or they can be decoded on the flow during [Sequence Execution].
Literals can be stored uncompressed or compressed using Huffman prefix codes.
-When compressed, an optional tree description can be present,
+When compressed, a tree description may optionally be present,
followed by 1 or 4 streams.
| `Literals_Section_Header` | [`Huffman_Tree_Description`] | [jumpTable] | Stream1 | [Stream2] | [Stream3] | [Stream4] |
`Regenerated_Size = (Literals_Section_Header[0]>>4) + (Literals_Section_Header[1]<<4) + (Literals_Section_Header[2]<<12)`
Only Stream1 is present for these cases.
-Note : it's allowed to represent a short value (for example `13`)
+Note : it's allowed to represent a short value (for example `27`)
using a long format, even if it's less efficient.
__`Size_Format` for `Compressed_Literals_Block` and `Treeless_Literals_Block`__ :
Both `Regenerated_Size` and `Compressed_Size` use 10 bits (0-1023).
`Literals_Section_Header` uses 3 bytes.
- `Size_Format` == 01 : 4 streams.
- Both `Regenerated_Size` and `Compressed_Size` use 10 bits (0-1023).
+ Both `Regenerated_Size` and `Compressed_Size` use 10 bits (6-1023).
`Literals_Section_Header` uses 3 bytes.
- `Size_Format` == 10 : 4 streams.
- Both `Regenerated_Size` and `Compressed_Size` use 14 bits (0-16383).
+ Both `Regenerated_Size` and `Compressed_Size` use 14 bits (6-16383).
`Literals_Section_Header` uses 4 bytes.
- `Size_Format` == 11 : 4 streams.
- Both `Regenerated_Size` and `Compressed_Size` use 18 bits (0-262143).
+ Both `Regenerated_Size` and `Compressed_Size` use 18 bits (6-262143).
`Literals_Section_Header` uses 5 bytes.
Both `Compressed_Size` and `Regenerated_Size` fields follow __little-endian__ convention.
Note: `Compressed_Size` __includes__ the size of the Huffman Tree description
_when_ it is present.
+4 streams is superior to 1 stream in decompression speed,
+by exploiting instruction level parallelism.
+But it's also more expensive,
+costing on average ~7.3 bytes more than the 1 stream mode, mostly from the jump table.
+
+In general, use the 4 streams mode when there are more literals to decode,
+to favor higher decompression speeds.
+Beyond 1KB, the 4 streams mode is compulsory anyway.
+
+Note that a minimum of 6 bytes is required for the 4 streams mode.
+That's a technical minimum, but it's not recommended to employ the 4 streams mode
+for such a small quantity, that would be wasteful.
+A more practical lower bound would be around ~256 bytes.
+
#### Raw Literals Block
The data in Stream1 is `Regenerated_Size` bytes long,
it contains the raw literals data to be used during [Sequence Execution].
case PREFIX(frameParameter_windowTooLarge): return "Frame requires too much memory for decoding";
case PREFIX(corruption_detected): return "Data corruption detected";
case PREFIX(checksum_wrong): return "Restored data doesn't match checksum";
+ case PREFIX(literals_headerWrong): return "Header of Literals' block doesn't respect format specification";
case PREFIX(parameter_unsupported): return "Unsupported parameter";
case PREFIX(parameter_outOfBound): return "Parameter is out of bound";
case PREFIX(init_missing): return "Context should be init first";
unsigned maxSymbolValue, unsigned tableLog);
/** HUF_compress4X_wksp() :
- * Same as HUF_compress2(), but uses externally allocated `workSpace`.
- * `workspace` must be at least as large as HUF_WORKSPACE_SIZE */
+ * Same as HUF_compress2(), but uses externally allocated @workSpace.
