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puzzles: faster, smaller sqrt()

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Change-Id: I18e170ee49bff131fe76fa4bb1b9e0f120818b82
This commit is contained in:
Franklin Wei 2017-08-17 17:14:21 -04:00
parent f2f1889b10
commit ec1a74a37c
1 changed files with 7 additions and 61 deletions
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68
apps/plugins/puzzles/rbwrappers.c
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@ -984,70 +984,16 @@ float atan2_wrapper(float y, float x)
} }
} }
/* Square root function, original. */
float sqrt_wrapper(float x) float sqrt_wrapper(float x)
{ {
float z; /* find inverse, Quake-style */
int32_t sign = (int)0x80000000; float xhalf = .5f * x;
int32_t ix,s,q,m,t,i; int i = *(int*)&x;
uint32_t r; i = 0x5f3759df - (i >> 1);
x = *(float*)&i;
x = x * (1.5f - (xhalf * x * x));
GET_FLOAT_WORD(ix,x); return 1.0f / 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 */
else 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 = one-tiny; /* trigger inexact flag */
if (z>=one) {
z = one+tiny;
if (z>one)
q += 2;
else
q += (q&1);
}
}
ix = (q>>1)+0x3f000000;
ix += (m <<23);
SET_FLOAT_WORD(z,ix);
return z;
} }
/* hack, simple trig */ /* hack, simple trig */