SDL  2.0
Functions | Variables
k_rem_pio2.c File Reference
#include "math_libm.h"
#include "math_private.h"
#include "SDL_assert.h"
+ Include dependency graph for k_rem_pio2.c:

Go to the source code of this file.

Functions

int32_t attribute_hidden __kernel_rem_pio2 (double *x, double *y, int e0, int nx, const unsigned int prec, const int32_t *ipio2)

Variables

static const int init_jk [] = {2,3,4,6}
static const double PIo2 []
static const double zero = 0.0
static const double one = 1.0
static const double two24 = 1.67772160000000000000e+07
static const double twon24 = 5.96046447753906250000e-08

Function Documentation

int32_t attribute_hidden __kernel_rem_pio2 ( double *  x,
double *  y,
int  e0,
int  nx,
const unsigned int  prec,
const int32_t *  ipio2 
)

Definition at line 152 of file k_rem_pio2.c.

References floor(), i, init_jk, j, k, one, PIo2, scalbn, SDL_arraysize, SDL_assert, SDL_memset, two24, twon24, and zero.

Referenced by __ieee754_rem_pio2().

{
int32_t jz,jx,jv,jp,jk,carry,n,iq[20],i,j,k,m,q0,ih;
double z,fw,f[20],fq[20],q[20];
if (nx < 1) {
return 0;
}
/* initialize jk*/
SDL_assert(prec < SDL_arraysize(init_jk));
jk = init_jk[prec];
SDL_assert(jk > 0);
jp = jk;
/* determine jx,jv,q0, note that 3>q0 */
jx = nx-1;
jv = (e0-3)/24; if(jv<0) jv=0;
q0 = e0-24*(jv+1);
/* set up f[0] to f[jx+jk] where f[jx+jk] = ipio2[jv+jk] */
j = jv-jx; m = jx+jk;
for(i=0;i<=m;i++,j++) f[i] = (j<0)? zero : (double) ipio2[j];
if ((m+1) < SDL_arraysize(f)) {
SDL_memset(&f[m+1], 0, sizeof (f) - ((m+1) * sizeof (f[0])));
}
/* compute q[0],q[1],...q[jk] */
for (i=0;i<=jk;i++) {
for(j=0,fw=0.0;j<=jx;j++) fw += x[j]*f[jx+i-j];
q[i] = fw;
}
jz = jk;
recompute:
/* distill q[] into iq[] reversingly */
for(i=0,j=jz,z=q[jz];j>0;i++,j--) {
fw = (double)((int32_t)(twon24* z));
iq[i] = (int32_t)(z-two24*fw);
z = q[j-1]+fw;
}
if (jz < SDL_arraysize(iq)) {
SDL_memset(&iq[jz], 0, sizeof (q) - (jz * sizeof (iq[0])));
}
/* compute n */
z = scalbn(z,q0); /* actual value of z */
z -= 8.0*floor(z*0.125); /* trim off integer >= 8 */
n = (int32_t) z;
z -= (double)n;
ih = 0;
if(q0>0) { /* need iq[jz-1] to determine n */
i = (iq[jz-1]>>(24-q0)); n += i;
iq[jz-1] -= i<<(24-q0);
ih = iq[jz-1]>>(23-q0);
}
else if(q0==0) ih = iq[jz-1]>>23;
else if(z>=0.5) ih=2;
if(ih>0) { /* q > 0.5 */
n += 1; carry = 0;
for(i=0;i<jz ;i++) { /* compute 1-q */
j = iq[i];
if(carry==0) {
if(j!=0) {
carry = 1; iq[i] = 0x1000000- j;
}
} else iq[i] = 0xffffff - j;
}
if(q0>0) { /* rare case: chance is 1 in 12 */
switch(q0) {
case 1:
iq[jz-1] &= 0x7fffff; break;
case 2:
iq[jz-1] &= 0x3fffff; break;
}
}
if(ih==2) {
z = one - z;
if(carry!=0) z -= scalbn(one,q0);
}
}
/* check if recomputation is needed */
