LZSS Compression: Difference between revisions
→Example C Decompression Function: tried to use this function and it didn't work. oops. fixed.
>Aruki No edit summary |
>Aruki (→Example C Decompression Function: tried to use this function and it didn't work. oops. fixed.) |
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| '''Unused'''; always 0 | | '''Unused'''; always 0 | ||
|- | |||
| 0x4 | |||
| colspan=2 {{unknown|Compressed data starts}} | |||
|} | |} | ||
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If the bit corresponding to the current data chunk is not set, you read one byte group directly from the compressed buffer; simple. | If the bit corresponding to the current data chunk is not set, you read one byte group directly from the compressed buffer; simple. | ||
If the bit is set, then that means you need to read data back from the decompressed buffer, which is where it gets a little more complicated. Read two bytes from the | If the bit is set, then that means you need to read data back from the decompressed buffer, which is where it gets a little more complicated. Read two bytes from the compressed buffer; these tell you exactly how far back in the decompressed buffer to seek, and how many byte groups to read from it. The exact way to utilize them varies depending which mode is set: | ||
{| class="wikitable" | {| class="wikitable" | ||
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== Example C Decompression Function == | == Example C Decompression Function == | ||
< | <syntaxhighlight lang="c" line start="1">bool DecompressLZSS(u8 *src, u32 src_len, u8 *dst, u32 dst_len) | ||
{ | { | ||
u8 *src_end = src + src_len; | |||
u8 *dst_end = dst + dst_len; | |||
// Read compressed buffer header | // Read compressed buffer header | ||
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case 1: | case 1: | ||
count = (bytes[0] >> 4) + 3; | count = (bytes[0] >> 4) + 3; | ||
length = (bytes[0] & 0xF) | bytes[1]; | length = ((bytes[0] & 0xF) << 0x8) | bytes[1]; | ||
break; | break; | ||
case 2: | case 2: | ||
count = (bytes[0] >> 4) + 2; | count = (bytes[0] >> 4) + 2; | ||
length = ((bytes[0] & 0xF) | bytes[1]) << 1; | length = (((bytes[0] & 0xF) << 0x8) | bytes[1]) << 1; | ||
break; | break; | ||
case 3: | case 3: | ||
count = (bytes[0] >> 4) + 1; | count = (bytes[0] >> 4) + 1; | ||
length = ((bytes[0] & 0xF) | bytes[1]) << 2; | length = (((bytes[0] & 0xF) << 0x8) | bytes[1]) << 2; | ||
break; | break; | ||
} | } | ||
// With the count and length calculated, we'll set a pointer to where we want to read back data from: | // With the count and length calculated, we'll set a pointer to where we want to read back data from: | ||
u8 *seek = dst - length; | |||
// count refers to how many byte groups to read back; the size of one byte group varies depending on mode | // count refers to how many byte groups to read back; the size of one byte group varies depending on mode | ||
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// We've finished decompressing; the last thing to do is check that we've reached the end of both buffers, to verify everything has decompressed correctly. | // We've finished decompressing; the last thing to do is check that we've reached the end of both buffers, to verify everything has decompressed correctly. | ||
return ((src == src_end) && (dst == dst_end)); | return ((src == src_end) && (dst == dst_end)); | ||
}</ | }</syntaxhighlight> | ||
[[Category:File Formats]] | [[Category:File Formats]] | ||
[[Category:Donkey Kong Country: Tropical Freeze]] | [[Category:Donkey Kong Country: Tropical Freeze]] | ||