glsl: Fix round64 conversion function

Fix round64 function to handle round to nearest even cases specially
with positive and negative numbers with fraction part 0.5.

v2: 1) Simplify unused bits (Elie Tournier)

Fixes:
   KHR-GL45.gpu_shader_fp64.builtin.round_dvec2
   KHR-GL45.gpu_shader_fp64.builtin.round_dvec3
   KHR-GL45.gpu_shader_fp64.builtin.round_dvec4
   KHR-GL45.gpu_shader_fp64.builtin.roundeven_double
   KHR-GL45.gpu_shader_fp64.builtin.roundeven_dvec2
   KHR-GL45.gpu_shader_fp64.builtin.roundeven_dvec3
   KHR-GL45.gpu_shader_fp64.builtin.roundeven_dvec4

Signed-off-by: Sagar Ghuge <[email protected]>
Reviewed-by: Elie Tournier <[email protected]>
Acked-by: Anuj Phogat <[email protected]>
(cherry picked from commit 06807e1948f1bced9806b00908c892f1e3c3db5b)

1 files changed, 12 insertions, 9 deletions

diff --git a/src/compiler/glsl/float64.glsl b/src/compiler/glsl/float64.glsl
index 415dde3907c..c92577c4e4c 100644
--- a/src/compiler/glsl/float64.glsl
+++ b/src/compiler/glsl/float64.glsl
@@ -1681,17 +1681,22 @@ __fround64(uint64_t __a)
 
    if (unbiasedExp < 20) {
       if (unbiasedExp < 0) {
+         if ((aHi & 0x80000000u) != 0u && aLo == 0u) {
+            return 0;
+         }
          aHi &= 0x80000000u;
-         if (unbiasedExp == -1 && aLo != 0u)
-            aHi |= (1023u << 20);
+         if ((a.y & 0x000FFFFFu) == 0u && a.x == 0u) {
+            aLo = 0u;
+            return packUint2x32(uvec2(aLo, aHi));
+         }
+         aHi = mix(aHi, (aHi | 0x3FF00000u), unbiasedExp == -1);
          aLo = 0u;
       } else {
          uint maskExp = 0x000FFFFFu >> unbiasedExp;
-         /* a is an integral value */
-         if (((aHi & maskExp) == 0u) && (aLo == 0u))
-            return __a;
-
+         uint lastBit = maskExp + 1;
          aHi += 0x00080000u >> unbiasedExp;
+         if ((aHi & maskExp) == 0u)
+            aHi &= ~lastBit;
          aHi &= ~maskExp;
          aLo = 0u;
       }
@@ -1708,9 +1713,7 @@ __fround64(uint64_t __a)
       aLo &= ~maskExp;
    }
 
-   a.x = aLo;
-   a.y = aHi;
-   return packUint2x32(a);
+   return packUint2x32(uvec2(aLo, aHi));
 }
 
 uint64_t