Undefined reference to __builtin_ctzll

Радослав Йовчев· Aug 13, 2014, 08:36 UTC · lore

Dear GIT community,

I found myself in situation where I had to install GIT on Debian 3.1 sarge. It comes with GCC 3.3.5. I tried to built from source but the libgcc was not providing the ctzll function, thus I decided to put an implementation.

I do not know how to post and do a nice patch (and whether somebody will care), but I guess, for reference I can post my solution. Just appended in compat/strlcpy.c the following:

int __builtin_ctzll (long long x)
{
        int i;
        for (i = 0; i < 8 * sizeof (long long); ++i)
                if (x & ((long long) 1  << i))
                        break;
        return i;
}

I guess that some ifdef macro can be used to detect compiler version or missing __builtin_ctzll.

With best regards and hopes that this can help somebody in similar situation, Radoslav.

Erik Faye-Lund· Aug 13, 2014, 10:15 UTC · re: Радослав Йовчев · lore

Re: Undefined reference to __builtin_ctzll

On Wed, Aug 13, 2014 at 10:36 AM, Радослав Йовчев <radoslav.tm@gmail.com> wrote:

Show 26 quoted lines

> Dear GIT community,
>
>
> I found myself in situation where I had to install GIT on Debian 3.1
> sarge.  It comes with GCC 3.3.5. I tried to built from source but the
> libgcc was not providing the ctzll function, thus I decided to put an
> implementation.
>
>
> I do not know how to post and do a nice patch (and whether somebody
> will care), but I guess, for reference I can post my solution. Just
> appended in compat/strlcpy.c the following:
>
>
> int __builtin_ctzll (long long x)
> {
>         int i;
>         for (i = 0; i < 8 * sizeof (long long); ++i)
>                 if (x & ((long long) 1  << i))
>                         break;
>         return i;
> }
>
>
> I guess that some ifdef macro can be used to detect compiler version
> or missing __builtin_ctzll.

It seems __builtin_ctzll is only available in GCC 3.4.0 and beyond, so I think a better fix is something like this:

diff --git a/ewah/ewok.h b/ewah/ewok.h
index 43adeb5..2700fa3 100644
--- a/ewah/ewok.h
+++ b/ewah/ewok.h
@@ -47,7 +47,7 @@ static inline uint32_t ewah_bit_popcount64(uint64_t x)
  return (x * 0x0101010101010101ULL) >> 56;
 }

-#ifdef __GNUC__
+#if (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ > 3
 #define ewah_bit_ctz64(x) __builtin_ctzll(x)
 #else
 static inline int ewah_bit_ctz64(uint64_t x)