gallivm: Add a note about SSE4.1's nearest mode rounding.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_arit.c b/src/gallium/auxiliary/gallivm/lp_bld_arit.c
index 00f419a486d..f9a12a41a1b 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_arit.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_arit.c
@@ -983,6 +983,12 @@ enum lp_build_round_sse41_mode
 };
 
 
+/**
+ * Helper for SSE4.1's ROUNDxx instructions.
+ *
+ * NOTE: In the SSE4.1's nearest mode, if two values are equally close, the
+ * result is the even value.  That is, rounding 2.5 will be 2.0, and not 3.0.
+ */
 static INLINE LLVMValueRef
 lp_build_round_sse41(struct lp_build_context *bld,
                      LLVMValueRef a,