Mark Poliakov
7a0d528cda
git-subtree-dir: lib/runtime git-subtree-mainline: 566a2341f5b726d86f5d42a72beb9c70b83f31b6 git-subtree-split: db5cddbec10c4b7c086eda716d48d4711632901f
72 lines
1.4 KiB
C
72 lines
1.4 KiB
C
#include <stdint.h>
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#include "private.h"
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static const float one = 1.0, tiny=1.0e-30;
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float
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__ieee754_sqrtf(float x)
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{
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float z;
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int32_t sign = (int)0x80000000;
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int32_t ix,s,q,m,t,i;
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uint32_t r;
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GET_FLOAT_WORD(ix,x);
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/* take care of Inf and NaN */
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if((ix&0x7f800000)==0x7f800000) {
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return x*x+x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf
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sqrt(-inf)=sNaN */
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}
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/* take care of zero */
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if(ix<=0) {
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if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */
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else if(ix<0)
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return (x-x)/(x-x); /* sqrt(-ve) = sNaN */
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}
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/* normalize x */
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m = (ix>>23);
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if(m==0) { /* subnormal x */
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for(i=0;(ix&0x00800000)==0;i++) ix<<=1;
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m -= i-1;
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}
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m -= 127; /* unbias exponent */
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ix = (ix&0x007fffff)|0x00800000;
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if(m&1) /* odd m, double x to make it even */
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ix += ix;
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m >>= 1; /* m = [m/2] */
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/* generate sqrt(x) bit by bit */
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ix += ix;
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q = s = 0; /* q = sqrt(x) */
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r = 0x01000000; /* r = moving bit from right to left */
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while(r!=0) {
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t = s+r;
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if(t<=ix) {
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s = t+r;
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ix -= t;
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q += r;
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}
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ix += ix;
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r>>=1;
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}
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/* use floating add to find out rounding direction */
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if(ix!=0) {
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z = one-tiny; /* trigger inexact flag */
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if (z>=one) {
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z = one+tiny;
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if (z>one)
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q += 2;
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else
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q += (q&1);
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}
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}
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ix = (q>>1)+0x3f000000;
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ix += (m <<23);
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SET_FLOAT_WORD(z,ix);
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return z;
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}
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