84 lines
1.8 KiB
C
84 lines
1.8 KiB
C
/* origin: FreeBSD /usr/src/lib/msun/src/e_sqrtf.c */
|
|
/*
|
|
* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
|
|
*/
|
|
/*
|
|
* ====================================================
|
|
* 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.
|
|
* ====================================================
|
|
*/
|
|
|
|
#include "libc/math/libm.h"
|
|
|
|
static const float tiny = 1.0e-30;
|
|
|
|
float sqrtf(float x)
|
|
{
|
|
float z;
|
|
int32_t sign = (int)0x80000000;
|
|
int32_t ix,s,q,m,t,i;
|
|
uint32_t r;
|
|
|
|
GET_FLOAT_WORD(ix, x);
|
|
|
|
/* take care of Inf and NaN */
|
|
if ((ix&0x7f800000) == 0x7f800000)
|
|
return x*x + x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf, sqrt(-inf)=sNaN */
|
|
|
|
/* take care of zero */
|
|
if (ix <= 0) {
|
|
if ((ix&~sign) == 0)
|
|
return x; /* sqrt(+-0) = +-0 */
|
|
if (ix < 0)
|
|
return (x-x)/(x-x); /* sqrt(-ve) = sNaN */
|
|
}
|
|
/* normalize x */
|
|
m = ix>>23;
|
|
if (m == 0) { /* subnormal x */
|
|
for (i = 0; (ix&0x00800000) == 0; i++)
|
|
ix<<=1;
|
|
m -= i - 1;
|
|
}
|
|
m -= 127; /* unbias exponent */
|
|
ix = (ix&0x007fffff)|0x00800000;
|
|
if (m&1) /* odd m, double x to make it even */
|
|
ix += ix;
|
|
m >>= 1; /* m = [m/2] */
|
|
|
|
/* generate sqrt(x) bit by bit */
|
|
ix += ix;
|
|
q = s = 0; /* q = sqrt(x) */
|
|
r = 0x01000000; /* r = moving bit from right to left */
|
|
|
|
while (r != 0) {
|
|
t = s + r;
|
|
if (t <= ix) {
|
|
s = t+r;
|
|
ix -= t;
|
|
q += r;
|
|
}
|
|
ix += ix;
|
|
r >>= 1;
|
|
}
|
|
|
|
/* use floating add to find out rounding direction */
|
|
if (ix != 0) {
|
|
z = 1.0f - tiny; /* raise inexact flag */
|
|
if (z >= 1.0f) {
|
|
z = 1.0f + tiny;
|
|
if (z > 1.0f)
|
|
q += 2;
|
|
else
|
|
q += q & 1;
|
|
}
|
|
}
|
|
ix = (q>>1) + 0x3f000000;
|
|
SET_FLOAT_WORD(z, ix + ((uint32_t)m << 23));
|
|
return z;
|
|
}
|