popcountti2.c 1.7 KB

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  1. //===-- popcountti2.c - Implement __popcountti2
  2. //----------------------------===//
  3. //
  4. // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  5. // See https://llvm.org/LICENSE.txt for license information.
  6. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  7. //
  8. //===----------------------------------------------------------------------===//
  9. //
  10. // This file implements __popcountti2 for the compiler_rt library.
  11. //
  12. //===----------------------------------------------------------------------===//
  13. #include "int_lib.h"
  14. #ifdef CRT_HAS_128BIT
  15. // Returns: count of 1 bits
  16. COMPILER_RT_ABI int __popcountti2(ti_int a) {
  17. tu_int x3 = (tu_int)a;
  18. x3 = x3 - ((x3 >> 1) &
  19. (((tu_int)0x5555555555555555uLL << 64) | 0x5555555555555555uLL));
  20. // Every 2 bits holds the sum of every pair of bits (64)
  21. x3 = ((x3 >> 2) &
  22. (((tu_int)0x3333333333333333uLL << 64) | 0x3333333333333333uLL)) +
  23. (x3 & (((tu_int)0x3333333333333333uLL << 64) | 0x3333333333333333uLL));
  24. // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (32)
  25. x3 = (x3 + (x3 >> 4)) &
  26. (((tu_int)0x0F0F0F0F0F0F0F0FuLL << 64) | 0x0F0F0F0F0F0F0F0FuLL);
  27. // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (16)
  28. du_int x2 = (du_int)(x3 + (x3 >> 64));
  29. // Every 8 bits holds the sum of every 8-set of bits (5 significant bits) (8)
  30. su_int x = (su_int)(x2 + (x2 >> 32));
  31. // Every 8 bits holds the sum of every 8-set of bits (6 significant bits) (4)
  32. x = x + (x >> 16);
  33. // Every 8 bits holds the sum of every 8-set of bits (7 significant bits) (2)
  34. //
  35. // Upper 16 bits are garbage
  36. return (x + (x >> 8)) & 0xFF; // (8 significant bits)
  37. }
  38. #endif // CRT_HAS_128BIT