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/* @(#)e_hypotl.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.
* ====================================================
*/
/* __ieee754_hypotl(x,y)
*
* Method :
* If (assume round-to-nearest) z=x*x+y*y
* has error less than sqrtl(2)/2 ulp, than
* sqrtl(z) has error less than 1 ulp (exercise).
*
* So, compute sqrtl(x*x+y*y) with some care as
* follows to get the error below 1 ulp:
*
* Assume x>y>0;
* (if possible, set rounding to round-to-nearest)
* 1. if x > 2y use
* x1*x1+(y*y+(x2*(x+x1))) for x*x+y*y
* where x1 = x with lower 53 bits cleared, x2 = x-x1; else
* 2. if x <= 2y use
* t1*y1+((x-y)*(x-y)+(t1*y2+t2*y))
* where t1 = 2x with lower 53 bits cleared, t2 = 2x-t1,
* y1= y with lower 53 bits chopped, y2 = y-y1.
*
* NOTE: scaling may be necessary if some argument is too
* large or too tiny
*
* Special cases:
* hypotl(x,y) is INF if x or y is +INF or -INF; else
* hypotl(x,y) is NAN if x or y is NAN.
*
* Accuracy:
* hypotl(x,y) returns sqrtl(x^2+y^2) with error less
* than 1 ulps (units in the last place)
*/
#include <math.h>
#include <math_private.h>
#include <math-underflow.h>
#include <libm-alias-finite.h>
long double
__ieee754_hypotl(long double x, long double y)
{
long double a,b,a1,a2,b1,b2,w,kld;
int64_t j,k,ha,hb;
double xhi, yhi, hi, lo;
xhi = ldbl_high (x);
EXTRACT_WORDS64 (ha, xhi);
yhi = ldbl_high (y);
EXTRACT_WORDS64 (hb, yhi);
ha &= 0x7fffffffffffffffLL;
hb &= 0x7fffffffffffffffLL;
if(hb > ha) {a=y;b=x;j=ha; ha=hb;hb=j;} else {a=x;b=y;}
a = fabsl(a); /* a <- |a| */
b = fabsl(b); /* b <- |b| */
if((ha-hb)>0x0780000000000000LL) {return a+b;} /* x/y > 2**120 */
k=0;
kld = 1.0L;
if(ha > 0x5f30000000000000LL) { /* a>2**500 */
if(ha >= 0x7ff0000000000000LL) { /* Inf or NaN */
w = a+b; /* for sNaN */
if (issignaling (a) || issignaling (b))
return w;
if(ha == 0x7ff0000000000000LL)
w = a;
if(hb == 0x7ff0000000000000LL)
w = b;
return w;
}
/* scale a and b by 2**-600 */
a *= 0x1p-600L;
b *= 0x1p-600L;
k = 600;
kld = 0x1p+600L;
}
else if(hb < 0x23d0000000000000LL) { /* b < 2**-450 */
if(hb <= 0x000fffffffffffffLL) { /* subnormal b or 0 */
if(hb==0) return a;
a *= 0x1p+1022L;
b *= 0x1p+1022L;
k = -1022;
kld = 0x1p-1022L;
} else { /* scale a and b by 2^600 */
a *= 0x1p+600L;
b *= 0x1p+600L;
k = -600;
kld = 0x1p-600L;
}
}
/* medium size a and b */
w = a-b;
if (w>b) {
ldbl_unpack (a, &hi, &lo);
a1 = hi;
a2 = lo;
/* a*a + b*b
= (a1+a2)*a + b*b
= a1*a + a2*a + b*b
= a1*(a1+a2) + a2*a + b*b
= a1*a1 + a1*a2 + a2*a + b*b
= a1*a1 + a2*(a+a1) + b*b */
w = sqrtl(a1*a1-(b*(-b)-a2*(a+a1)));
} else {
a = a+a;
ldbl_unpack (b, &hi, &lo);
b1 = hi;
b2 = lo;
ldbl_unpack (a, &hi, &lo);
a1 = hi;
a2 = lo;
/* a*a + b*b
= a*a + (a-b)*(a-b) - (a-b)*(a-b) + b*b
= a*a + w*w - (a*a - 2*a*b + b*b) + b*b
= w*w + 2*a*b
= w*w + (a1+a2)*b
= w*w + a1*b + a2*b
= w*w + a1*(b1+b2) + a2*b
= w*w + a1*b1 + a1*b2 + a2*b */
w = sqrtl(a1*b1-(w*(-w)-(a1*b2+a2*b)));
}
if(k!=0)
{
w *= kld;
math_check_force_underflow_nonneg (w);
return w;
}
else
return w;
}
libm_alias_finite (__ieee754_hypotl, __hypotl)
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