+ * @workSpace's size, aka @wkspSize, must be >= HUF_WORKSPACE_SIZE
+ * @srcSize must be >= 6
+ */
#define HUF_WORKSPACE_SIZE ((8 << 10) + 512 /* sorting scratch space */)
#define HUF_WORKSPACE_SIZE_U64 (HUF_WORKSPACE_SIZE / sizeof(U64))
HUF_PUBLIC_API size_t HUF_compress4X_wksp (void* dst, size_t dstCapacity,
#define MIN_SEQUENCES_SIZE 1 /* nbSeq==0 */
#define MIN_CBLOCK_SIZE (1 /*litCSize*/ + 1 /* RLE or RAW */) /* for a non-null block */
+#define MIN_LITERALS_FOR_4_STREAMS 6
typedef enum { set_basic, set_rle, set_compressed, set_repeat } symbolEncodingType_e;
switch(lhSize)
{
case 3: /* 2 - 2 - 10 - 10 */
+ if (!singleStream) assert(srcSize >= MIN_LITERALS_FOR_4_STREAMS);
{ U32 const lhc = hType + ((U32)(!singleStream) << 2) + ((U32)srcSize<<4) + ((U32)cLitSize<<14);
MEM_writeLE24(ostart, lhc);
break;
}
case 4: /* 2 - 2 - 14 - 14 */
+ assert(srcSize >= MIN_LITERALS_FOR_4_STREAMS);
{ U32 const lhc = hType + (2 << 2) + ((U32)srcSize<<4) + ((U32)cLitSize<<18);
MEM_writeLE32(ostart, lhc);
break;
}
case 5: /* 2 - 2 - 18 - 18 */
+ assert(srcSize >= MIN_LITERALS_FOR_4_STREAMS);
{ U32 const lhc = hType + (3 << 2) + ((U32)srcSize<<4) + ((U32)cLitSize<<22);
MEM_writeLE32(ostart, lhc);
ostart[4] = (BYTE)(cLitSize >> 10);
static U64 HUF_DEltX1_set4(BYTE symbol, BYTE nbBits) {
U64 D4;
if (MEM_isLittleEndian()) {
- D4 = (symbol << 8) + nbBits;
+ D4 = (U64)((symbol << 8) + nbBits);
} else {
- D4 = symbol + (nbBits << 8);
+ D4 = (U64)(symbol + (nbBits << 8));
}
+ assert(D4 < (1U << 16));
D4 *= 0x0001000100010001ULL;
return D4;
}
* rankStart[0] is not filled because there are no entries in the table for
* weight 0.
*/
- {
- int n;
- int nextRankStart = 0;
+ { int n;
+ U32 nextRankStart = 0;
int const unroll = 4;
int const nLimit = (int)nbSymbols - unroll + 1;
for (n=0; n<(int)tableLog+1; n++) {
* We can switch based on the length to a different inner loop which is
* optimized for that particular case.
*/
- {
- U32 w;
- int symbol=wksp->rankVal[0];
- int rankStart=0;
+ { U32 w;
+ int symbol = wksp->rankVal[0];
+ int rankStart = 0;
for (w=1; w<tableLog+1; ++w) {
int const symbolCount = wksp->rankVal[w];
int const length = (1 << w) >> 1;
while (p < pEnd)
HUF_DECODE_SYMBOLX1_0(p, bitDPtr);
- return pEnd-pStart;
+ return (size_t)(pEnd-pStart);
}
FORCE_INLINE_TEMPLATE size_t
return dstSize;
}
+/* HUF_decompress4X1_usingDTable_internal_body():
+ * Conditions :
+ * @dstSize >= 6
+ */
FORCE_INLINE_TEMPLATE size_t
HUF_decompress4X1_usingDTable_internal_body(
void* dst, size_t dstSize,
if (length4 > cSrcSize) return ERROR(corruption_detected); /* overflow */
if (opStart4 > oend) return ERROR(corruption_detected); /* overflow */
+ if (dstSize < 6) return ERROR(corruption_detected); /* stream 4-split doesn't work */
CHECK_F( BIT_initDStream(&bitD1, istart1, length1) );
CHECK_F( BIT_initDStream(&bitD2, istart2, length2) );
CHECK_F( BIT_initDStream(&bitD3, istart3, length3) );
