
327 lines
11 KiB
JavaScript
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'use strict';
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// See state defs from inflate.js
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var BAD = 30; /* got a data error -- remain here until reset */
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var TYPE = 12; /* i: waiting for type bits, including last-flag bit */
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/*
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Decode literal, length, and distance codes and write out the resulting
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literal and match bytes until either not enough input or output is
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available, an end-of-block is encountered, or a data error is encountered.
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When large enough input and output buffers are supplied to inflate(), for
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example, a 16K input buffer and a 64K output buffer, more than 95% of the
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inflate execution time is spent in this routine.
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Entry assumptions:
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state.mode === LEN
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strm.avail_in >= 6
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strm.avail_out >= 258
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start >= strm.avail_out
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state.bits < 8
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On return, state.mode is one of:
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LEN -- ran out of enough output space or enough available input
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TYPE -- reached end of block code, inflate() to interpret next block
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BAD -- error in block data
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Notes:
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- The maximum input bits used by a length/distance pair is 15 bits for the
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length code, 5 bits for the length extra, 15 bits for the distance code,
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and 13 bits for the distance extra. This totals 48 bits, or six bytes.
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Therefore if strm.avail_in >= 6, then there is enough input to avoid
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checking for available input while decoding.
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- The maximum bytes that a single length/distance pair can output is 258
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bytes, which is the maximum length that can be coded. inflate_fast()
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requires strm.avail_out >= 258 for each loop to avoid checking for
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output space.
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*/
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module.exports = function inflate_fast(strm, start) {
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var state;
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var _in; /* local strm.input */
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var last; /* have enough input while in < last */
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var _out; /* local strm.output */
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var beg; /* inflate()'s initial strm.output */
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var end; /* while out < end, enough space available */
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//#ifdef INFLATE_STRICT
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var dmax; /* maximum distance from zlib header */
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//#endif
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var wsize; /* window size or zero if not using window */
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var whave; /* valid bytes in the window */
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var wnext; /* window write index */
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// Use `s_window` instead `window`, avoid conflict with instrumentation tools
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var s_window; /* allocated sliding window, if wsize != 0 */
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var hold; /* local strm.hold */
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var bits; /* local strm.bits */
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var lcode; /* local strm.lencode */
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var dcode; /* local strm.distcode */
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var lmask; /* mask for first level of length codes */
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var dmask; /* mask for first level of distance codes */
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var here; /* retrieved table entry */
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var op; /* code bits, operation, extra bits, or */
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/* window position, window bytes to copy */
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var len; /* match length, unused bytes */
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var dist; /* match distance */
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var from; /* where to copy match from */
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var from_source;
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var input, output; // JS specific, because we have no pointers
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/* copy state to local variables */
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state = strm.state;
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//here = state.here;
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_in = strm.next_in;
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input = strm.input;
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last = _in + (strm.avail_in - 5);
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_out = strm.next_out;
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output = strm.output;
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beg = _out - (start - strm.avail_out);
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end = _out + (strm.avail_out - 257);
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//#ifdef INFLATE_STRICT
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dmax = state.dmax;
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//#endif
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wsize = state.wsize;
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whave = state.whave;
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wnext = state.wnext;
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s_window = state.window;
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hold = state.hold;
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bits = state.bits;
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lcode = state.lencode;
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dcode = state.distcode;
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lmask = (1 << state.lenbits) - 1;
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dmask = (1 << state.distbits) - 1;
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/* decode literals and length/distances until end-of-block or not enough
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input data or output space */
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top:
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do {
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if (bits < 15) {
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hold += input[_in++] << bits;
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bits += 8;
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hold += input[_in++] << bits;
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bits += 8;
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}
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here = lcode[hold & lmask];
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dolen:
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for (;;) { // Goto emulation
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op = here >>> 24/*here.bits*/;
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hold >>>= op;
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bits -= op;
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op = (here >>> 16) & 0xff/*here.op*/;
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if (op === 0) { /* literal */
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//Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ?
