popcountdi2.c 1.4 KB

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  1. /* ===-- popcountdi2.c - Implement __popcountdi2 ----------------------------===
  2. *
  3. * The LLVM Compiler Infrastructure
  4. *
  5. * This file is dual licensed under the MIT and the University of Illinois Open
  6. * Source Licenses. See LICENSE.TXT for details.
  7. *
  8. * ===----------------------------------------------------------------------===
  9. *
  10. * This file implements __popcountdi2 for the compiler_rt library.
  11. *
  12. * ===----------------------------------------------------------------------===
  13. */
  14. #include "int_lib.h"
  15. /* Returns: count of 1 bits */
  16. COMPILER_RT_ABI si_int
  17. __popcountdi2(di_int a)
  18. {
  19. du_int x2 = (du_int)a;
  20. x2 = x2 - ((x2 >> 1) & 0x5555555555555555uLL);
  21. /* Every 2 bits holds the sum of every pair of bits (32) */
  22. x2 = ((x2 >> 2) & 0x3333333333333333uLL) + (x2 & 0x3333333333333333uLL);
  23. /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (16) */
  24. x2 = (x2 + (x2 >> 4)) & 0x0F0F0F0F0F0F0F0FuLL;
  25. /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (8) */
  26. su_int x = (su_int)(x2 + (x2 >> 32));
  27. /* The lower 32 bits hold four 16 bit sums (5 significant bits). */
  28. /* Upper 32 bits are garbage */
  29. x = x + (x >> 16);
  30. /* The lower 16 bits hold two 32 bit sums (6 significant bits). */
  31. /* Upper 16 bits are garbage */
  32. return (x + (x >> 8)) & 0x0000007F; /* (7 significant bits) */
  33. }