Fix ilogb exception and errno (bug 6794)

[BZ #6794]
Following Joseph comments about bug 6794, here is a proposed fix. It turned out
to be a large fix mainly because I had to move some file along to follow libm
files/names conventions.

Basically I have added wrappers (w_ilogb.c, w_ilogbf.c, w_ilogbl.c) that now calls
the symbol '__ieee754_ilogb'. The wrappers checks for '__ieee754_ilogb' output and
set the errno and raise exceptions as expected.

The '__ieee754_ilogb' is implemented in sysdeps. I have moved the 's_ilogb[f|l]' files
to e_ilogb[f|l] and renamed the '__ilogb[f|l]' to '__ieee754_ilogb[f|l]'.

I also found out a bug in i386 and x86-64 assembly coded ilogb implementation where
it raises a FE_DIVBYZERO when argument is '0.0'. I corrected this issue as well.

Finally I added the errno and FE_INVALID tests for 0.0, NaN and +-InF argument. Tested
on i386, x86-64, ppc32 and ppc64.

1 files changed, 40 insertions, 0 deletions

diff --git a/sysdeps/x86_64/fpu/e_ilogbl.S b/sysdeps/x86_64/fpu/e_ilogbl.S
new file mode 100644
index 0000000000..44f92159a8
--- /dev/null
+++ b/sysdeps/x86_64/fpu/e_ilogbl.S
@@ -0,0 +1,40 @@
+/*
+ * Written by J.T. Conklin <jtc@netbsd.org>.
+ * Changes for long double by Ulrich Drepper <drepper@cygnus.com>
+ * Adapted for x86-64 by Andreas Jaeger <aj@suse.de>.
+ * Public domain.
+ */
+
+#include <machine/asm.h>
+
+ENTRY(__ieee754_ilogbl)
+	fldt	8(%rsp)
+/* I added the following ugly construct because ilogb(+-Inf) is
+   required to return INT_MAX in ISO C99.
+   -- jakub@redhat.com.  */
+	fxam			/* Is NaN or +-Inf?  */
+	fstsw   %ax
+	movb    $0x45, %dh
+	andb    %ah, %dh
+	cmpb    $0x05, %dh
+	je      1f		/* Is +-Inf, jump.  */
+	cmpb    $0x40, %dh
+	je      2f		/* Is +-Inf, jump.  */
+
+	fxtract
+	fstp	%st
+
+	fistpl	-4(%rsp)
+	fwait
+	movl	-4(%rsp),%eax
+
+	ret
+
+1:	fstp	%st
+	movl	$0x7fffffff, %eax
+	ret
+2:	fstp	%st
+	movl	$0x80000000, %eax	/* FP_ILOGB0  */
+	ret
+END (__ieee754_ilogbl)
+weak_alias (__ieee754_ilogbl, __ilogbl_finite)