#define NULL ((void *)0)
typedef unsigned long size_t; // Customize by platform.
typedef long intptr_t;
typedef unsigned long uintptr_t;
typedef long scalar_t__; // Either arithmetic or pointer type.
/* By default, we understand bool (as a convenience). */
typedef int bool;
#define false 0
#define true 1

/* Forward declarations */

/* Type definitions */
typedef int uint32_t;

/* Variables and functions */
int CountBits32(uint32_t val) {
  val = (val & 0x55555555) + ((val & 0xaaaaaaaa) >> 1);
  val = (val & 0x33333333) + ((val & 0xcccccccc) >> 2);
  val = (val & 0x0f0f0f0f) + ((val & 0xf0f0f0f0) >> 4);
  val = (val & 0x00ff00ff) + ((val & 0xff00ff00) >> 8);
  val = (val & 0x0000ffff) + ((val & 0xffff0000) >> 16);
  return val;
}


x86 assembly (clang, -O0):
<CountBits32>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0x4(%rbp)
mov    -0x4(%rbp),%eax
and    $0x55555555,%eax
mov    -0x4(%rbp),%ecx
and    $0xaaaaaaaa,%ecx
shr    $0x1,%ecx
add    %ecx,%eax
mov    %eax,-0x4(%rbp)
mov    -0x4(%rbp),%eax
and    $0x33333333,%eax
mov    -0x4(%rbp),%ecx
and    $0xcccccccc,%ecx
shr    $0x2,%ecx
add    %ecx,%eax
mov    %eax,-0x4(%rbp)
mov    -0x4(%rbp),%eax
and    $0xf0f0f0f,%eax
mov    -0x4(%rbp),%ecx
and    $0xf0f0f0f0,%ecx
shr    $0x4,%ecx
add    %ecx,%eax
mov    %eax,-0x4(%rbp)
mov    -0x4(%rbp),%eax
and    $0xff00ff,%eax
mov    -0x4(%rbp),%ecx
and    $0xff00ff00,%ecx
shr    $0x8,%ecx
add    %ecx,%eax
mov    %eax,-0x4(%rbp)
mov    -0x4(%rbp),%eax
and    $0xffff,%eax
mov    -0x4(%rbp),%ecx
and    $0xffff0000,%ecx
shr    $0x10,%ecx
add    %ecx,%eax
mov    %eax,-0x4(%rbp)
mov    -0x4(%rbp),%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<CountBits32>:
mov    %edi,%eax
and    $0x55555555,%eax
shr    %edi
and    $0x55555555,%edi
add    %edi,%eax
mov    %eax,%ecx
and    $0x33333333,%ecx
shr    $0x2,%eax
and    $0x33333333,%eax
add    %ecx,%eax
mov    %eax,%ecx
and    $0x7070707,%ecx
shr    $0x4,%eax
and    $0x7070707,%eax
add    %ecx,%eax
mov    %eax,%ecx
and    $0xf000f,%ecx
shr    $0x8,%eax
and    $0xf000f,%eax
add    %ecx,%eax
movzwl %ax,%ecx
shr    $0x10,%eax
add    %ecx,%eax
ret

LLVM IR (-O0):
define i32 @CountBits32(i32 %0) {
%2 = alloca i32
store i32 %0, i32* %2
%3 = load i32, i32* %2
%4 = and i32 %3, 1431655765
%5 = load i32, i32* %2
%6 = and i32 %5, -1431655766
%7 = lshr i32 %6, 1
%8 = add i32 %4, %7
store i32 %8, i32* %2
%9 = load i32, i32* %2
%10 = and i32 %9, 858993459
%11 = load i32, i32* %2
%12 = and i32 %11, -858993460
%13 = lshr i32 %12, 2
%14 = add i32 %10, %13
store i32 %14, i32* %2
%15 = load i32, i32* %2
%16 = and i32 %15, 252645135
%17 = load i32, i32* %2
%18 = and i32 %17, -252645136
%19 = lshr i32 %18, 4
%20 = add i32 %16, %19
store i32 %20, i32* %2
%21 = load i32, i32* %2
%22 = and i32 %21, 16711935
%23 = load i32, i32* %2
%24 = and i32 %23, -16711936
%25 = lshr i32 %24, 8
%26 = add i32 %22, %25
store i32 %26, i32* %2
%27 = load i32, i32* %2
%28 = and i32 %27, 65535
%29 = load i32, i32* %2
%30 = and i32 %29, -65536
%31 = lshr i32 %30, 16
%32 = add i32 %28, %31
store i32 %32, i32* %2
%33 = load i32, i32* %2
ret i32 %33
}

LLVM IR (-O2):
define i32 @CountBits32(i32 %0) {
%2 = and i32 %0, 1431655765
%3 = lshr i32 %0, 1
%4 = and i32 %3, 1431655765
%5 = add nuw i32 %4, %2
%6 = and i32 %5, 858993459
%7 = lshr i32 %5, 2
%8 = and i32 %7, 858993459
%9 = add nuw nsw i32 %8, %6
%10 = and i32 %9, 117901063
%11 = lshr i32 %9, 4
%12 = and i32 %11, 117901063
%13 = add nuw nsw i32 %12, %10
%14 = and i32 %13, 983055
%15 = lshr i32 %13, 8
%16 = and i32 %15, 983055
%17 = add nuw nsw i32 %16, %14
%18 = and i32 %17, 31
%19 = lshr i32 %17, 16
%20 = add nuw nsw i32 %18, %19
ret i32 %20
}