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, 57 insertions, 0 deletions

diff --git a/sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c b/sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c
new file mode 100644
index 0000000000..55f87ed422
--- /dev/null
+++ b/sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c
@@ -0,0 +1,57 @@
+/* s_ilogbl.c -- long double version of s_ilogb.c.
+ * Conversion to IEEE quad long double by Jakub Jelinek, jj@ultra.linux.cz.
+ */
+
+/*
+ * ====================================================
+ * 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: $";
+#endif
+
+/* ilogbl(long double x)
+ * return the binary exponent of non-zero x
+ * ilogbl(0) = FP_ILOGB0
+ * ilogbl(NaN) = FP_ILOGBNAN (no signal is raised)
+ * ilogbl(+-Inf) = INT_MAX (no signal is raised)
+ */
+
+#include <limits.h>
+#include <math.h>
+#include <math_private.h>
+#include <math_ldbl_opt.h>
+
+int __ieee754_ilogbl(long double x)
+{
+	int64_t hx,lx;
+	int ix;
+
+	GET_LDOUBLE_WORDS64(hx,lx,x);
+	hx &= 0x7fffffffffffffffLL;
+	if(hx <= 0x0010000000000000LL) {
+	    if((hx|(lx&0x7fffffffffffffffLL))==0)
+		return FP_ILOGB0;	/* ilogbl(0) = FP_ILOGB0 */
+	    else			/* subnormal x */
+		if(hx==0) {
+		    for (ix = -1043; lx>0; lx<<=1) ix -=1;
+		} else {
+		    for (ix = -1022, hx<<=11; hx>0; hx<<=1) ix -=1;
+		}
+	    return ix;
+	}
+	else if (hx<0x7ff0000000000000LL) return (hx>>52)-0x3ff;
+	else if (FP_ILOGBNAN != INT_MAX) {
+	    /* ISO C99 requires ilogbl(+-Inf) == INT_MAX.  */
+	    if (((hx^0x7ff0000000000000LL)|lx) == 0)
+		return INT_MAX;
+	}
+	return FP_ILOGBNAN;
+}