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// This module provides routines for encoding a sequence of typed
// entities into a string. The resulting strings can be
// lexicographically compared to yield the same comparison value that
// would have been generated if the encoded items had been compared
// one by one according to their type.
//
// More precisely, suppose:
// 1. string A is generated by encoding the sequence of items [A_1..A_n]
// 2. string B is generated by encoding the sequence of items [B_1..B_n]
// 3. The types match; i.e., for all i: A_i was encoded using
// the same routine as B_i
// Then:
// Comparing A vs. B lexicographically is the same as comparing
// the vectors [A_1..A_n] and [B_1..B_n] lexicographically.
//
// Furthermore, if n < m, the encoding of [A_1..A_n] is a strict prefix of
// [A_1..A_m] (unless m = n+1 and A_m is the empty string encoded with
// WriteTrailingString, in which case the encodings are equal).
//
// This module is often useful when generating multi-part sstable
// keys that have to be ordered in a particular fashion.
#ifndef TENSORFLOW_LIB_STRINGS_ORDERED_CODE_H__
#define TENSORFLOW_LIB_STRINGS_ORDERED_CODE_H__
#include <string>
#include "tensorflow/core/platform/port.h"
namespace tensorflow {
class StringPiece;
namespace strings {
class OrderedCode {
public:
// -------------------------------------------------------------------
// Encoding routines: each one of the following routines append
// one item to "*dest" in an encoding where larger values are
// ordered lexicographically after smaller values.
static void WriteString(string* dest, StringPiece str);
static void WriteNumIncreasing(string* dest, uint64 num);
static void WriteSignedNumIncreasing(string* dest, int64 num);
// -------------------------------------------------------------------
// Decoding routines: these extract an item earlier encoded using
// the corresponding WriteXXX() routines above. The item is read
// from "*src"; "*src" is modified to point past the decoded item;
// and if "result" is non-NULL, "*result" is modified to contain the
// result. In case of string result, the decoded string is appended to
// "*result". Returns true if the next item was read successfully, false
// otherwise.
static bool ReadString(StringPiece* src, string* result);
static bool ReadNumIncreasing(StringPiece* src, uint64* result);
static bool ReadSignedNumIncreasing(StringPiece* src, int64* result);
// Helper for testing: corrupt "*str" by changing the kth item separator
// in the string.
static void TEST_Corrupt(string* str, int k);
// Helper for testing.
// SkipToNextSpecialByte is an internal routine defined in the .cc file
// with the following semantics. Return a pointer to the first byte
// in the range "[start..limit)" whose value is 0 or 255. If no such
// byte exists in the range, returns "limit".
static const char* TEST_SkipToNextSpecialByte(const char* start,
const char* limit);
private:
// This has only static methods, so disallow construction entirely
OrderedCode();
TF_DISALLOW_COPY_AND_ASSIGN(OrderedCode);
};
} // namespace strings
} // namespace tensorflow
#endif // TENSORFLOW_LIB_STRINGS_ORDERED_CODE_H__
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