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71 lines
1.7 KiB
C
71 lines
1.7 KiB
C
/*
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LZG decompression library.
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See lzh.h and https://liblzg.bitsnbites.eu/
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*/
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#include <string.h>
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const unsigned char LZG_LENGTH_DECODE_LUT[32] = {
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2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,
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18,19,20,21,22,23,24,25,26,27,28,29,35,48,72,128
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};
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#pragma codesize (200) // make code faster?
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unsigned char* lzg_decode_vram(const unsigned char* _src,
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unsigned char* _dest,
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unsigned char* _end) {
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// copy params to static locals
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register const unsigned char* src = _src;
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register unsigned char* dest = _dest;
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unsigned char* end = _end;
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// more locals
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char marker[4];
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unsigned int length, offset;
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unsigned char sym, b, b2;
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// copy 4 marker bytes to locals
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memcpy(marker, src, 4);
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src += 4;
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// loop until we run out of buffer space
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while (dest < end) {
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sym = src[0];
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b = src[1];
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src += 2;
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// copy commands
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offset = 0;
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b2 = b & 0x1f;
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length = LZG_LENGTH_DECODE_LUT[b2]; // required for aaaa,y
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// look for marker symbols
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if (sym == marker[0]) {
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if (b == 0) goto literal;
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b2 = *src++;
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offset = ((b2 << 8) | *src++) + 2056; // 16-bit value
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} else if (sym == marker[1]) {
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if (b == 0) goto literal;
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b2 = *src++;
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offset = (((b & 0xe0) << 3) | b2) + 8;
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} else if (sym == marker[2]) {
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length = (b >> 6) + 3;
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offset = (b & 0x3f) + 8;
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} else if (sym == marker[3]) {
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offset = (b >> 5) + 1;
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} else {
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src--;
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literal:
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*dest++ = sym;
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continue;
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}
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// escape marker symbol
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if (b == 0) goto literal;
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// check for dest. overflow
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if (dest + length > end) {
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length = end - dest;
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}
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// copy bytes
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memcpy(dest, dest - offset, length);
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dest += length;
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}
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return dest;
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}
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