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Re: [COMMITTED] tilegx: enable wordsize-64 support for ieee745 dbl-64.


On 12/23/2014 3:47 PM, Chris Metcalf wrote:
On 12/23/2014 3:06 PM, Joseph Myers wrote:
I take it that the ABI on tilegx32 allows the lround alias to llround

No, it doesn't - I missed this possibility.  I assume the best fix is to
provide an lround override in sysdeps/tile/tilegx/tilegx32/s_lround.c
that invokes llround() and then sign-extends the result?

But, why doesn't MIPS itself use this approach?

Thanks for catching this!

Actually, it is, of course, a little trickier than that, since
we have to prevent s_llround.c from setting up the alias for
lround() as well.  But I think it may make sense to use global
conditional logic to do this.  The current users of dbl-64/wordsize-64
are aarch64, alpha, sparc64, and x86_64.  So as far as I know, the
question is whether the forthcoming ILP32 version of aarch64 would
benefit from this hack (probably yes) and whether the existing x32
version of x86_64 would (not clear to me, but plausibly better to clean
up the high bits of the returned value).  If it's OK to just add
ILP32-conditional logic, we can do use the appended diff.

If not, the simplest thing for me to do would be to just add s_lround.c
and s_llround.c in sysdeps/tile/tilegx/tilegx32 that use the default
versions of dbl-64 and not worry about the slight performance
improvement from using the full 64-bit register size.  Or, we could
come up with some way to use a conditional in this code: for example,
just add a random #ifdef, #define it in a tilegx-specific override
of s_llround.c, and #include the standard version explicitly.  But
this runs counter to the glibc rule of avoiding #ifdef.  I'm not sure what
the cleanest path would be if the use of "#ifdef _LP64" isn't OK.

--- a/sysdeps/ieee754/dbl-64/wordsize-64/s_llround.c
+++ b/sysdeps/ieee754/dbl-64/wordsize-64/s_llround.c
@@ -64,16 +64,31 @@ __llround (double x)

 weak_alias (__llround, llround)
 #ifdef NO_LONG_DOUBLE
-strong_alias (__llround, __lroundl)
-weak_alias (__llround, lroundl)
+strong_alias (__llround, __llroundl)
+weak_alias (__llround, llroundl)
 #endif

-/* long has the same width as long long on 64-bit machines.  */
+/* long has the same width as long long on 64-bit machines.
+   If building for ILP32 on a machine with 64-bit registers, however,
+   do an explicit cast on the return value instead.  */
 #undef lround
 #undef __lround
+#ifdef _LP64
 strong_alias (__llround, __lround)
 weak_alias (__llround, lround)
-#ifdef NO_LONG_DOUBLE
-strong_alias (__llround, __llroundl)
-weak_alias (__llround, llroundl)
+# ifdef NO_LONG_DOUBLE
+strong_alias (__llround, __lroundl)
+weak_alias (__llround, lroundl)
+# endif
+#else
+long int
+__lround (double x)
+{
+  return __llround (x);
+}
+weak_alias (__lround, lround)
+# ifdef NO_LONG_DOUBLE
+strong_alias (__lround, __lroundl)
+weak_alias (__lround, lroundl)
+# endif
 #endif

--
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com


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