[PATCH v4 1/2] d2d1: Use 24-bit FP precision for triangulate.

[Brendan McGrath]

From: Brendan McGrath

This fixes a rendering issue (and ultimately a crash) in PowerPoint when
compiling with GCC 8.

GCC8 doesn't support the `excess-precision=standard` option under the
`#pragma GCC optimize` directive.

This results in unpredictable floating point rounding leading to errors
when inserting segments (with missing edges and/or triangles).

Using 24-bit precision ensures we don't have any excess precision.
---
 dlls/d2d1/geometry.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/dlls/d2d1/geometry.c b/dlls/d2d1/geometry.c
index d6ee91de005..9b0b7844739 100644
--- a/dlls/d2d1/geometry.c
+++ b/dlls/d2d1/geometry.c
@@ -16,10 +16,6 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
  */

-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC optimize "O2,no-strict-aliasing,excess-precision=standard"
-#endif
-
 #include "d2d1_private.h"
 #include <float.h>

@@ -1539,7 +1535,7 @@ static BOOL d2d_cdt_triangulate(struct d2d_cdt *cdt, size_t start_vertex, size_t
         return TRUE;
     }

-    /* More than tree vertices, divide. */
+    /* More than three vertices, divide. */
     cut = vertex_count / 2;
     if (!d2d_cdt_triangulate(cdt, start_vertex, cut, &left_outer, &left_inner))
         return FALSE;
@@ -2289,6 +2285,9 @@ static HRESULT d2d_path_geometry_triangulate(struct d2d_geometry *geometry)
     size_t vertex_count, i, j;
     struct d2d_cdt cdt = {0};
     D2D1_POINT_2F *vertices;
+#ifdef __i386__
+    unsigned int control_word_x87, mask = 0;
+#endif

for (i = 0, vertex_count = 0; i < geometry->u.path.figure_count; ++i)
     {
@@ -2339,10 +2338,20 @@ static HRESULT d2d_path_geometry_triangulate(struct d2d_geometry *geometry)

cdt.free_edge = ~0u;
     cdt.vertices = vertices;
+
+#ifdef __i386__
+    control_word_x87 = _controlfp(0, 0);
+    _controlfp(_PC_24, mask = _MCW_PC);
+#endif
     if (!d2d_cdt_triangulate(&cdt, 0, vertex_count, &left_edge, &right_edge))
         goto fail;
     if (!d2d_cdt_insert_segments(&cdt, geometry))
         goto fail;
+#ifdef __i386__
+    _controlfp(control_word_x87, _MCW_PC);
+    mask = 0;
+#endif
+
     if (!d2d_cdt_generate_faces(&cdt, geometry))
         goto fail;

@@ -2354,6 +2363,9 @@ fail:
     geometry->fill.vertex_count = 0;
     free(vertices);
     free(cdt.edges);
+#ifdef __i386__
+    if (mask) _controlfp(control_word_x87, mask);
+#endif
     return E_FAIL;
 }