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Adjust the exponent before converting the result from double to

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float precision. This fixes some double rounding problems for
subnormals and simplifies things a bit.
This commit is contained in:
David Schultz 2008-01-28 01:19:07 +00:00
parent 86ca3fd005
commit b134ea7211
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=175731
1 changed files with 10 additions and 16 deletions
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26
lib/msun/src/s_exp2f.c
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@ -93,12 +93,12 @@ float
exp2f(float x)
{
double tv;
float r, t, z;
uint32_t hx, hr, ix, i0;
float t, z;
uint32_t hx, htv, ix, i0;
int32_t k;
/* Filter out exceptional cases. */
GET_FLOAT_WORD(hx,x);
GET_FLOAT_WORD(hx, x);
ix = hx & 0x7fffffff; /* high word of |x| */
if(ix >= 0x43000000) { /* |x| >= 128 */
if(ix >= 0x7f800000) {
@ -119,25 +119,19 @@ exp2f(float x)
STRICT_ASSIGN(float, t, x + redux);
GET_FLOAT_WORD(i0, t);
i0 += TBLSIZE / 2;
k = (i0 >> TBLBITS) << 23;
k = (i0 >> TBLBITS) << 20;
i0 &= TBLSIZE - 1;
t -= redux;
z = x - t;
/* Compute r = exp2(y) = exp2ft[i0] * p(z). */
tv = exp2ft[i0];
r = tv + tv * (z * (P1 + z * (P2 + z * (P3 + z * P4))));
tv = tv + tv * (z * (P1 + z * (P2 + z * (P3 + z * P4))));
/* Scale by 2**(k>>23). */
if(k >= -125 << 23) {
if (k != 0) {
GET_FLOAT_WORD(hr, r);
SET_FLOAT_WORD(r, hr + k);
}
return (r);
} else {
GET_FLOAT_WORD(hr, r);
SET_FLOAT_WORD(r, hr + (k + (100 << 23)));
return (r * twom100);
/* Scale by 2**(k>>20). */
if (k != 0) {
GET_HIGH_WORD(htv, tv);
SET_HIGH_WORD(tv, htv + k);
}
return (tv);
}