library/cpp/on_disk/chunks/reader.cpp


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#include <util/generic/cast.h>
#include <util/memory/blob.h> 
#include <util/system/unaligned_mem.h>
 
#include "reader.h" 
 
template <typename T> 
static inline void ReadAux(const char* data, T* aux, T count, TVector<const char*>* result) {
    result->resize(count); 
    for (size_t i = 0; i < count; ++i) { 
        (*result)[i] = data + ReadUnaligned<T>(aux + i);
    } 
} 
 
TChunkedDataReader::TChunkedDataReader(const TBlob& blob) {
    const char* cdata = blob.AsCharPtr(); 
    const size_t size = blob.Size(); 
    Y_ENSURE(size >= sizeof(ui32), "Empty file with chunks. ");

    ui32 last = ReadUnaligned<ui32>((ui32*)(cdata + size) - 1);
 
    if (last != 0) { // old version file 
        ui32* aux = (ui32*)(cdata + size); 
        ui32 count = last; 
        Size = size - (count + 1) * sizeof(ui32); 
 
        aux -= (count + 1); 
        ReadAux<ui32>(cdata, aux, count, &Offsets); 
        return; 
    } 
 
    Y_ENSURE(size >= 3 * sizeof(ui64), "Blob size must be >= 3 * sizeof(ui64). ");

    ui64* aux = (ui64*)(cdata + size); 
    Version = ReadUnaligned<ui64>(aux - 2);
    Y_ENSURE(Version > 0, "Invalid chunked array version. ");
 
    ui64 count = ReadUnaligned<ui64>(aux - 3);
 
    aux -= (count + 3); 
    ReadAux<ui64>(cdata, aux, count, &Offsets); 
 
    aux -= count; 
    Lengths.resize(count); 
    for (size_t i = 0; i < count; ++i) { 
        Lengths[i] = IntegerCast<size_t>(ReadUnaligned<ui64>(aux + i));
    } 
} 
 
TBlob TChunkedDataReader::GetBlob(size_t index) const {
    return TBlob::NoCopy(GetBlock(index), GetBlockLen(index));
}