File indexing completed on 2024-11-17 04:55:18

 /*
     SPDX-License-Identifier: MPL-2.0
 */
 
 /* Copyright (c) 2015 Brian R. Bondy. Distributed under the MPL2 license.
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef HASHFN_H_
 #define HASHFN_H_
 
 #include "./base.h"
 
 typedef uint64_t uint64Array[30];
 static int precomputedArraySize = sizeof(uint64Array) / sizeof(uint64_t);
 
 inline uint64_t customPow(uint64Array *precomputedPowers, bool usePrecomputed,
     uint64_t base, int exp) {
   if (usePrecomputed && exp < precomputedArraySize) {
     return (*precomputedPowers)[exp];
   }
 
   // TOOD: Optimization possible here when passed in toSize which is bigger
   // than precomputedArraySize, we can start from the value of the last
   // precomputed value.
   uint64_t result = 1;
   while (exp) {
     if (exp & 1)
       result *= base;
     exp >>= 1;
     base *= base;
   }
   return result;
 }
 
 
 // Functor for a hashing function
 // Implements a Rabin fingerprint hash function
 class HashFn {
  public:
   // Initialize a HashFn with the prime p which is used as the base of the Rabin
   // fingerprint algorithm
   explicit HashFn(int p, bool precompute = true) {
     this->p = p;
     this->precompute = precompute;
     if (precompute) {
       uint64_t result = 1;
       for (int i = 0; i < precomputedArraySize; i++) {
         precomputedPowers[i] = result;
         result *= p;
       }
     }
   }
 
   virtual uint64_t operator()(const char *input, int len,
       unsigned char lastCharCode, uint64_t lastHash);
 
   virtual uint64_t operator()(const char *input, int len);
 
  private:
   int p;
   bool precompute;
   uint64Array precomputedPowers;
 };
 
 #endif  // HASHFN_H_