folly::compression::EliasFanoReader

Synopsis

Declared in <folly/compression/elias_fano/EliasFanoCoding.h>

template<
    class Encoder,
    class Instructions = instructions::Default,
    bool kUnchecked = false,
    class SizeT = Encoder::SkipValueType>
class EliasFanoReader;

Description

The reader maintains a current position. It starts positioned before the first element; advance it with next()/skip()/skipTo() or jump to an absolute position or value with jump()/jumpTo(). While valid(), value() returns the current element. Sequential and skip-based access are sub-linear thanks to the encoded skip/forward pointers.

Type Aliases

Name	Description
`EncoderType`	The encoder type whose output this reader consumes.
`SizeType`	The type used for positions and sizes.
`ValueType`	The element value type.

Member Functions

Name	Description
`EliasFanoReader` [constructor]	Constructs a reader over the given compressed list. The reader starts positioned before the first element, so call next() (or skipTo()/jump()) before reading value().
`jump`	Jumps to the element at position n. The reader can be in any state. Returns false if n >= size().
`jumpTo`	Jumps to the first element >= value. The reader can be in any state. Returns false if no such element exists.
`next`	Advances to the next element. Returns false if the end of the list has been reached.
`position`	Returns the zero-based index of the current element. Before the first advance the position is kBeforeFirstPos.
`prepareSkipTo`	Prepare to skip to `value` by prefetching appropriate memory in both the upper and lower bits.
`previous`	Moves to the previous element. Returns false and resets to before the first element if there is no previous element.
`previousValue`	Returns the value immediately preceding the current one without moving the reader. Requires 0 < position() < size().
`reset`	Repositions the reader before the first element.
`size`	Returns the number of elements in the list.
`skip`	Advances by n elements. n = 0 is allowed and has no effect. Returns false if the end of the list is reached. position() + n must be representable by SizeType.
`skipTo`	Skips to the first element >= value whose position is greater or equal to the current position. Requires that value >= value() (or that the reader is positioned before the first element). Returns false if no such element exists. If kCanBeAtValue is false, the requirement above becomes value > value().
`valid`	Whether the reader is positioned on a valid element, i.e. not before the first element and not past the last one.
`value`	Returns the value of the current element. Requires valid().