static size_t ZSTDv07_decodeLiteralsBlock()

in lib/legacy/zstd_v07.c [3284:3411]
116 lines of code
31 McCabe index (conditional complexity)

static size_t ZSTDv07_decodeLiteralsBlock(ZSTDv07_DCtx* dctx,
                          const void* src, size_t srcSize)   /* note : srcSize < BLOCKSIZE */
{
    const BYTE* const istart = (const BYTE*) src;

    if (srcSize < MIN_CBLOCK_SIZE) return ERROR(corruption_detected);

    switch((litBlockType_t)(istart[0]>> 6))
    {
    case lbt_huffman:
        {   size_t litSize, litCSize, singleStream=0;
            U32 lhSize = (istart[0] >> 4) & 3;
            if (srcSize < 5) return ERROR(corruption_detected);   /* srcSize >= MIN_CBLOCK_SIZE == 3; here we need up to 5 for lhSize, + cSize (+nbSeq) */
            switch(lhSize)
            {
            case 0: case 1: default:   /* note : default is impossible, since lhSize into [0..3] */
                /* 2 - 2 - 10 - 10 */
                lhSize=3;
                singleStream = istart[0] & 16;
                litSize  = ((istart[0] & 15) << 6) + (istart[1] >> 2);
                litCSize = ((istart[1] &  3) << 8) + istart[2];
                break;
            case 2:
                /* 2 - 2 - 14 - 14 */
                lhSize=4;
                litSize  = ((istart[0] & 15) << 10) + (istart[1] << 2) + (istart[2] >> 6);
                litCSize = ((istart[2] & 63) <<  8) + istart[3];
                break;
            case 3:
                /* 2 - 2 - 18 - 18 */
                lhSize=5;
                litSize  = ((istart[0] & 15) << 14) + (istart[1] << 6) + (istart[2] >> 2);
                litCSize = ((istart[2] &  3) << 16) + (istart[3] << 8) + istart[4];
                break;
            }
            if (litSize > ZSTDv07_BLOCKSIZE_ABSOLUTEMAX) return ERROR(corruption_detected);
            if (litCSize + lhSize > srcSize) return ERROR(corruption_detected);

            if (HUFv07_isError(singleStream ?
                            HUFv07_decompress1X2_DCtx(dctx->hufTable, dctx->litBuffer, litSize, istart+lhSize, litCSize) :
                            HUFv07_decompress4X_hufOnly (dctx->hufTable, dctx->litBuffer, litSize, istart+lhSize, litCSize) ))
                return ERROR(corruption_detected);

            dctx->litPtr = dctx->litBuffer;
            dctx->litSize = litSize;
            dctx->litEntropy = 1;
            memset(dctx->litBuffer + dctx->litSize, 0, WILDCOPY_OVERLENGTH);
            return litCSize + lhSize;
        }
    case lbt_repeat:
        {   size_t litSize, litCSize;
            U32 lhSize = ((istart[0]) >> 4) & 3;
            if (lhSize != 1)  /* only case supported for now : small litSize, single stream */
                return ERROR(corruption_detected);
            if (dctx->litEntropy==0)
                return ERROR(dictionary_corrupted);

            /* 2 - 2 - 10 - 10 */
            lhSize=3;
            litSize  = ((istart[0] & 15) << 6) + (istart[1] >> 2);
            litCSize = ((istart[1] &  3) << 8) + istart[2];
            if (litCSize + lhSize > srcSize) return ERROR(corruption_detected);

            {   size_t const errorCode = HUFv07_decompress1X4_usingDTable(dctx->litBuffer, litSize, istart+lhSize, litCSize, dctx->hufTable);
                if (HUFv07_isError(errorCode)) return ERROR(corruption_detected);
            }
            dctx->litPtr = dctx->litBuffer;
            dctx->litSize = litSize;
            memset(dctx->litBuffer + dctx->litSize, 0, WILDCOPY_OVERLENGTH);
            return litCSize + lhSize;
        }
    case lbt_raw:
        {   size_t litSize;
            U32 lhSize = ((istart[0]) >> 4) & 3;
            switch(lhSize)
            {
            case 0: case 1: default:   /* note : default is impossible, since lhSize into [0..3] */
                lhSize=1;
                litSize = istart[0] & 31;
                break;
            case 2:
                litSize = ((istart[0] & 15) << 8) + istart[1];
                break;
            case 3:
                litSize = ((istart[0] & 15) << 16) + (istart[1] << 8) + istart[2];
                break;
            }

            if (lhSize+litSize+WILDCOPY_OVERLENGTH > srcSize) {  /* risk reading beyond src buffer with wildcopy */
                if (litSize+lhSize > srcSize) return ERROR(corruption_detected);
                memcpy(dctx->litBuffer, istart+lhSize, litSize);
                dctx->litPtr = dctx->litBuffer;
                dctx->litSize = litSize;
                memset(dctx->litBuffer + dctx->litSize, 0, WILDCOPY_OVERLENGTH);
                return lhSize+litSize;
            }
            /* direct reference into compressed stream */
            dctx->litPtr = istart+lhSize;
            dctx->litSize = litSize;
            return lhSize+litSize;
        }
    case lbt_rle:
        {   size_t litSize;
            U32 lhSize = ((istart[0]) >> 4) & 3;
            switch(lhSize)
            {
            case 0: case 1: default:   /* note : default is impossible, since lhSize into [0..3] */
                lhSize = 1;
                litSize = istart[0] & 31;
                break;
            case 2:
                litSize = ((istart[0] & 15) << 8) + istart[1];
                break;
            case 3:
                litSize = ((istart[0] & 15) << 16) + (istart[1] << 8) + istart[2];
                if (srcSize<4) return ERROR(corruption_detected);   /* srcSize >= MIN_CBLOCK_SIZE == 3; here we need lhSize+1 = 4 */
                break;
            }
            if (litSize > ZSTDv07_BLOCKSIZE_ABSOLUTEMAX) return ERROR(corruption_detected);
            memset(dctx->litBuffer, istart[lhSize], litSize + WILDCOPY_OVERLENGTH);
            dctx->litPtr = dctx->litBuffer;
            dctx->litSize = litSize;
            return lhSize+1;
        }
    default:
        return ERROR(corruption_detected);   /* impossible */
    }
}