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#include <stdio.h> |
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#include <string.h> |
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|
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#include "rdesktop.h" |
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|
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/* mppc decompression */ |
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/* http://www.faqs.org/rfcs/rfc2118.html */ |
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|
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/* TODO: research the below statements */ |
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|
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/* there exists one or more patents */ |
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/* related to compression algorithms */ |
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|
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/* since we are only decompressing I */ |
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/* think the end-user is safe. */ |
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|
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/* even if that isn't true, aren't you */ |
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/* already paying royalties */ |
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/* through the CAL licenses? */ |
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|
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/* as the rfc states the algorithm seems to */ |
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/* be LZ77 with a sliding buffer */ |
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/* that is empty at init. */ |
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|
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/* as of my limited knowledge these patents */ |
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/* has expired. */ |
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|
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|
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RDPCOMP g_mppc_dict; |
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|
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int |
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mppc_expand(uint8 * data, uint32 clen, uint8 ctype, uint32 * roff, uint32 * rlen) |
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{ |
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int k, walker_len = 0, walker; |
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int i = 0; |
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int next_offset, match_off; |
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int match_len; |
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int old_offset, match_bits; |
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|
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signed char *dict = &(g_mppc_dict.hist); |
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|
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if ((ctype & RDP_MPPC_COMPRESSED) == 0) |
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{ |
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*roff = 0; |
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*rlen = clen; |
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return 0; |
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} |
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|
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if ((ctype & RDP_MPPC_RESET) != 0) |
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{ |
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g_mppc_dict.roff = 0; |
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} |
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|
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if ((ctype & RDP_MPPC_FLUSH) != 0) |
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{ |
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memset(dict, 0, RDP_MPPC_DICT_SIZE); |
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g_mppc_dict.roff = 0; |
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} |
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|
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*roff = 0; |
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*rlen = 0; |
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|
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walker = g_mppc_dict.roff; |
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|
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next_offset = walker; |
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old_offset = next_offset; |
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*roff = old_offset; |
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if (clen == 0) |
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return 0; |
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clen += i; |
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|
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do |
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{ |
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if (walker_len == 0) |
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{ |
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if (i >= clen) |
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break; |
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walker = data[i++] << 24; |
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walker_len = 8; |
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} |
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if (walker >= 0) |
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{ |
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if (walker_len < 8) |
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{ |
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if (i >= clen) |
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{ |
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if (walker != 0) |
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return -1; |
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break; |
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} |
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walker |= (data[i++] & 0xff) << (24 - walker_len); |
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walker_len += 8; |
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} |
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if (next_offset >= RDP_MPPC_DICT_SIZE) |
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return -1; |
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dict[next_offset++] = (((uint32) walker) >> ((uint32) 24)); |
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walker <<= 8; |
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walker_len -= 8; |
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continue; |
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} |
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walker <<= 1; |
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/* fetch next 8-bits */ |
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if (--walker_len == 0) |
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{ |
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if (i >= clen) |
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return -1; |
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walker = data[i++] << 24; |
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walker_len = 8; |
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} |
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/* literal decoding */ |
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if (walker >= 0) |
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{ |
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if (walker_len < 8) |
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{ |
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if (i >= clen) |
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return -1; |
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walker |= (data[i++] & 0xff) << (24 - walker_len); |
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walker_len += 8; |
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} |
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if (next_offset >= RDP_MPPC_DICT_SIZE) |
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return -1; |
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dict[next_offset++] = (uint8) (walker >> 24 | 0x80); |
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walker <<= 8; |
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walker_len -= 8; |
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continue; |
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} |
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|
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/* decode offset */ |
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/* length pair */ |
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walker <<= 1; |
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if (--walker_len < 2) |
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{ |
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if (i >= clen) |
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return -1; |
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walker |= (data[i++] & 0xff) << (24 - walker_len); |
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walker_len += 8; |
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} |
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/* offset decoding where offset len is: |
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-63: 1111 followed by the lower 6 bits of the value |
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64-319: 1110 followed by the lower 8 bits of the value ( value - 64 ) |
