Merge pull request cms-nanoAOD#64 from cms-nanoAOD/reduceMantissa2

Introduce limited precision for floats in post proc output

Author: arizzi

interface/ReduceMantissa.h

@@ -0,0 +1,31 @@
+#ifndef reducemantissa_h
+#define reducemantissa_h
+
+class ReduceMantissaToNbitsRounding {
+            public:
+                ReduceMantissaToNbitsRounding(int bits) : 
+                    shift(23-bits), mask((0xFFFFFFFF >> (shift)) << (shift)), 
+                    test(1 << (shift-1)), maxn((1<<bits)-2) {
+                        assert(bits <= 23); // "max mantissa size is 23 bits"
+                    }
+                float operator()(float f) const {
+                    constexpr uint32_t low23 = (0x007FFFFF); // mask to keep lowest 23 bits = mantissa
+                    constexpr uint32_t  hi9  = (0xFF800000); // mask to keep highest 9 bits = the rest
+                    union { float flt; uint32_t i32; } conv;
+                    conv.flt=f;
+                    if (conv.i32 & test) { // need to round
+                        uint32_t mantissa = (conv.i32 & low23) >> shift;
+                        if (mantissa < maxn) mantissa++;
+                        conv.i32 = (conv.i32 & hi9) | (mantissa << shift);
+                    } else {
+                        conv.i32 &= mask;
+                    }
+                    return conv.flt;
+                }
+            private:
+                const int shift;
+                const uint32_t mask, test, maxn;           
+};
+
+
+#endif

python/postprocessing/framework/output.py

@@ -7,11 +7,12 @@
 _rootBranchType2PythonArray = { 'b':'B', 'B':'b', 'i':'I', 'I':'i', 'F':'f', 'D':'d', 'l':'L', 'L':'l', 'O':'B' }
 
 class OutputBranch:
-    def __init__(self, tree, name, rootBranchType, n=1, lenVar=None, title=None):
+    def __init__(self, tree, name, rootBranchType, n=1, lenVar=None, title=None, limitedPrecision=False):
         n = int(n)
         self.buff   = array(_rootBranchType2PythonArray[rootBranchType], n*[0. if rootBranchType in 'FD' else 0])
         self.lenVar = lenVar
         self.n = n
+        self.precision = ROOT.ReduceMantissaToNbitsRounding(limitedPrecision) if limitedPrecision and rootBranchType=='F' else lambda x : x
         #check if a branch was already there 
         existingBranch = tree.GetBranch(name)
         if (existingBranch):
@@ -31,9 +32,9 @@ def fill(self, val):
             if len(self.buff) < len(val): # realloc
                 self.buff = array(self.buff.typecode, max(len(val),2*len(self.buff))*[0. if self.buff.typecode in 'fd' else 0])
                 self.branch.SetAddress(self.buff)
-            for i,v in enumerate(val): self.buff[i] = v
+            for i,v in enumerate(val): self.buff[i] = self.precision(v)
         elif self.n == 1: 
-            self.buff[0] = val
+            self.buff[0] = self.precision(val)
         else:
             if len(val) != self.n: raise RuntimeError("Mismatch in filling branch %s of fixed length %d with %d values (%s)" % (self.Branch.GetName(),self.n,len(val),val))
             for i,v in enumerate(val): self.buff[i] = v
@@ -44,10 +45,10 @@ def __init__(self, tfile, ttree, intree):
         self._tree = ttree
         self._intree = intree
         self._branches = {} 
-    def branch(self, name, rootBranchType, n=1, lenVar=None, title=None):
+    def branch(self, name, rootBranchType, n=1, lenVar=None, title=None,limitedPrecision=False):
         if (lenVar != None) and (lenVar not in self._branches): #and (not self._tree.GetBranch(lenVar)):
             self._branches[lenVar] = OutputBranch(self._tree, lenVar, "i")
-        self._branches[name] = OutputBranch(self._tree, name, rootBranchType, n=n, lenVar=lenVar, title=title)
+        self._branches[name] = OutputBranch(self._tree, name, rootBranchType, n=n, lenVar=lenVar, title=title,limitedPrecision=limitedPrecision)
         return self._branches[name]
     def fillBranch(self, name, val):
         br = self._branches[name]

src/classes.h

@@ -2,8 +2,10 @@
 #include "PhysicsTools/NanoAODTools/interface/PyJetResolutionScaleFactorWrapper.h"
 #include "PhysicsTools/NanoAODTools/interface/PyJetParametersWrapper.h"
 #include "PhysicsTools/NanoAODTools/interface/WeightCalculatorFromHistogram.h"
+#include "PhysicsTools/NanoAODTools/interface/ReduceMantissa.h"
 
 PyJetResolutionWrapper jetRes;
 PyJetResolutionScaleFactorWrapper jetResScaleFactor;
 PyJetParametersWrapper jetParams;
 WeightCalculatorFromHistogram wcalc;
+ReduceMantissaToNbitsRounding red(12);

src/classes_def.xml

@@ -4,5 +4,6 @@
   <class name="PyJetResolutionScaleFactorWrapper"/>
   <class name="PyJetParametersWrapper"/>
   <class name="WeightCalculatorFromHistogram"/>
+  <class name="ReduceMantissaToNbitsRounding"/>
 </selection>
 </lcgdict>