* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
* Debugged and optimized by Bruce D. Evans.
*/
* ====================================================
* 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.
* ====================================================
*/
* Return cube root of x
*/
#include <math.h>
#include <stdint.h>
static const unsigned
B1 = 709958130,
B2 = 642849266;
float cbrtf(float x)
{
double_t r,T;
union {float f; uint32_t i;} u = {x};
uint32_t hx = u.i & 0x7fffffff;
if (hx >= 0x7f800000)
return x + x;
if (hx < 0x00800000) {
if (hx == 0)
return x;
u.f = x*0x1p24f;
hx = u.i & 0x7fffffff;
hx = hx/3 + B2;
} else
hx = hx/3 + B1;
u.i &= 0x80000000;
u.i |= hx;
* First step Newton iteration (solving t*t-x/t == 0) to 16 bits. In
* double precision so that its terms can be arranged for efficiency
* without causing overflow or underflow.
*/
T = u.f;
r = T*T*T;
T = T*((double_t)x+x+r)/(x+r+r);
* Second step Newton iteration to 47 bits. In double precision for
* efficiency and accuracy.
*/
r = T*T*T;
T = T*((double_t)x+x+r)/(x+r+r);
return T;
}
