Index: base/crc.h |
diff --git a/base/crc.h b/base/crc.h |
deleted file mode 100644 |
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--- a/base/crc.h |
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-// Copyright 2003-2009 Google Inc. |
-// |
-// Licensed under the Apache License, Version 2.0 (the "License"); |
-// you may not use this file except in compliance with the License. |
-// You may obtain a copy of the License at |
-// |
-// http://www.apache.org/licenses/LICENSE-2.0 |
-// |
-// Unless required by applicable law or agreed to in writing, software |
-// distributed under the License is distributed on an "AS IS" BASIS, |
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
-// See the License for the specific language governing permissions and |
-// limitations under the License. |
-// ======================================================================== |
- |
-#ifndef _CRC_H_ |
-#define _CRC_H_ |
- |
-#include "base/basictypes.h" |
- |
-namespace omaha { |
- |
-// This class implements CRCs (aka Rabin Fingerprints). |
-// Treats the input as a polynomial with coefficients in Z(2), |
-// and finds the remainder when divided by an irreducible polynomial |
-// of the appropriate length. |
-// It handles all CRC sizes from 8 to 128 bits. |
-// The input string is prefixed with a "1" bit, and has "degree" "0" bits |
-// appended to it before the remainder is found. This ensures that |
-// short strings are scrambled somewhat. |
- |
-// A polynomial is represented by the bit pattern formed by its coefficients, |
-// but with the highest order bit not stored. |
-// The highest degree coefficient is stored in the lowest numbered bit |
-// in the the lowest adderessed byte. Thus, in what follows, |
-// the highest degree coeficient that is stored is in the low order bit |
-// of "lo" or "*lo". |
- |
-// Typical usage: |
-// |
-// // prepare to do 32-bit CRCs using the default polynomial. No rolling hash. |
-// scoped_ptr<CRC> crc(CRC::Default(32, 0)); |
-// ... |
-// uint64 lo; // declare a lo,hi pair to hold the CRC |
-// uint64 hi; |
-// crc->Empty(&lo, &hi); // Initialize to CRC of empty string |
-// crc->Extend(&lo, &hi, "hello", 5); // Get CRC of "hello" |
-// ... |
-// |
-// // prepare to use a 32-bit rolling hash over 6 bytes |
-// scoped_ptr<CRC> crc(CRC::Default(32, 6)); |
-// ... |
-// uint64 lo; // declare a lo,hi pair to hold the CRC |
-// uint64 hi; |
-// crc->Empty(&lo, &hi); // Initialize to CRC of empty string |
-// crc->Extend(&lo, &hi, data, 6); // Get CRC of first 6 bytes |
-// for (int i = 6; i != sizeof (data); i++) { |
-// crc->Roll(&lo, &hi, data[i-6], data[i]); // Move window by one byte |
-// // lo,hi is CRC of bytes data[i-5...i] |
-// } |
-// ... |
-// |
- |
-class CRC { |
-public: |
- // Initialize all the tables for CRC's of a given bit length "degree" |
- // using a default polynomial of the given length. |
- // |
- // The argument "roll_length" is used by subsequent calls to |
- // Roll(). |
- // Returns a handle that MUST NOT be destroyed with delete. |
- // The default polynomials are those in POLYS[8...128]. |
- // Handles returned by Default() MUST NOT be deleted. |
- // Identical calls to Default() yield identical handles. |
- static CRC *Default(int degree, size_t roll_length); |
- |
- // Initialize all the tables for CRC's of a given bit length "degree" |
- // using an arbitrary CRC polynomial. |
- // Normally, you would use Default() instead of New()---see above. |
- // |
- // Requires that "lo,hi" contain an irreducible polynomial of degree "degree" |
- // Requires 8 <= degree && degree <= 128 |
- // Any irreducible polynomial of the correct degree will work. |
- // See the POLYS array for suitable irredicible polynomials. |
- // |
- // The argument "roll_length" is used by subsequent calls to |
- // Roll(). |
- // Each call to New() yeilds a pointer to a new object |
- // that may be deallocated with delete. |
- static CRC *New(uint64 lo, uint64 hi, int degree, size_t roll_length); |
- |
- virtual ~CRC(); |
- |
- // Place the CRC of the empty string in "*lo,*hi" |
- virtual void Empty(uint64 *lo, uint64 *hi) const = 0; |
- |
- // If "*lo,*hi" is the CRC of bytestring A, place the CRC of |
- // the bytestring formed from the concatenation of A and the "length" |
- // bytes at "bytes" into "*lo,*hi". |
- virtual void Extend(/*INOUT*/ uint64 *lo, /*INOUT*/ uint64 *hi, |
- const void *bytes, size_t length) const = 0; |
- |
- // Equivalent to Extend(lo, hi, bytes, length) where "bytes" |
- // points to an array of "length" zero bytes. |
- virtual void ExtendByZeroes(/*INOUT*/ uint64 *lo, /*INOUT*/ uint64 *hi, |
- size_t length) const = 0; |
- |
- // If "*lo,*hi" is the CRC of a byte string of length "roll_length" |
- // (which is an argument to New() and Default()) that consists of |
- // byte "o_byte" followed by string S, set "*lo,*hi" to the CRC of |
- // the string that consists of S followed by the byte "i_byte". |
- virtual void Roll(/*INOUT*/ uint64 *lo, /*INOUT*/ uint64 *hi, |
- uint8 o_byte, uint8 i_byte) const = 0; |
- |
- // POLYS[] is an array of valid triples that may be given to New() |
- static const struct Poly { |
- uint64 lo; // first half suitable CRC polynomial |
- uint64 hi; // second half of suitable CRC polynomial |
- int degree; // degree of suitable CRC polynomial |
- } *const POLYS; |
- // It is guaranteed that no two entries in POLYS[] are identical, |
- // that POLYS[i] cnotains a polynomial of degree i for 8 <= i <= 128, |
- // that POLYS[0] and POLYS[1] contains polynomials of degree 32, |
- // that POLYS[2] and POLYS[3] contains polynomials of degree 64, |
- // that POLYS[4] and POLYS[5] contains polynomials of degree 96, and |
- // that POLYS[6] and POLYS[7] contains polynomials of degree 128. |
- |
- static const int N_POLYS; // Number of elements in POLYS array. |
- |
-protected: |
- CRC(); // Clients may not call constructor; |
- // use Default() or New() instead. |
- |
-private: |
- DISALLOW_EVIL_CONSTRUCTORS(CRC); |
-}; |
- |
-} // namespace omaha |
- |
-#endif |