[llvm-commits] (half precision) [llvm] r84239 - in /llvm/trunk: include/llvm/ADT/APFloat.h lib/Support/APFloat.cpp

[Chris Lattner]

On Oct 20, 2009, at 5:23 PM, Dale Johannesen wrote:

> Some testcases to exercise basic functionality would be nice.  I think
> there is a bug here that should have shown up in testing.

Peter, can you take a look at Dale's feedback?

-Chris

>
> On Oct 15, 2009, at 7:13 PM, Chris Lattner wrote:
>> +APInt
>> +APFloat::convertHalfAPFloatToAPInt() const
>> +{
>> +  assert(semantics == (const llvm::fltSemantics*)&IEEEhalf);
>> +  assert (partCount()==1);
>> +
>> +  uint32_t myexponent, mysignificand;
>> +
>> +  if (category==fcNormal) {
>> +    myexponent = exponent+15; //bias
>> +    mysignificand = (uint32_t)*significandParts();
>> +    if (myexponent == 1 && !(mysignificand & 0x400))
>> +      myexponent = 0;   // denormal
>> +  } else if (category==fcZero) {
>> +    myexponent = 0;
>> +    mysignificand = 0;
>> +  } else if (category==fcInfinity) {
>> +    myexponent = 0xff;
>
> 0x1f (doesn't matter functionally, but cleaner)
>
>> +    mysignificand = 0;
>> +  } else {
>> +    assert(category == fcNaN && "Unknown category!");
>> +    myexponent = 0xff;
>
> 0x1f
>
>> +    mysignificand = (uint32_t)*significandParts();
>> +  }
>> +
>> +  return APInt(16, (((sign&1) << 15) | ((myexponent&0x1f) << 10) |
>> +                    (mysignificand & 0x3ff)));
>> +}
>> +
>
>
>
>> +void
>> +APFloat::initFromHalfAPInt(const APInt & api)
>> +{
>> +  assert(api.getBitWidth()==16);
>> +  uint32_t i = (uint32_t)*api.getRawData();
>> +  uint32_t myexponent = (i >> 15) & 0x1f;
>
> Bug: should be >> 10
>
>> +  uint32_t mysignificand = i & 0x3ff;
>> +
>> +  initialize(&APFloat::IEEEhalf);
>> +  assert(partCount()==1);
>> +
>> +  sign = i >> 15;
>> +  if (myexponent==0 && mysignificand==0) {
>> +    // exponent, significand meaningless
>> +    category = fcZero;
>> +  } else if (myexponent==0x1f && mysignificand==0) {
>> +    // exponent, significand meaningless
>> +    category = fcInfinity;
>> +  } else if (myexponent==0x1f && mysignificand!=0) {
>> +    // sign, exponent, significand meaningless
>> +    category = fcNaN;
>> +    *significandParts() = mysignificand;
>> +  } else {
>> +    category = fcNormal;
>> +    exponent = myexponent - 15;  //bias
>> +    *significandParts() = mysignificand;
>> +    if (myexponent==0)    // denormal
>> +      exponent = -14;
>> +    else
>> +      *significandParts() |= 0x400; // integer bit
>> +  }
>> +}
>> +
>> /// Treat api as containing the bits of a floating point number.
>> Currently
>> /// we infer the floating point type from the size of the APInt.  The
>> /// isIEEE argument distinguishes between PPC128 and IEEE128 (not
>> meaningful
>> @@ -3058,7 +3124,9 @@
>
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