xref: /illumos-gate/usr/src/lib/libm/common/C/ilogb.c (revision 862246c1)
125c28e83SPiotr Jasiukajtis /*
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2125c28e83SPiotr Jasiukajtis 
2225c28e83SPiotr Jasiukajtis /*
2325c28e83SPiotr Jasiukajtis  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
2425c28e83SPiotr Jasiukajtis  */
2525c28e83SPiotr Jasiukajtis /*
2625c28e83SPiotr Jasiukajtis  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
2725c28e83SPiotr Jasiukajtis  * Use is subject to license terms.
2825c28e83SPiotr Jasiukajtis  */
2925c28e83SPiotr Jasiukajtis 
30ddc0e0b5SRichard Lowe #pragma weak __ilogb = ilogb
3125c28e83SPiotr Jasiukajtis 
3225c28e83SPiotr Jasiukajtis #include "libm.h"
3325c28e83SPiotr Jasiukajtis #include "xpg6.h"	/* __xpg6 */
3425c28e83SPiotr Jasiukajtis 
351ec68d33SRichard Lowe #if defined(__x86)
3625c28e83SPiotr Jasiukajtis static const double two52 = 4503599627370496.0;
3725c28e83SPiotr Jasiukajtis #else
3825c28e83SPiotr Jasiukajtis /*
3925c28e83SPiotr Jasiukajtis  * v: high part of a non-zero subnormal |x|; w: low part of |x|
4025c28e83SPiotr Jasiukajtis  */
4125c28e83SPiotr Jasiukajtis static int
ilogb_subnormal(unsigned v,unsigned w)4225c28e83SPiotr Jasiukajtis ilogb_subnormal(unsigned v, unsigned w) {
4325c28e83SPiotr Jasiukajtis 	int r = -1022 - 52;
4425c28e83SPiotr Jasiukajtis 
4525c28e83SPiotr Jasiukajtis 	if (v)
4625c28e83SPiotr Jasiukajtis 		r += 32;
4725c28e83SPiotr Jasiukajtis 	else
4825c28e83SPiotr Jasiukajtis 		v = w;
4925c28e83SPiotr Jasiukajtis 	if (v & 0xffff0000)
5025c28e83SPiotr Jasiukajtis 		r += 16, v >>= 16;
5125c28e83SPiotr Jasiukajtis 	if (v & 0xff00)
5225c28e83SPiotr Jasiukajtis 		r += 8, v >>= 8;
5325c28e83SPiotr Jasiukajtis 	if (v & 0xf0)
5425c28e83SPiotr Jasiukajtis 		r += 4, v >>= 4;
5525c28e83SPiotr Jasiukajtis 	v <<= 1;
5625c28e83SPiotr Jasiukajtis 	return (r + ((0xffffaa50 >> v) & 0x3));
5725c28e83SPiotr Jasiukajtis }
581ec68d33SRichard Lowe #endif	/* defined(__x86) */
5925c28e83SPiotr Jasiukajtis 
6025c28e83SPiotr Jasiukajtis static int
raise_invalid(int v)6125c28e83SPiotr Jasiukajtis raise_invalid(int v) {	/* SUSv3 requires ilogb(0,+/-Inf,NaN) raise invalid */
6225c28e83SPiotr Jasiukajtis #ifndef lint
6325c28e83SPiotr Jasiukajtis 	if ((__xpg6 & _C99SUSv3_ilogb_0InfNaN_raises_invalid) != 0) {
6425c28e83SPiotr Jasiukajtis 		static const double zero = 0.0;
65*862246c1SToomas Soome 		volatile double dummy __unused;
6625c28e83SPiotr Jasiukajtis 
6725c28e83SPiotr Jasiukajtis 		dummy = zero / zero;
6825c28e83SPiotr Jasiukajtis 	}
6925c28e83SPiotr Jasiukajtis #endif
7025c28e83SPiotr Jasiukajtis 	return (v);
7125c28e83SPiotr Jasiukajtis }
7225c28e83SPiotr Jasiukajtis 
7325c28e83SPiotr Jasiukajtis int
ilogb(double x)7425c28e83SPiotr Jasiukajtis ilogb(double x) {
7525c28e83SPiotr Jasiukajtis 	int *px = (int *) &x, k = px[HIWORD] & ~0x80000000;
7625c28e83SPiotr Jasiukajtis 
7725c28e83SPiotr Jasiukajtis 	if (k < 0x00100000) {
7825c28e83SPiotr Jasiukajtis 		if ((px[LOWORD] | k) == 0)
7925c28e83SPiotr Jasiukajtis 			return (raise_invalid(0x80000001));
8025c28e83SPiotr Jasiukajtis 		else {
811ec68d33SRichard Lowe #if defined(__x86)
8225c28e83SPiotr Jasiukajtis 			x *= two52;
8325c28e83SPiotr Jasiukajtis 			return (((px[HIWORD] & 0x7ff00000) >> 20) - 1075);
8425c28e83SPiotr Jasiukajtis #else
8525c28e83SPiotr Jasiukajtis 			return (ilogb_subnormal(k, px[LOWORD]));
8625c28e83SPiotr Jasiukajtis #endif
8725c28e83SPiotr Jasiukajtis 		}
8825c28e83SPiotr Jasiukajtis 	} else if (k < 0x7ff00000)
8925c28e83SPiotr Jasiukajtis 		return ((k >> 20) - 1023);
9025c28e83SPiotr Jasiukajtis 	else
9125c28e83SPiotr Jasiukajtis 		return (raise_invalid(0x7fffffff));
9225c28e83SPiotr Jasiukajtis }