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gallivm: fix edge cases in exp2

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exp(0) has to be exactly 1, exp(-inf) has to be 0, exp(inf) has
to be inf and exp(nan) has to be nan, this fixes all of those
cases.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
This commit is contained in:
Zack Rusin 2013-07-18 02:38:54 -04:00
parent ab47bbecd6
commit 7b672c1503
1 changed files with 7 additions and 3 deletions
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10
src/gallium/auxiliary/gallivm/lp_bld_arit.c
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@ -3141,7 +3141,7 @@ lp_build_polynomial(struct lp_build_context *bld,
*/
const double lp_build_exp2_polynomial[] = {
#if EXP_POLY_DEGREE == 5
0.999999925063526176901,
1.000000000000000000000, /*XXX: was 0.999999925063526176901, recompute others */
0.693153073200168932794,
0.240153617044375388211,
0.0558263180532956664775,
@ -3196,8 +3196,12 @@ lp_build_exp2_approx(struct lp_build_context *bld,
assert(type.floating && type.width == 32);
x = lp_build_min(bld, x, lp_build_const_vec(bld->gallivm, type, 129.0));
x = lp_build_max(bld, x, lp_build_const_vec(bld->gallivm, type, -126.99999));
/* We want to preserve NaN and make sure than for exp2 if x > 128,
* the result is INF and if it's smaller than -126.9 the result is 0 */
x = lp_build_min_ext(bld, lp_build_const_vec(bld->gallivm, type, 128.0), x,
GALLIVM_NAN_RETURN_SECOND);
x = lp_build_max_ext(bld, lp_build_const_vec(bld->gallivm, type, -126.99999), x,
GALLIVM_NAN_RETURN_SECOND);
/* ipart = floor(x) */
/* fpart = x - ipart */