xref: /illumos-gate/usr/src/lib/libm/common/R/scalbnf.c (revision ddc0e0b5)
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 
30*ddc0e0b5SRichard Lowe #pragma weak __scalbnf = scalbnf
3125c28e83SPiotr Jasiukajtis 
3225c28e83SPiotr Jasiukajtis #include "libm.h"
3325c28e83SPiotr Jasiukajtis #include <float.h>		/* FLT_MAX, FLT_MIN */
3425c28e83SPiotr Jasiukajtis #include <stdlib.h>		/* abs */
3525c28e83SPiotr Jasiukajtis 
3625c28e83SPiotr Jasiukajtis static const float twom25f = 2.98023223876953125e-8F;
371ec68d33SRichard Lowe #if defined(__x86)
3825c28e83SPiotr Jasiukajtis static const float two23f = 8388608.0F;
3925c28e83SPiotr Jasiukajtis #else
4025c28e83SPiotr Jasiukajtis /*
4125c28e83SPiotr Jasiukajtis  * v: a non-zero subnormal |x|; returns [-22, 0]
4225c28e83SPiotr Jasiukajtis  */
4325c28e83SPiotr Jasiukajtis static int
ilogbf_biased(unsigned v)4425c28e83SPiotr Jasiukajtis ilogbf_biased(unsigned v) {
4525c28e83SPiotr Jasiukajtis 	int r = -22;
4625c28e83SPiotr Jasiukajtis 
4725c28e83SPiotr Jasiukajtis 	if (v & 0xffff0000)
4825c28e83SPiotr Jasiukajtis 		r += 16, v >>= 16;
4925c28e83SPiotr Jasiukajtis 	if (v & 0xff00)
5025c28e83SPiotr Jasiukajtis 		r += 8, v >>= 8;
5125c28e83SPiotr Jasiukajtis 	if (v & 0xf0)
5225c28e83SPiotr Jasiukajtis 		r += 4, v >>= 4;
5325c28e83SPiotr Jasiukajtis 	v <<= 1;
5425c28e83SPiotr Jasiukajtis 	return (r + ((0xffffaa50 >> v) & 0x3));
5525c28e83SPiotr Jasiukajtis }
561ec68d33SRichard Lowe #endif	/* defined(__x86) */
5725c28e83SPiotr Jasiukajtis 
5825c28e83SPiotr Jasiukajtis float
scalbnf(float x,int n)5925c28e83SPiotr Jasiukajtis scalbnf(float x, int n) {
6025c28e83SPiotr Jasiukajtis 	int *px = (int *) &x, ix, k;
6125c28e83SPiotr Jasiukajtis 
6225c28e83SPiotr Jasiukajtis 	ix = *px & ~0x80000000;
6325c28e83SPiotr Jasiukajtis 	k = ix >> 23;
6425c28e83SPiotr Jasiukajtis 	if (k == 0xff)
6525c28e83SPiotr Jasiukajtis #if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
6625c28e83SPiotr Jasiukajtis 		return (ix > 0x7f800000 ? x * x : x);
6725c28e83SPiotr Jasiukajtis #else
6825c28e83SPiotr Jasiukajtis 		return (x + x);
6925c28e83SPiotr Jasiukajtis #endif
7025c28e83SPiotr Jasiukajtis 	if (ix == 0 || n == 0)
7125c28e83SPiotr Jasiukajtis 		return (x);
7225c28e83SPiotr Jasiukajtis 	if (k == 0) {
731ec68d33SRichard Lowe #if defined(__x86)
7425c28e83SPiotr Jasiukajtis 		x *= two23f;
7525c28e83SPiotr Jasiukajtis 		k = ((*px & ~0x80000000) >> 23) - 23;
7625c28e83SPiotr Jasiukajtis #else
7725c28e83SPiotr Jasiukajtis 		k = ilogbf_biased(ix);
7825c28e83SPiotr Jasiukajtis 		*px = (*px & 0x80000000) | (ix << (-k + 1));
7925c28e83SPiotr Jasiukajtis #endif
8025c28e83SPiotr Jasiukajtis 	}
8125c28e83SPiotr Jasiukajtis 	if ((unsigned) abs(n) >= 131072)	/* cast to unsigned for -2^31 */
8225c28e83SPiotr Jasiukajtis 		n >>= 1;		/* avoid subsequent integer overflow */
8325c28e83SPiotr Jasiukajtis 	k += n;
8425c28e83SPiotr Jasiukajtis 	if (k > 0xfe)
8525c28e83SPiotr Jasiukajtis 		return (FLT_MAX * copysignf(FLT_MAX, x));
8625c28e83SPiotr Jasiukajtis 	if (k <= -25)
8725c28e83SPiotr Jasiukajtis 		return (FLT_MIN * copysignf(FLT_MIN, x));
8825c28e83SPiotr Jasiukajtis 	if (k > 0) {
8925c28e83SPiotr Jasiukajtis 		*px = (*px & ~0x7f800000) | (k << 23);
9025c28e83SPiotr Jasiukajtis 		return (x);
9125c28e83SPiotr Jasiukajtis 	}
9225c28e83SPiotr Jasiukajtis 	k += 25;
9325c28e83SPiotr Jasiukajtis 	*px = (*px & ~0x7f800000) | (k << 23);
9425c28e83SPiotr Jasiukajtis 	return (x * twom25f);
9525c28e83SPiotr Jasiukajtis }
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