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320-8191: 110 followed by the lower 13 bits of the value ( value - 320 ) |
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*/ |
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switch (((uint32) walker) >> ((uint32) 30)) |
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{ |
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case 3: /* - 63 */ |
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if (walker_len < 8) |
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{ |
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if (i >= clen) |
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return -1; |
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walker |= (data[i++] & 0xff) << (24 - walker_len); |
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walker_len += 8; |
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} |
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walker <<= 2; |
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match_off = ((uint32) walker) >> ((uint32) 26); |
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walker <<= 6; |
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walker_len -= 8; |
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break; |
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|
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case 2: /* 64 - 319 */ |
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for (; walker_len < 10; walker_len += 8) |
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{ |
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if (i >= clen) |
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return -1; |
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walker |= (data[i++] & 0xff) << (24 - walker_len); |
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} |
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|
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walker <<= 2; |
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match_off = (((uint32) walker) >> ((uint32) 24)) + 64; |
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walker <<= 8; |
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walker_len -= 10; |
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break; |
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|
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default: /* 320 - 8191 */ |
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for (; walker_len < 14; walker_len += 8) |
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{ |
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if (i >= clen) |
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return -1; |
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walker |= (data[i++] & 0xff) << (24 - walker_len); |
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} |
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|
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match_off = (walker >> 18) + 320; |
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walker <<= 14; |
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walker_len -= 14; |
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break; |
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} |
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if (walker_len == 0) |
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{ |
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if (i >= clen) |
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return -1; |
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walker = data[i++] << 24; |
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walker_len = 8; |
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} |
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|
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/* decode length of match */ |
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match_len = 0; |
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if (walker >= 0) |
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{ /* special case - length of 3 is in bit 0 */ |
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match_len = 3; |
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walker <<= 1; |
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walker_len--; |
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} |
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else |
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{ |
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/* this is how it works len of: |
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4-7: 10 followed by 2 bits of the value |
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8-15: 110 followed by 3 bits of the value |
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16-31: 1110 followed by 4 bits of the value |
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32-63: .... and so forth |
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64-127: |
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128-255: |
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256-511: |
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512-1023: |
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1024-2047: |
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2048-4095: |
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4096-8191: |
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|
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i.e. 4097 is encoded as: 111111111110 000000000001 |
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meaning 4096 + 1... |
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*/ |
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match_bits = 11; /* 11 bits of value at most */ |
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do |
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{ |
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walker <<= 1; |
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if (--walker_len == 0) |
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{ |
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if (i >= clen) |
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return -1; |
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walker = data[i++] << 24; |
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walker_len = 8; |
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} |
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if (walker >= 0) |
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break; |
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if (--match_bits == 0) |
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{ |
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return -1; |
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} |
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} |
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while (1); |
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match_len = 13 - match_bits; |
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walker <<= 1; |
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if (--walker_len < match_len) |
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{ |
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for (; walker_len < match_len; walker_len += 8) |
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{ |
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if (i >= clen) |
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{ |
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return -1; |
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} |
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walker |= (data[i++] & 0xff) << (24 - walker_len); |
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} |
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} |
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|
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match_bits = match_len; |
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match_len = |
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walker >> 32 - match_bits & ~(-1 << match_bits) | 1 << match_bits; |
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walker <<= match_bits; |
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walker_len -= match_bits; |
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} |
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if (next_offset + match_len >= RDP_MPPC_DICT_SIZE) |
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{ |
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return -1; |
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} |
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/* memory areas can overlap - meaning we can't use memXXX functions */ |
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k = next_offset - match_off & (RDP_MPPC_DICT_SIZE - 1); |
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do |
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{ |
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dict[next_offset++] = dict[k++]; |
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} |
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while (--match_len != 0); |
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} |
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while (1); |
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|
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/* store history offset */ |
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g_mppc_dict.roff = next_offset; |
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|
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*roff = old_offset; |
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*rlen = next_offset - old_offset; |
| 278 |
|
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return 0; |
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} |
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