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, 45 insertions, 0 deletions

diff --git a/sysdeps/ieee754/flt-32/e_ilogbf.c b/sysdeps/ieee754/flt-32/e_ilogbf.c
new file mode 100644
index 0000000000..c7441a8561
--- /dev/null
+++ b/sysdeps/ieee754/flt-32/e_ilogbf.c
@@ -0,0 +1,45 @@
+/* s_ilogbf.c -- float version of s_ilogb.c.
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
+ */
+
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+#if defined(LIBM_SCCS) && !defined(lint)
+static char rcsid[] = "$NetBSD: s_ilogbf.c,v 1.4 1995/05/10 20:47:31 jtc Exp $";
+#endif
+
+#include <limits.h>
+#include <math.h>
+#include <math_private.h>
+
+int __ieee754_ilogbf(float x)
+{
+	int32_t hx,ix;
+
+	GET_FLOAT_WORD(hx,x);
+	hx &= 0x7fffffff;
+	if(hx<0x00800000) {
+	    if(hx==0)
+		return FP_ILOGB0;	/* ilogb(0) = FP_ILOGB0 */
+	    else			/* subnormal x */
+	        for (ix = -126,hx<<=8; hx>0; hx<<=1) ix -=1;
+	    return ix;
+	}
+	else if (hx<0x7f800000) return (hx>>23)-127;
+	else if (FP_ILOGBNAN != INT_MAX) {
+	    /* ISO C99 requires ilogbf(+-Inf) == INT_MAX.  */
+	    if (hx==0x7f800000)
+		return INT_MAX;
+	}
+	return FP_ILOGBNAN;
+}
+strong_alias (__ieee754_ilogbf, __ilogbf_finite)