hash_func01.h 1.3 KB

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  1. /* SPDX-License-Identifier: LGPL-2.1
  2. *
  3. * Based on Paul Hsieh's (LGPG 2.1) hash function
  4. * From: http://www.azillionmonkeys.com/qed/hash.html
  5. */
  6. #define get16bits(d) (*((const __u16 *) (d)))
  7. static __always_inline
  8. __u32 SuperFastHash (const char *data, int len, __u32 initval) {
  9. __u32 hash = initval;
  10. __u32 tmp;
  11. int rem;
  12. if (len <= 0 || data == NULL) return 0;
  13. rem = len & 3;
  14. len >>= 2;
  15. /* Main loop */
  16. #pragma clang loop unroll(full)
  17. for (;len > 0; len--) {
  18. hash += get16bits (data);
  19. tmp = (get16bits (data+2) << 11) ^ hash;
  20. hash = (hash << 16) ^ tmp;
  21. data += 2*sizeof (__u16);
  22. hash += hash >> 11;
  23. }
  24. /* Handle end cases */
  25. switch (rem) {
  26. case 3: hash += get16bits (data);
  27. hash ^= hash << 16;
  28. hash ^= ((signed char)data[sizeof (__u16)]) << 18;
  29. hash += hash >> 11;
  30. break;
  31. case 2: hash += get16bits (data);
  32. hash ^= hash << 11;
  33. hash += hash >> 17;
  34. break;
  35. case 1: hash += (signed char)*data;
  36. hash ^= hash << 10;
  37. hash += hash >> 1;
  38. }
  39. /* Force "avalanching" of final 127 bits */
  40. hash ^= hash << 3;
  41. hash += hash >> 5;
  42. hash ^= hash << 4;
  43. hash += hash >> 17;
  44. hash ^= hash << 25;
  45. hash += hash >> 6;
  46. return hash;
  47. }