C++: use rounding to prevent float wobble in range analysis

Author: rdmarsh2

cpp/ql/lib/experimental/semmle/code/cpp/semantic/analysis/FloatDelta.qll

@@ -16,6 +16,5 @@ module FloatDelta implements DeltaSig {
   Delta fromInt(int n) { result = n }
 
   bindingset[f]
-  bindingset[result]
-  Delta fromFloat(float f) { result = f }
+  Delta fromFloat(float f) { result = min(float diff, float res | diff = (res - f).abs() and res = f.ceil() or diff = (f - res).abs() and res = f.floor() | res order by diff )}
 }

cpp/ql/lib/experimental/semmle/code/cpp/semantic/analysis/RangeAnalysisSpecific.qll

@@ -5,6 +5,7 @@
 private import experimental.semmle.code.cpp.semantic.Semantic
 private import RangeAnalysisStage
 private import experimental.semmle.code.cpp.semantic.analysis.FloatDelta
+private import experimental.semmle.code.cpp.semantic.analysis.IntDelta
 
 module CppLangImpl implements LangSig<FloatDelta> {
   /**