diff options
Diffstat (limited to 'compiler-rt/lib/popcountdi2.c')
| -rw-r--r-- | compiler-rt/lib/popcountdi2.c | 43 |
1 files changed, 22 insertions, 21 deletions
diff --git a/compiler-rt/lib/popcountdi2.c b/compiler-rt/lib/popcountdi2.c index 338bbb3cad4..78b6d88d731 100644 --- a/compiler-rt/lib/popcountdi2.c +++ b/compiler-rt/lib/popcountdi2.c @@ -1,35 +1,36 @@ -//===-- popcountdi2.c - Implement __popcountdi2 ----------------------------===// -// -// The LLVM Compiler Infrastructure -// -// This file is distributed under the University of Illinois Open Source -// License. See LICENSE.TXT for details. -// -//===----------------------------------------------------------------------===// -// -// This file implements __popcountdi2 for the compiler_rt library. -// -//===----------------------------------------------------------------------===// +/* ===-- popcountdi2.c - Implement __popcountdi2 ----------------------------=== + * + * The LLVM Compiler Infrastructure + * + * This file is distributed under the University of Illinois Open Source + * License. See LICENSE.TXT for details. + * + * ===----------------------------------------------------------------------=== + * + * This file implements __popcountdi2 for the compiler_rt library. + * + * ===----------------------------------------------------------------------=== + */ #include "int_lib.h" -// Returns: count of 1 bits +/* Returns: count of 1 bits */ si_int __popcountdi2(di_int a) { du_int x2 = (du_int)a; x2 = x2 - ((x2 >> 1) & 0x5555555555555555uLL); - // Every 2 bits holds the sum of every pair of bits (32) + /* Every 2 bits holds the sum of every pair of bits (32) */ x2 = ((x2 >> 2) & 0x3333333333333333uLL) + (x2 & 0x3333333333333333uLL); - // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (16) + /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (16) */ x2 = (x2 + (x2 >> 4)) & 0x0F0F0F0F0F0F0F0FuLL; - // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (8) + /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (8) */ su_int x = (su_int)(x2 + (x2 >> 32)); - // The lower 32 bits hold four 16 bit sums (5 significant bits). - // Upper 32 bits are garbage + /* The lower 32 bits hold four 16 bit sums (5 significant bits). */ + /* Upper 32 bits are garbage */ x = x + (x >> 16); - // The lower 16 bits hold two 32 bit sums (6 significant bits). - // Upper 16 bits are garbage - return (x + (x >> 8)) & 0x0000007F; // (7 significant bits) + /* The lower 16 bits hold two 32 bit sums (6 significant bits). */ + /* Upper 16 bits are garbage */ + return (x + (x >> 8)) & 0x0000007F; /* (7 significant bits) */ } |
