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, 55 insertions, 0 deletions

diff --git a/sysdeps/ieee754/dbl-64/e_ilogb.c b/sysdeps/ieee754/dbl-64/e_ilogb.c
new file mode 100644
index 0000000000..7772880a1f
--- /dev/null
+++ b/sysdeps/ieee754/dbl-64/e_ilogb.c
@@ -0,0 +1,55 @@
+/* @(#)s_ilogb.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * 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_ilogb.c,v 1.9 1995/05/10 20:47:28 jtc Exp $";
+#endif
+
+/* ilogb(double x)
+ * return the binary exponent of non-zero x
+ * ilogb(0) = FP_ILOGB0
+ * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
+ * ilogb(+-Inf) = INT_MAX (no signal is raised)
+ */
+
+#include <limits.h>
+#include <math.h>
+#include <math_private.h>
+
+int __ieee754_ilogb(double x)
+{
+	int32_t hx,lx,ix;
+
+	GET_HIGH_WORD(hx,x);
+	hx &= 0x7fffffff;
+	if(hx<0x00100000) {
+	    GET_LOW_WORD(lx,x);
+	    if((hx|lx)==0)
+		return FP_ILOGB0;	/* ilogb(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<0x7ff00000) return (hx>>20)-1023;
+	else if (FP_ILOGBNAN != INT_MAX) {
+	    /* ISO C99 requires ilogb(+-Inf) == INT_MAX.  */
+	    GET_LOW_WORD(lx,x);
+	    if(((hx^0x7ff00000)|lx) == 0)
+		return INT_MAX;
+	}
+	return FP_ILOGBNAN;
+}
+strong_alias (__ieee754_ilogb, __ilogb_finite)