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// "inflate: literal '%c'\n" :
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// "inflate: literal 0x%02x\n", here.val));
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output[_out++] = here & 0xffff/*here.val*/;
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}
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else if (op & 16) { /* length base */
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len = here & 0xffff/*here.val*/;
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op &= 15; /* number of extra bits */
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if (op) {
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if (bits < op) {
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hold += input[_in++] << bits;
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bits += 8;
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}
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len += hold & ((1 << op) - 1);
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hold >>>= op;
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bits -= op;
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}
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//Tracevv((stderr, "inflate: length %u\n", len));
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if (bits < 15) {
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hold += input[_in++] << bits;
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bits += 8;
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hold += input[_in++] << bits;
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bits += 8;
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}
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here = dcode[hold & dmask];
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dodist:
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for (;;) { // goto emulation
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op = here >>> 24/*here.bits*/;
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hold >>>= op;
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bits -= op;
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op = (here >>> 16) & 0xff/*here.op*/;
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if (op & 16) { /* distance base */
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dist = here & 0xffff/*here.val*/;
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op &= 15; /* number of extra bits */
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if (bits < op) {
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hold += input[_in++] << bits;
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bits += 8;
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if (bits < op) {
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hold += input[_in++] << bits;
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bits += 8;
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}
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}
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dist += hold & ((1 << op) - 1);
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//#ifdef INFLATE_STRICT
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if (dist > dmax) {
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strm.msg = 'invalid distance too far back';
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state.mode = BAD;
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break top;
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}
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//#endif
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hold >>>= op;
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bits -= op;
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//Tracevv((stderr, "inflate: distance %u\n", dist));
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op = _out - beg; /* max distance in output */
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if (dist > op) { /* see if copy from window */
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op = dist - op; /* distance back in window */
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if (op > whave) {
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if (state.sane) {
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strm.msg = 'invalid distance too far back';
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state.mode = BAD;
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break top;
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}
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// (!) This block is disabled in zlib defailts,
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// don't enable it for binary compatibility
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//#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
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// if (len <= op - whave) {
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// do {
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// output[_out++] = 0;
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// } while (--len);
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// continue top;
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// }
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// len -= op - whave;
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// do {
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// output[_out++] = 0;
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// } while (--op > whave);
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// if (op === 0) {
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// from = _out - dist;
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// do {
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// output[_out++] = output[from++];
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// } while (--len);
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// continue top;
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// }
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//#endif
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}
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from = 0; // window index
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from_source = s_window;
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if (wnext === 0) { /* very common case */
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from += wsize - op;
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if (op < len) { /* some from window */
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len -= op;
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do {
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output[_out++] = s_window[from++];
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} while (--op);
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from = _out - dist; /* rest from output */
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from_source = output;
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}
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}
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else if (wnext < op) { /* wrap around window */
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from += wsize + wnext - op;
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op -= wnext;
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if (op < len) { /* some from end of window */
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len -= op;
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do {
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output[_out++] = s_window[from++];
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} while (--op);
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from = 0;
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if (wnext < len) { /* some from start of window */
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op = wnext;
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len -= op;
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do {
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output[_out++] = s_window[from++];
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} while (--op);
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from = _out - dist; /* rest from output */
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from_source = output;
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}
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}
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}
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else { /* contiguous in window */
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from += wnext - op;
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if (op < len) { /* some from window */
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len -= op;
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do {
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output[_out++] = s_window[from++];
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} while (--op);
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from = _out - dist; /* rest from output */
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from_source = output;
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}
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}
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while (len > 2) {
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output[_out++] = from_source[from++];
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output[_out++] = from_source[from++];
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output[_out++] = from_source[from++];
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len -= 3;
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}
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if (len) {
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output[_out++] = from_source[from++];
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if (len > 1) {
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output[_out++] = from_source[from++];
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}
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}
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}
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else {
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from = _out - dist; /* copy direct from output */
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do { /* minimum length is three */
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output[_out++] = output[from++];
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output[_out++] = output[from++];
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output[_out++] = output[from++];
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len -= 3;
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} while (len > 2);
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if (len) {
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output[_out++] = output[from++];
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if (len > 1) {
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output[_out++] = output[from++];
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}
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}
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}
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}
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else if ((op & 64) === 0) { /* 2nd level distance code */
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here = dcode[(here & 0xffff)/*here.val*/ + (hold & ((1 << op) - 1))];
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continue dodist;
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}
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else {
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strm.msg = 'invalid distance code';
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state.mode = BAD;
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break top;
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}
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break; // need to emulate goto via "continue"
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}
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}
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else if ((op & 64) === 0) { /* 2nd level length code */
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here = lcode[(here & 0xffff)/*here.val*/ + (hold & ((1 << op) - 1))];
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continue dolen;
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}
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else if (op & 32) { /* end-of-block */
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//Tracevv((stderr, "inflate: end of block\n"));
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state.mode = TYPE;
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break top;
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}
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else {
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strm.msg = 'invalid literal/length code';
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state.mode = BAD;
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break top;
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}
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break; // need to emulate goto via "continue"
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}
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} while (_in < last && _out < end);
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/* return unused bytes (on entry, bits < 8, so in won't go too far back) */
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len = bits >> 3;
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_in -= len;
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bits -= len << 3;
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hold &= (1 << bits) - 1;
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/* update state and return */
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strm.next_in = _in;
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strm.next_out = _out;
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strm.avail_in = (_in < last ? 5 + (last - _in) : 5 - (_in - last));
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strm.avail_out = (_out < end ? 257 + (end - _out) : 257 - (_out - end));
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state.hold = hold;
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state.bits = bits;
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return;
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};
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