const BYTE* const iend = (const BYTE*)cSrc + 6;
BYTE* const oend = (BYTE*)dst + dstSize;
HUF_DecompressAsmArgs args;
- {
- size_t const ret = HUF_DecompressAsmArgs_init(&args, dst, dstSize, cSrc, cSrcSize, DTable);
+ { size_t const ret = HUF_DecompressAsmArgs_init(&args, dst, dstSize, cSrc, cSrcSize, DTable);
FORWARD_IF_ERROR(ret, "Failed to init asm args");
if (ret != 0)
return HUF_decompress4X1_usingDTable_internal_bmi2(dst, dstSize, cSrc, cSrcSize, DTable);
(void)iend;
/* finish bit streams one by one. */
- {
- size_t const segmentSize = (dstSize+3) / 4;
+ { size_t const segmentSize = (dstSize+3) / 4;
BYTE* segmentEnd = (BYTE*)dst;
int i;
for (i = 0; i < 4; ++i) {
/* decoded size */
return dstSize;
}
+
+/* HUF_decompress4X2_usingDTable_internal_body():
+ * Conditions:
+ * @dstSize >= 6
+ */
FORCE_INLINE_TEMPLATE size_t
HUF_decompress4X2_usingDTable_internal_body(
void* dst, size_t dstSize,
DTableDesc const dtd = HUF_getDTableDesc(DTable);
U32 const dtLog = dtd.tableLog;
- if (length4 > cSrcSize) return ERROR(corruption_detected); /* overflow */
- if (opStart4 > oend) return ERROR(corruption_detected); /* overflow */
+ if (length4 > cSrcSize) return ERROR(corruption_detected); /* overflow */
+ if (opStart4 > oend) return ERROR(corruption_detected); /* overflow */
+ if (dstSize < 6) return ERROR(corruption_detected); /* stream 4-split doesn't work */
CHECK_F( BIT_initDStream(&bitD1, istart1, length1) );
CHECK_F( BIT_initDStream(&bitD2, istart2, length2) );
CHECK_F( BIT_initDStream(&bitD3, istart3, length3) );
}
RETURN_ERROR_IF(litSize > 0 && dst == NULL, dstSize_tooSmall, "NULL not handled");
RETURN_ERROR_IF(litSize > ZSTD_BLOCKSIZE_MAX, corruption_detected, "");
+ if (!singleStream)
+ RETURN_ERROR_IF(litSize < MIN_LITERALS_FOR_4_STREAMS, literals_headerWrong,
+ "Not enough literals (%zu) for the 4-streams mode (min %u)",
+ litSize, MIN_LITERALS_FOR_4_STREAMS);
RETURN_ERROR_IF(litCSize + lhSize > srcSize, corruption_detected, "");
RETURN_ERROR_IF(expectedWriteSize < litSize , dstSize_tooSmall, "");
ZSTD_allocateLiteralsBuffer(dctx, dst, dstCapacity, litSize, streaming, expectedWriteSize, 0);
dctx->litBuffer, litSize, istart+lhSize, litCSize,
dctx->HUFptr, ZSTD_DCtx_get_bmi2(dctx));
} else {
+ assert(litSize >= MIN_LITERALS_FOR_4_STREAMS);
hufSuccess = HUF_decompress4X_usingDTable_bmi2(
dctx->litBuffer, litSize, istart+lhSize, litCSize,
dctx->HUFptr, ZSTD_DCtx_get_bmi2(dctx));
for (i = 8; i < n; i += 8) {
MEM_write64(spread + pos + i, sv);
}
- pos += n;
+ assert(n>=0);
+ pos += (size_t)n;
}
}
/* Now we spread those positions across the table.
ZSTD_error_frameParameter_windowTooLarge = 16,
ZSTD_error_corruption_detected = 20,
ZSTD_error_checksum_wrong = 22,
+ ZSTD_error_literals_headerWrong = 24,
ZSTD_error_dictionary_corrupted = 30,
ZSTD_error_dictionary_wrong = 32,
ZSTD_error_dictionaryCreation_failed = 34,
projects / thirdparty / zstd.git / commitdiff
