From c422b48bf43f9a1e2b29c4803c646de0617e32b4 Mon Sep 17 00:00:00 2001
From: "Christoph M. Wintersteiger" <cwinter@microsoft.com>
Date: Thu, 21 May 2015 15:06:47 +0100
Subject: [PATCH] Bugfix for hwf_manager::round_to_integral

---
 src/util/hwf.cpp | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/src/util/hwf.cpp b/src/util/hwf.cpp
index 40d20b644..b159cbdb6 100644
--- a/src/util/hwf.cpp
+++ b/src/util/hwf.cpp
@@ -338,8 +338,39 @@ void hwf_manager::sqrt(mpf_rounding_mode rm, hwf const & x, hwf & o) {
 
 void hwf_manager::round_to_integral(mpf_rounding_mode rm, hwf const & x, hwf & o) {
     set_rounding_mode(rm);
-    modf(x.value, &o.value);
-    // Note: on x64, this sometimes produces an SNAN instead of a QNAN?
+    // CMW: modf is not the right function here.
+    // modf(x.value, &o.value);
+
+    // According to the Intel Architecture manual, the x87-instrunction FRNDINT is the 
+    // same in 32-bit and 64-bit mode. The _mm_round_* intrinsics are SSE4 extensions.
+
+#ifdef USE_INTRINSICS
+    switch (rm) {
+    case 0: _mm_store_sd(&o.value, _mm_round_pd(_mm_set_sd(x.value), _MM_FROUND_TO_NEAREST_INT)); break;
+    case 2: _mm_store_sd(&o.value, _mm_round_pd(_mm_set_sd(x.value), _MM_FROUND_TO_POS_INF)); break;
+    case 3: _mm_store_sd(&o.value, _mm_round_pd(_mm_set_sd(x.value), _MM_FROUND_TO_NEG_INF)); break;
+    case 4: _mm_store_sd(&o.value, _mm_round_pd(_mm_set_sd(x.value), _MM_FROUND_TO_ZERO)); break;
+    case 1:
+        UNREACHABLE(); // Note: MPF_ROUND_NEAREST_TAWAY is not supported by the hardware!
+        break;
+    default:
+        UNREACHABLE(); // Unknown rounding mode.
+    }
+#else
+    NOT_IMPLEMENTED_YET();
+#endif
+
+#if 0
+    double xv = x.value;
+    double & ov = o.value;
+
+    __asm {
+        fld     xv
+        frndint
+        fstp    ov // Store result away.
+    }
+
+#endif
 }
 
 void hwf_manager::rem(hwf const & x, hwf const & y, hwf & o) {