...
author Shinji KONO Mon, 25 May 2020 18:13:55 +0900 1830386684a0
line wrap: on
line source
```
/* e_hypotl.c -- long double version of e_hypot.c.
* Conversion to long double by Jakub Jelinek, jakub@redhat.com.
*/

/*
* ====================================================
*
* 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.
* ====================================================
*/

/* hypotq(x,y)
*
* Method :
*	If (assume round-to-nearest) z=x*x+y*y
*	has error less than sqrtq(2)/2 ulp, than
*	sqrtq(z) has error less than 1 ulp (exercise).
*
*	So, compute sqrtq(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 64 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 64 bits cleared, t2 = 2x-t1,
*	y1= y with lower 64 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 sqrtq(x^2+y^2) with error less
*	than 1 ulps (units in the last place)
*/

__float128
hypotq(__float128 x, __float128 y)
{
__float128 a,b,t1,t2,y1,y2,w;
int64_t j,k,ha,hb;

GET_FLT128_MSW64(ha,x);
ha &= 0x7fffffffffffffffLL;
GET_FLT128_MSW64(hb,y);
hb &= 0x7fffffffffffffffLL;
if(hb > ha) {a=y;b=x;j=ha; ha=hb;hb=j;} else {a=x;b=y;}
SET_FLT128_MSW64(a,ha);	/* a <- |a| */
SET_FLT128_MSW64(b,hb);	/* b <- |b| */
if((ha-hb)>0x78000000000000LL) {return a+b;} /* x/y > 2**120 */
k=0;
if(ha > 0x5f3f000000000000LL) {	/* a>2**8000 */
if(ha >= 0x7fff000000000000LL) {	/* Inf or NaN */
uint64_t low;
w = a+b;			/* for sNaN */
if (issignalingq (a) || issignalingq (b))
return w;
GET_FLT128_LSW64(low,a);
if(((ha&0xffffffffffffLL)|low)==0) w = a;
GET_FLT128_LSW64(low,b);
if(((hb^0x7fff000000000000LL)|low)==0) w = b;
return w;
}
/* scale a and b by 2**-9600 */
ha -= 0x2580000000000000LL;
hb -= 0x2580000000000000LL;	k += 9600;
SET_FLT128_MSW64(a,ha);
SET_FLT128_MSW64(b,hb);
}
if(hb < 0x20bf000000000000LL) {	/* b < 2**-8000 */
if(hb <= 0x0000ffffffffffffLL) {	/* subnormal b or 0 */
uint64_t low;
GET_FLT128_LSW64(low,b);
if((hb|low)==0) return a;
t1=0;
SET_FLT128_MSW64(t1,0x7ffd000000000000LL); /* t1=2^16382 */
b *= t1;
a *= t1;
k -= 16382;
GET_FLT128_MSW64 (ha, a);
GET_FLT128_MSW64 (hb, b);
if (hb > ha)
{
t1 = a;
a = b;
b = t1;
j = ha;
ha = hb;
hb = j;
}
} else {		/* scale a and b by 2^9600 */
ha += 0x2580000000000000LL;	/* a *= 2^9600 */
hb += 0x2580000000000000LL;	/* b *= 2^9600 */
k -= 9600;
SET_FLT128_MSW64(a,ha);
SET_FLT128_MSW64(b,hb);
}
}
/* medium size a and b */
w = a-b;
if (w>b) {
t1 = 0;
SET_FLT128_MSW64(t1,ha);
t2 = a-t1;
w  = sqrtq(t1*t1-(b*(-b)-t2*(a+t1)));
} else {
a  = a+a;
y1 = 0;
SET_FLT128_MSW64(y1,hb);
y2 = b - y1;
t1 = 0;
SET_FLT128_MSW64(t1,ha+0x0001000000000000LL);
t2 = a - t1;
w  = sqrtq(t1*y1-(w*(-w)-(t1*y2+t2*b)));
}
if(k!=0) {
uint64_t high;
t1 = 1;
GET_FLT128_MSW64(high,t1);
SET_FLT128_MSW64(t1,high+(k<<48));
w *= t1;
math_check_force_underflow_nonneg (w);
return w;
} else return w;
}
```