Fixed reference SIMD code to work with MSVC

Also noted minor issue with rounding to even. Using rint would be
preferable, but that's even harder to work around on MSVC.

Change-Id: I495cf2d43cf0b33cc0896958f15703ba8632c7e4

diff --git a/include/gmx_simd_ref.h b/include/gmx_simd_ref.h
index b20ab2f055309813a9b7cfa21865b7761c35689c..3454ccc7c6e6688882522f9a97ee195d34019942 100644 (file)
--- a/include/gmx_simd_ref.h
+++ b/include/gmx_simd_ref.h
@@ -236,9 +236,14 @@ gmx_simd_ref_blendzero_pr(gmx_simd_ref_pr a, gmx_simd_ref_pb b)
 }
 
 /* Note that this reference implementation rounds away from zero,
- * whereas most SIMD intrinsics will round to nearest even.
- * Since this function is only used for periodic image calculations,
- * the rounding of mantissas close to 0.5 is irrelevant.
+ * whereas most SIMD intrinsics will round to nearest even. Since this
+ * function is only used for periodic image calculations, the rounding
+ * of mantissas close to 0.5 is irrelevant, except in testing. This
+ * could be fixed by using rint/rintf, but the bigger problem is that
+ * MSVC does not support full C99, and none of the round or rint
+ * functions are defined. It's much easier to approximately implement
+ * round() than rint(), so we do that and hope we never get bitten in
+ * testing. (Thanks, Microsoft.)
  */
 static gmx_inline gmx_simd_ref_pr
 gmx_simd_ref_round_pr(gmx_simd_ref_pr a)
@@ -248,7 +253,12 @@ gmx_simd_ref_round_pr(gmx_simd_ref_pr a)
 
     for (i = 0; i < GMX_SIMD_REF_WIDTH; i++)
     {
-#ifdef GMX_DOUBLE
+#ifdef _MSC_VER
+        int temp = (a.r[i] >= 0.)
+            ? (a.r[i] + 0.5)
+            : (a.r[i] - 0.5);
+        b.r[i] = (real) temp;
+#elif defined GMX_DOUBLE
         b.r[i] = round(a.r[i]);
 #else
         b.r[i] = roundf(a.r[i]);