-/* @(#)s_ilogb.c 5.1 93/09/24 */
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
* ====================================================
*/
-#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) = 0x80000001
- * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
+ * return the binary exponent of x
+ * ilogb(+-0) = FP_ILOGB0
+ * ilogb(+-inf) = INT_MAX
+ * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
*/
#include "math.h"
#include "math_private.h"
-#ifdef __STDC__
- int ilogb(double x)
-#else
- int ilogb(x)
- double x;
-#endif
+int ilogb(double x)
{
int32_t hx,lx,ix;
- GET_HIGH_WORD(hx,x);
+ GET_HIGH_WORD(hx, x);
hx &= 0x7fffffff;
- if(hx<0x00100000) {
- GET_LOW_WORD(lx,x);
- if((hx|lx)==0)
- return 0x80000001; /* ilogb(0) = 0x80000001 */
- 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;
+
+ if (hx < 0x00100000) {
+ GET_LOW_WORD(lx, x);
+ if ((hx|lx)==0) /* +-0, ilogb(0) = FP_ILOGB0 */
+ return FP_ILOGB0;
+ /* subnormal x */
+ ix = -1043;
+ if (hx != 0) {
+ ix = -1022;
+ lx = (hx << 11);
}
- return ix;
+ /* each leading zero mantissa bit makes exponent smaller */
+ for (; lx > 0; lx <<= 1)
+ ix--;
+ return ix;
+ }
+
+ if (hx < 0x7ff00000) /* normal x */
+ return (hx>>20) - 1023;
+
+ if (FP_ILOGBNAN != (~0U >> 1)) {
+ GET_LOW_WORD(lx, x);
+ if (hx == 0x7ff00000 && lx == 0) /* +-inf */
+ return ~0U >> 1; /* = INT_MAX */
}
- else if (hx<0x7ff00000) return (hx>>20)-1023;
- else return 0x7fffffff;
+
+ /* NAN. ilogb(NAN) = FP_ILOGBNAN */
+ return FP_ILOGBNAN;
}
+libm_hidden_def(ilogb)