mesa,glsl: Move round_to_even() from glsl to mesa/main (v2)

Move round_to_even's definition to mesa/main so that _mesa_float_to_half()
can use it in order to eliminate rounding bias.

In additon to moving the fuction definition, prefix its name with "_mesa",
just as all other functions in mesa/main are prefixed.

v2: Fix Android build.

Reviewed-by: Ian Romanick <[email protected]>
Signed-off-by: Chad Versace <[email protected]>

2 files changed, 23 insertions, 0 deletions

diff --git a/src/mesa/main/imports.c b/src/mesa/main/imports.c
index 76f835e0ec3..26c91dce535 100644
--- a/src/mesa/main/imports.c
+++ b/src/mesa/main/imports.c
@@ -314,6 +314,26 @@ _mesa_bitcount_64(uint64_t n)
 #endif
 
 
+/* Using C99 rounding functions for roundToEven() implementation is
+ * difficult, because round(), rint, and nearbyint() are affected by
+ * fesetenv(), which the application may have done for its own
+ * purposes.  Mesa's IROUND macro is close to what we want, but it
+ * rounds away from 0 on n + 0.5.
+ */
+int
+_mesa_round_to_even(float val)
+{
+   int rounded = IROUND(val);
+
+   if (val - floor(val) == 0.5) {
+      if (rounded % 2 != 0)
+         rounded += val > 0 ? -1 : 1;
+   }
+
+   return rounded;
+}
+
+
 /**
  * Convert a 4-byte float to a 2-byte half float.
  * Based on code from:
diff --git a/src/mesa/main/imports.h b/src/mesa/main/imports.h
index 8446ea2a3e8..4b783818b2f 100644
--- a/src/mesa/main/imports.h
+++ b/src/mesa/main/imports.h
@@ -548,6 +548,9 @@ _mesa_fls(unsigned int n)
 #endif
 }
 
+extern int
+_mesa_round_to_even(float val);
+
 extern GLhalfARB
 _mesa_float_to_half(float f);