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Diffstat (limited to 'lib/popcountsi2.c')
-rw-r--r-- | lib/popcountsi2.c | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/lib/popcountsi2.c b/lib/popcountsi2.c new file mode 100644 index 000000000..68220aef9 --- /dev/null +++ b/lib/popcountsi2.c @@ -0,0 +1,32 @@ +//===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements __popcountsi2 for the compiler_rt library. +// +//===----------------------------------------------------------------------===// + +#include "int_lib.h" + +// Returns: count of 1 bits + +si_int +__popcountsi2(si_int a) +{ + su_int x = (su_int)a; + x = x - ((x >> 1) & 0x55555555); + // Every 2 bits holds the sum of every pair of bits + x = ((x >> 2) & 0x33333333) + (x & 0x33333333); + // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) + x = (x + (x >> 4)) & 0x0F0F0F0F; + // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) + x = (x + (x >> 16)); + // The lower 16 bits hold two 8 bit sums (5 significant bits). + // Upper 16 bits are garbage + return (x + (x >> 8)) & 0x0000003F; // (6 significant bits) +} |