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runtime: add kernel-accessible sqrt.

Fixes #382.
This commit is contained in:
whitequark 2016-04-06 23:17:42 +00:00 committed by Sebastien Bourdeauducq
parent 2248a2eb9e
commit 904379db7e
1 changed files with 103 additions and 0 deletions

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@ -18,6 +18,7 @@
#include "i2c.h"
double round(double x);
double sqrt(double x);
void ksupport_abort(void);
static void attribute_writeback(void *);
@ -87,6 +88,7 @@ static const struct symbol runtime_exports[] = {
/* libm */
{"round", &round},
{"sqrt", &sqrt},
/* exceptions */
{"_Unwind_Resume", &_Unwind_Resume},
@ -161,6 +163,107 @@ double round(double x)
return y;
}
double sqrt(double x)
{
static const double one = 1.0, tiny = 1.0e-300;
double z;
int32_t sign = (int)0x80000000;
int32_t ix0,s0,q,m,t,i;
uint32_t r,t1,s1,ix1,q1;
union {double f; struct{uint32_t msw; uint32_t lsw;};} u = {x};
ix0 = u.msw;
ix1 = u.lsw;
/* take care of Inf and NaN */
if((ix0&0x7ff00000)==0x7ff00000) {
return x*x+x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf
sqrt(-inf)=sNaN */
}
/* take care of zero */
if(ix0<=0) {
if(((ix0&(~sign))|ix1)==0) return x;/* sqrt(+-0) = +-0 */
else if(ix0<0)
return (x-x)/(x-x); /* sqrt(-ve) = sNaN */
}
/* normalize x */
m = (ix0>>20);
if(m==0) { /* subnormal x */
while(ix0==0) {
m -= 21;
ix0 |= (ix1>>11); ix1 <<= 21;
}
for(i=0;(ix0&0x00100000)==0;i++) ix0<<=1;
m -= i-1;
ix0 |= (ix1>>(32-i));
ix1 <<= i;
}
m -= 1023; /* unbias exponent */
ix0 = (ix0&0x000fffff)|0x00100000;
if(m&1){ /* odd m, double x to make it even */
ix0 += ix0 + ((ix1&sign)>>31);
ix1 += ix1;
}
m >>= 1; /* m = [m/2] */
/* generate sqrt(x) bit by bit */
ix0 += ix0 + ((ix1&sign)>>31);
ix1 += ix1;
q = q1 = s0 = s1 = 0; /* [q,q1] = sqrt(x) */
r = 0x00200000; /* r = moving bit from right to left */
while(r!=0) {
t = s0+r;
if(t<=ix0) {
s0 = t+r;
ix0 -= t;
q += r;
}
ix0 += ix0 + ((ix1&sign)>>31);
ix1 += ix1;
r>>=1;
}
r = sign;
while(r!=0) {
t1 = s1+r;
t = s0;
if((t<ix0)||((t==ix0)&&(t1<=ix1))) {
s1 = t1+r;
if(((t1&sign)==sign)&&(s1&sign)==0) s0 += 1;
ix0 -= t;
if (ix1 < t1) ix0 -= 1;
ix1 -= t1;
q1 += r;
}
ix0 += ix0 + ((ix1&sign)>>31);
ix1 += ix1;
r>>=1;
}
/* use floating add to find out rounding direction */
if((ix0|ix1)!=0) {
z = one-tiny; /* trigger inexact flag */
if (z>=one) {
z = one+tiny;
if (q1==(uint32_t)0xffffffff) { q1=0; q += 1;}
else if (z>one) {
if (q1==(uint32_t)0xfffffffe) q+=1;
q1+=2;
} else
q1 += (q1&1);
}
}
ix0 = (q>>1)+0x3fe00000;
ix1 = q1>>1;
if ((q&1)==1) ix1 |= sign;
ix0 += (m <<20);
u.msw = ix0;
u.lsw = ix1;
return u.f;
}
/* called by libunwind */
int fprintf(FILE *stream, const char *fmt, ...)
{