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Diffstat (limited to 'lib/popcountti2.c')
-rw-r--r-- | lib/popcountti2.c | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/lib/popcountti2.c b/lib/popcountti2.c new file mode 100644 index 000000000..9ac052d91 --- /dev/null +++ b/lib/popcountti2.c @@ -0,0 +1,43 @@ +//===-- popcountti2.c - Implement __popcountti2 ----------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements __popcountti2 for the compiler_rt library. +// +//===----------------------------------------------------------------------===// + +#if __x86_64 + +#include "int_lib.h" + +// Returns: count of 1 bits + +si_int +__popcountti2(ti_int a) +{ + tu_int x3 = (tu_int)a; + x3 = x3 - ((x3 >> 1) & (((tu_int)0x5555555555555555uLL << 64) | + 0x5555555555555555uLL)); + // Every 2 bits holds the sum of every pair of bits (64) + x3 = ((x3 >> 2) & (((tu_int)0x3333333333333333uLL << 64) | 0x3333333333333333uLL)) + + (x3 & (((tu_int)0x3333333333333333uLL << 64) | 0x3333333333333333uLL)); + // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (32) + x3 = (x3 + (x3 >> 4)) + & (((tu_int)0x0F0F0F0F0F0F0F0FuLL << 64) | 0x0F0F0F0F0F0F0F0FuLL); + // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (16) + du_int x2 = (du_int)(x3 + (x3 >> 64)); + // Every 8 bits holds the sum of every 8-set of bits (5 significant bits) (8) + su_int x = (su_int)(x2 + (x2 >> 32)); + // Every 8 bits holds the sum of every 8-set of bits (6 significant bits) (4) + x = x + (x >> 16); + // Every 8 bits holds the sum of every 8-set of bits (7 significant bits) (2) + // Upper 16 bits are garbage + return (x + (x >> 8)) & 0xFF; // (8 significant bits) +} + +#endif |