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WebSVN – planix.SVN – Blame – /os/branches/feature_unix/sys/src/libc/port/frexp.c – Rev 2

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#include <u.h>
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#include <libc.h>
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/*
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 * this is big/little endian non-portable
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 * it gets the endian from the FPdbleword
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 * union in u.h.
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 */
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#define	MASK	0x7ffL
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#define	SHIFT	20
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#define	BIAS	1022L
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#define	SIG	52
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double
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frexp(double d, int *ep)
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{
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	FPdbleword x, a;
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	*ep = 0;
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	/* order matters: only isNaN can operate on NaN */
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	if(isNaN(d) || isInf(d, 0) || d == 0)
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		return d;
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	x.x = d;
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	a.x = fabs(d);
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	if((a.hi >> SHIFT) == 0){	/* normalize subnormal numbers */
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		x.x = (double)(1ULL<<SIG) * d;
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		*ep = -SIG;
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	}
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	*ep += ((x.hi >> SHIFT) & MASK) - BIAS;
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	x.hi &= ~(MASK << SHIFT);
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	x.hi |= BIAS << SHIFT;
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	return x.x;
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}
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double
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ldexp(double d, int deltae)
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{
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	int e, bits;
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	FPdbleword x;
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	ulong z;
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	if(d == 0)
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		return 0;
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	x.x = d;
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	e = (x.hi >> SHIFT) & MASK;
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	if(deltae >= 0 || e+deltae >= 1){	/* no underflow */
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		e += deltae;
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		if(e >= MASK){		/* overflow */
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			if(d < 0)
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				return Inf(-1);
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			return Inf(1);
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		}
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	}else{	/* underflow gracefully */
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		deltae = -deltae;
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		/* need to shift d right deltae */
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		if(e > 1){		/* shift e-1 by exponent manipulation */
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			deltae -= e-1;
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			e = 1;
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		}
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		if(deltae > 0 && e==1){	/* shift 1 by switch from 1.fff to 0.1ff */
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			deltae--;
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			e = 0;
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			x.lo >>= 1;
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			x.lo |= (x.hi&1)<<31;
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			z = x.hi & ((1<<SHIFT)-1);
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			x.hi &= ~((1<<SHIFT)-1);
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			x.hi |= (1<<(SHIFT-1)) | (z>>1);
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		}
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		while(deltae > 0){		/* shift bits down */
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			bits = deltae;
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			if(bits > SHIFT)
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				bits = SHIFT;
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			x.lo >>= bits;
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			x.lo |= (x.hi&((1<<bits)-1)) << (32-bits);
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			z = x.hi & ((1<<SHIFT)-1);
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			x.hi &= ~((1<<SHIFT)-1);
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			x.hi |= z>>bits;
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			deltae -= bits;
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		}
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	}
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	x.hi &= ~(MASK << SHIFT);
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	x.hi |= (long)e << SHIFT;
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	return x.x;
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}
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double
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modf(double d, double *ip)
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{
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	FPdbleword x;
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	int e;
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	x.x = d;
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	e = (x.hi >> SHIFT) & MASK;
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	if(e == MASK){
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		*ip = d;
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		if(x.lo != 0 || (x.hi & 0xfffffL) != 0)	/* NaN */
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			return d;
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		/* ±Inf */
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		x.hi &= 0x80000000L;
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		return x.x;
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	}
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	if(d < 1) {
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		if(d < 0) {
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			x.x = modf(-d, ip);
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			*ip = -*ip;
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			return -x.x;
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		}
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		*ip = 0;
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		return d;
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	}
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	e -= BIAS;
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	if(e <= SHIFT+1) {
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		x.hi &= ~(0x1fffffL >> e);
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		x.lo = 0;
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	} else
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	if(e <= SHIFT+33)
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		x.lo &= ~(0x7fffffffL >> (e-SHIFT-2));
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	*ip = x.x;
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	return d - x.x;
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}