85 lines
1.8 KiB
C++
85 lines
1.8 KiB
C++
/*
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Based on work of Marcus Comstedt
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http://mc.pp.se, http://mc.pp.se/dc/sw.html, http://mc.pp.se/dc/files/scramble.c
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License: Gotta verify
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Adapted by Stefanos Kornilios Mitsis Poiitidis (skmp) for reicast
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*/
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#include "descrambl.h"
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#include "imgread/common.h"
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#include <algorithm>
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#define MAXCHUNK (2048*1024)
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static unsigned int seed;
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static void my_srand(unsigned int n)
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{
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seed = n & 0xffff;
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}
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static unsigned int my_rand()
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{
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seed = (seed * 2109 + 9273) & 0x7fff;
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return (seed + 0xc000) & 0xffff;
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}
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static void load_chunk(u8* &src, unsigned char *ptr, unsigned long sz)
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{
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verify(sz <= MAXCHUNK);
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static int idx[MAXCHUNK / 32];
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/* Convert chunk size to number of slices */
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sz /= 32;
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/* Initialize index table with unity,
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so that each slice gets loaded exactly once */
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for (u32 i = 0; i < sz; i++)
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idx[i] = i;
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for (int i = sz - 1; i >= 0; --i)
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{
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/* Select a replacement index */
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int x = (my_rand() * i) >> 16;
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/* Swap */
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std::swap(idx[i], idx[x]);
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/* Load resulting slice */
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memcpy(ptr + 32 * idx[i], src, 32);
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src += 32;
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}
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}
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static void descrambl_buffer(u8* src, unsigned char *dst, unsigned long filesz)
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{
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unsigned long chunksz;
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my_srand(filesz);
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/* Descramble 2 meg blocks for as long as possible, then
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gradually reduce the window down to 32 bytes (1 slice) */
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for (chunksz = MAXCHUNK; chunksz >= 32; chunksz >>= 1)
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while (filesz >= chunksz)
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{
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load_chunk(src, dst, chunksz);
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filesz -= chunksz;
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dst += chunksz;
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}
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/* Load final incomplete slice */
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if (filesz)
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memcpy(dst, src, filesz);
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}
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void descrambl_file(u32 FAD, u32 file_size, u8* dst) {
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u8* temp_file = new u8[file_size + 2048];
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libGDR_ReadSector(temp_file, FAD, (file_size+2047) / 2048, 2048);
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descrambl_buffer(temp_file, dst, file_size);
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delete[] temp_file;
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}
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