gallivm: Updated lp_build_log2_approx to use a more accurate polynomial.

Tested with lp_test_arit with 100% passes and piglit tests with 100%
pass for log but some tests still fail for pow.

Signed-off-by: José Fonseca <[email protected]>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/gallium/auxiliary/gallivm/f.cpp b/src/gallium/auxiliary/gallivm/f.cpp
index 7cb50f16c0f..4b33e49b477 100644
--- a/src/gallium/auxiliary/gallivm/f.cpp
+++ b/src/gallium/auxiliary/gallivm/f.cpp
@@ -41,11 +41,11 @@
  *
  *  and take the coefficients from the P = { ... } array.
  *
- * - To compute log2 5th order polynomial between [1, 2] do:
+ * - To compute log2 4th order polynomial between [0, 1/9] do:
  *
  *    variant 1
- *    range 1 2
- *    order 5 0
+ *    range 0 0.111111112
+ *    order 4 0
  *    step 200
  *    info
  *
@@ -77,7 +77,7 @@ boost::math::ntl::RR f(const boost::math::ntl::RR& x, int variant)
       return exp2(x);
 
    case 1:
-      return log2(x)/(x - 1.0);
+      return log2((1.0 + sqrt(x))/(1.0 - sqrt(x)))/sqrt(x);
    }
 
    return 0;