if(z==zero) {
j = 0;
for (i=jz-1;i>=jk;i--) j |= iq[i];
if(j==0) { /* need recomputation */
for(k=1;iq[jk-k]==0;k++); /* k = no. of terms needed */
for(i=jz+1;i<=jz+k;i++) { /* add q[jz+1] to q[jz+k] */
f[jx+i] = (double) ipio2[jv+i];
for(j=0,fw=0.0;j<=jx;j++) fw += x[j]*f[jx+i-j];
q[i] = fw;
}
jz += k;
goto recompute;
}
}
/* chop off zero terms */
if(z==0.0) {
jz -= 1; q0 -= 24;
SDL_assert(jz >= 0);
while(iq[jz]==0) { jz--; SDL_assert(jz >= 0); q0-=24;}
} else { /* break z into 24-bit if necessary */
z = scalbn(z,-q0);
if(z>=two24) {
fw = (double)((int32_t)(twon24*z));
iq[jz] = (int32_t)(z-two24*fw);
jz += 1; q0 += 24;
iq[jz] = (int32_t) fw;
} else iq[jz] = (int32_t) z ;
}
/* convert integer "bit" chunk to floating-point value */
fw = scalbn(one,q0);
for(i=jz;i>=0;i--) {
q[i] = fw*(double)iq[i]; fw*=twon24;
}
/* compute PIo2[0,...,jp]*q[jz,...,0] */
for(i=jz;i>=0;i--) {
for(fw=0.0,k=0;k<=jp&&k<=jz-i;k++) fw += PIo2[k]*q[i+k];
fq[jz-i] = fw;
}
if ((jz+1) < SDL_arraysize(f)) {
SDL_memset(&fq[jz+1], 0, sizeof (fq) - ((jz+1) * sizeof (fq[0])));
}
/* compress fq[] into y[] */
switch(prec) {
case 0:
fw = 0.0;
for (i=jz;i>=0;i--) fw += fq[i];
y[0] = (ih==0)? fw: -fw;
break;
case 1:
case 2:
fw = 0.0;
for (i=jz;i>=0;i--) fw += fq[i];
y[0] = (ih==0)? fw: -fw;
fw = fq[0]-fw;
for (i=1;i<=jz;i++) fw += fq[i];
y[1] = (ih==0)? fw: -fw;
break;
case 3: /* painful */
for (i=jz;i>0;i--) {
fw = fq[i-1]+fq[i];
fq[i] += fq[i-1]-fw;
fq[i-1] = fw;
}
for (i=jz;i>1;i--) {
fw = fq[i-1]+fq[i];
fq[i] += fq[i-1]-fw;
fq[i-1] = fw;
}
for (fw=0.0,i=jz;i>=2;i--) fw += fq[i];
if(ih==0) {
y[0] = fq[0]; y[1] = fq[1]; y[2] = fw;
} else {
y[0] = -fq[0]; y[1] = -fq[1]; y[2] = -fw;
}
}
return n&7;
}

Variable Documentation

const int init_jk[] = {2,3,4,6}
static

Definition at line 133 of file k_rem_pio2.c.

Referenced by __kernel_rem_pio2().

const double one = 1.0
static

Definition at line 148 of file k_rem_pio2.c.

Referenced by __kernel_rem_pio2().

const double PIo2[]
static
Initial value:
{
1.57079625129699707031e+00,
7.54978941586159635335e-08,
5.39030252995776476554e-15,
3.28200341580791294123e-22,
1.27065575308067607349e-29,
1.22933308981111328932e-36,
2.73370053816464559624e-44,
2.16741683877804819444e-51,
}

Definition at line 135 of file k_rem_pio2.c.

Referenced by __kernel_rem_pio2().

const double two24 = 1.67772160000000000000e+07
static

Definition at line 149 of file k_rem_pio2.c.

Referenced by __kernel_rem_pio2().

const double twon24 = 5.96046447753906250000e-08
static

Definition at line 150 of file k_rem_pio2.c.

Referenced by __kernel_rem_pio2().

const double zero = 0.0
static

Definition at line 147 of file k_rem_pio2.c.

Referenced by __kernel_rem_pio2().