Add FxAlignToBoundary<>() template helper function.

Because I nearly botched this trivial calculation in the previous CL.

Change-Id: I7438f9d3476d93b7899c2d7d761234769f53f9e3
Reviewed-on: https://pdfium-review.googlesource.com/43010
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/core/fxcrt/fx_memory_unittest.cpp b/core/fxcrt/fx_memory_unittest.cpp
index 8c577835d6..eab11113cd 100644
--- a/core/fxcrt/fx_memory_unittest.cpp
+++ b/core/fxcrt/fx_memory_unittest.cpp
@@ -83,3 +83,26 @@ TEST(fxcrt, DISABLED_FXMEM_DefaultOOM) {
   EXPECT_FALSE(FXMEM_DefaultRealloc(ptr, kMaxByteAlloc));
   FXMEM_DefaultFree(ptr);
 }
+
+TEST(fxcrt, FXAlign) {
+  static_assert(std::numeric_limits<size_t>::max() % 2 == 1,
+                "numeric limit must be odd for this test");
+
+  size_t s0 = 0;
+  size_t s1 = 1;
+  size_t s2 = 2;
+  size_t sbig = std::numeric_limits<size_t>::max() - 2;
+  EXPECT_EQ(0u, FxAlignToBoundary<2>(s0));
+  EXPECT_EQ(2u, FxAlignToBoundary<2>(s1));
+  EXPECT_EQ(2u, FxAlignToBoundary<2>(s2));
+  EXPECT_EQ(std::numeric_limits<size_t>::max() - 1, FxAlignToBoundary<2>(sbig));
+
+  int i0 = 0;
+  int i511 = 511;
+  int i512 = 512;
+  int ineg = -513;
+  EXPECT_EQ(0, FxAlignToBoundary<512>(i0));
+  EXPECT_EQ(512, FxAlignToBoundary<512>(i511));
+  EXPECT_EQ(512, FxAlignToBoundary<512>(i512));
+  EXPECT_EQ(-512, FxAlignToBoundary<512>(ineg));
+}