Add getSizeInBits function to the APFloat class

[tberghammer]

Summary

Add getSizeInBits function to the APFloat class

The newly added function returns the size of the specified floating point semantics in bits.

[tberghammer]

The function will be first used from LLDB

[bkramer]

This is wrong for x87 long doubles (implicit '1' always present, so the count is off by one) and PPC double doubles (weird 128 bit format). It's probably best to just hardcode the value for all supported fp formats.

[tberghammer]

Use hard coded size values

[hfinkel]

lib/Support/APFloat.cpp

3374

Why not just add this number to the fltSemantics structure itself?

[tberghammer]

lib/Support/APFloat.cpp

3374

I think it is not really part of the semantic, but I can move it to there if you want.
If I move it into the semantic then what should be the size value of calcSemantic in roundSignificandWithExponent? It isn't used by anybody (yet) but we still should give it a reasonable value.

[tberghammer]

Friendly ping

[chandlerc]

I think I agree with Hal and this should be in the semantic struct. Open to other suggestions though.

[tberghammer]

Move size into the semantics

[tberghammer]

Friendly ping

[tberghammer]

Friendly ping

[tberghammer]

Friendly ping

[hfinkel]

LGTM.

lib/Support/APFloat.cpp

3372

This { should be on the previous line.

3374

If I move it into the semantic then what should be the size value of calcSemantic in roundSignificandWithExponent? It isn't used by anybody (yet) but we still should give it a reasonable value.

I'd just leave it as 0 as you now have it. It also has 0 precision ;)

include/llvm/ADT/APFloat.h

static APFloat getSmallestNormalized(const fltSemantics &Sem,
                                        bool Negative = false);
 
   /// Returns a float which is bitcasted from an all one value int.
   ///
   /// \param BitWidth - Select float type
   /// \param isIEEE   - If 128 bit number, select between PPC and IEEE
   static APFloat getAllOnesValue(unsigned BitWidth, bool isIEEE = false);
 
+  /// Returns the size of the floating point number (in bits) in the given
+  /// semantics.
+  static unsigned getSizeInBits(const fltSemantics &Sem);
+
   /// @}
 
   /// Used to insert APFloat objects, or objects that contain APFloat objects,
   /// into FoldingSets.
   void Profile(FoldingSetNodeID &NID) const;
 
   /// \brief Used by the Bitcode serializer to emit APInts to Bitcode.
   void Emit(Serializer &S) const;

lib/Support/APFloat.cpp

case 128:
     if (isIEEE)
       return APFloat(IEEEquad, APInt::getAllOnesValue(BitWidth));
     return APFloat(PPCDoubleDouble, APInt::getAllOnesValue(BitWidth));
   default:
     llvm_unreachable("Unknown floating bit width");
   }
 }
 
+unsigned APFloat::getSizeInBits(const fltSemantics &Sem)
+{
+  // sign bit + mantissa
+  unsigned size = 1 + Sem.precision;
+
+  // Add size of the exponent
+  ExponentType ex = Sem.maxExponent;
+  while (ex) {
+    ex >>= 1;
+    size++;
+  }
+
+  return size;
+}
+
 /// Make this number the largest magnitude normal number in the given
 /// semantics.
 void APFloat::makeLargest(bool Negative) {
   // We want (in interchange format):
   //   sign = {Negative}
   //   exponent = 1..10
   //   significand = 1..1
   category = fcNormal;