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11fdf7f2 TL |
1 | #include <stdio.h> |
2 | ||
3 | #include "ldm.h" | |
4 | ||
5 | /** | |
6 | * This function reads the header at the beginning of src and writes | |
7 | * the compressed and decompressed size to compressedSize and | |
8 | * decompressedSize. | |
9 | * | |
10 | * The header consists of 16 bytes: 8 bytes each in little-endian format | |
11 | * of the compressed size and the decompressed size. | |
12 | */ | |
13 | void LDM_readHeader(const void *src, U64 *compressedSize, | |
14 | U64 *decompressedSize) { | |
15 | const BYTE *ip = (const BYTE *)src; | |
16 | *compressedSize = MEM_readLE64(ip); | |
17 | *decompressedSize = MEM_readLE64(ip + 8); | |
18 | } | |
19 | ||
20 | /** | |
21 | * Writes the 16-byte header (8-bytes each of the compressedSize and | |
22 | * decompressedSize in little-endian format) to memPtr. | |
23 | */ | |
24 | void LDM_writeHeader(void *memPtr, U64 compressedSize, | |
25 | U64 decompressedSize) { | |
26 | MEM_writeLE64(memPtr, compressedSize); | |
27 | MEM_writeLE64((BYTE *)memPtr + 8, decompressedSize); | |
28 | } | |
29 | ||
30 | struct LDM_DCtx { | |
31 | size_t compressedSize; | |
32 | size_t maxDecompressedSize; | |
33 | ||
34 | const BYTE *ibase; /* Base of input */ | |
35 | const BYTE *ip; /* Current input position */ | |
36 | const BYTE *iend; /* End of source */ | |
37 | ||
38 | const BYTE *obase; /* Base of output */ | |
39 | BYTE *op; /* Current output position */ | |
40 | const BYTE *oend; /* End of output */ | |
41 | }; | |
42 | ||
43 | void LDM_initializeDCtx(LDM_DCtx *dctx, | |
44 | const void *src, size_t compressedSize, | |
45 | void *dst, size_t maxDecompressedSize) { | |
46 | dctx->compressedSize = compressedSize; | |
47 | dctx->maxDecompressedSize = maxDecompressedSize; | |
48 | ||
49 | dctx->ibase = src; | |
50 | dctx->ip = (const BYTE *)src; | |
51 | dctx->iend = dctx->ip + dctx->compressedSize; | |
52 | dctx->op = dst; | |
53 | dctx->oend = dctx->op + dctx->maxDecompressedSize; | |
54 | } | |
55 | ||
56 | size_t LDM_decompress(const void *src, size_t compressedSize, | |
57 | void *dst, size_t maxDecompressedSize) { | |
58 | ||
59 | LDM_DCtx dctx; | |
60 | LDM_initializeDCtx(&dctx, src, compressedSize, dst, maxDecompressedSize); | |
61 | ||
62 | while (dctx.ip < dctx.iend) { | |
63 | BYTE *cpy; | |
64 | const BYTE *match; | |
65 | size_t length, offset; | |
66 | ||
67 | /* Get the literal length. */ | |
68 | const unsigned token = *(dctx.ip)++; | |
69 | if ((length = (token >> ML_BITS)) == RUN_MASK) { | |
70 | unsigned s; | |
71 | do { | |
72 | s = *(dctx.ip)++; | |
73 | length += s; | |
74 | } while (s == 255); | |
75 | } | |
76 | ||
77 | /* Copy the literals. */ | |
78 | cpy = dctx.op + length; | |
79 | memcpy(dctx.op, dctx.ip, length); | |
80 | dctx.ip += length; | |
81 | dctx.op = cpy; | |
82 | ||
83 | //TODO: dynamic offset size? | |
84 | /* Encode the offset. */ | |
85 | offset = MEM_read32(dctx.ip); | |
86 | dctx.ip += LDM_OFFSET_SIZE; | |
87 | match = dctx.op - offset; | |
88 | ||
89 | /* Get the match length. */ | |
90 | length = token & ML_MASK; | |
91 | if (length == ML_MASK) { | |
92 | unsigned s; | |
93 | do { | |
94 | s = *(dctx.ip)++; | |
95 | length += s; | |
96 | } while (s == 255); | |
97 | } | |
98 | length += LDM_MIN_MATCH_LENGTH; | |
99 | ||
100 | /* Copy match. */ | |
101 | cpy = dctx.op + length; | |
102 | ||
103 | // TODO: this can be made more efficient. | |
104 | while (match < cpy - offset && dctx.op < dctx.oend) { | |
105 | *(dctx.op)++ = *match++; | |
106 | } | |
107 | } | |
108 | return dctx.op - (BYTE *)dst; | |
109 | } |