How to enable support for the POPCNT instruction / intrinsic on my computer?

StackOverflow https://stackoverflow.com/questions/13332352

Question

I tried to run the following program in my computer (Fedora 17 32bit). How can I enable my system to support the popcnt instruction for fast population count?

#include <stdio.h>
#include <nmmintrin.h>

int main(void)
{
    int pop = _mm_popcnt_u32(0xf0f0f0f0ULL);
    printf("pop = %d\n", pop);
    return 0;
}

I compiled the program, and run it, but got the following exception:

[xiliu@xiliu tmp]$ gcc -Wall -march=corei7 -m32 -msse4.2 popcnt.c -o popcnt
[xiliu@xiliu tmp]$ ./popcnt 
Illegal instruction (core dumped)

The following is the information of my processor:

[xiliu@xiliu tmp]$ cat /proc/cpuinfo 
processor   : 0
vendor_id   : GenuineIntel
cpu family  : 6
model       : 15
model name  : Intel(R) Pentium(R) Dual  CPU  T2370  @ 1.73GHz
stepping    : 13
microcode   : 0xa4
cpu MHz     : 800.000
cache size  : 1024 KB
physical id : 0
siblings    : 2
core id     : 0
cpu cores   : 2
apicid      : 0
initial apicid  : 0
fdiv_bug    : no
hlt_bug     : no
f00f_bug    : no
coma_bug    : no
fpu     : yes
fpu_exception   : yes
cpuid level : 10
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx lm constant_tsc arch_perfmon pebs bts aperfmperf pni dtes64 monitor ds_cpl est tm2 ssse3 cx16 xtpr pdcm lahf_lm dtherm
bogomips    : 3458.20
clflush size    : 64
cache_alignment : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:

[... repeated for 2nd core ...]
Was it helpful?

Solution

Use __builtin_popcount() instead, It isn't platform specific.

OTHER TIPS

The first CPU to support the POPCNT instruction was Intel's Nehalem. It looks like yours is of the Core line, which is older. Hasturkun's suggestion will work on your system, but will be implemented with multiple instructions instead of a single one.

If you want a portable solution rather than a GCC-specific one, check out Sean Eron Anderson's excellent Bit Twiddling Hacks page, which has highly optimized code for this.

Your CPU does not support POPCNT. (see https://en.wikipedia.org/wiki/SSE4) But you can use this free and open source tool, to detect if it is supported: https://github.com/mgorny/cpuid2cpuflags

It returns for Intel Core i7-3770 for example

CPU_FLAGS_X86: aes avx f16c mmx mmxext pclmul popcnt sse sse2 sse3 sse4_1 sse4_2 ssse3
Licensed under: CC-BY-SA with attribution
Not affiliated with StackOverflow
scroll top