[clang-tidy] Move incorrect-roundings to upstream.

Summary: This is originally implemented by Jacques Pienaar.

Reviewers: alexfh

Subscribers: cfe-commits, jpienaar

Differential Revision: http://reviews.llvm.org/D16764

llvm-svn: 260084

2 files changed, 13 insertions, 0 deletions

diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst b/clang-tools-extra/docs/clang-tidy/checks/list.rst
index aca429b0e43..42f7cf39022 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -49,6 +49,7 @@ Clang-Tidy Checks
    misc-bool-pointer-implicit-conversion
    misc-definitions-in-headers
    misc-inaccurate-erase
+   misc-incorrect-roundings
    misc-inefficient-algorithm
    misc-macro-parentheses
    misc-macro-repeated-side-effects
diff --git a/clang-tools-extra/docs/clang-tidy/checks/misc-incorrect-roundings.rst b/clang-tools-extra/docs/clang-tidy/checks/misc-incorrect-roundings.rst
new file mode 100644
index 00000000000..abe70b412b2
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/misc-incorrect-roundings.rst
@@ -0,0 +1,12 @@
+misc-incorrect-roundings
+========================
+
+Checks the usage of patterns known to produce incorrect rounding.
+Programmers often use
+  (int)(double_expression + 0.5)
+to round the double expression to an integer. The problem with this:
+
+1. It is unnecessarily slow.
+2. It is incorrect. The number 0.499999975 (smallest representable float
+   number below 0.5) rounds to 1.0. Even worse behavior for negative
+   numbers where both -0.5f and -1.4f both round to 0.0.