[llvm-commits] [llvm] r113996 - in /llvm/trunk: include/llvm/MC/MCInst.h lib/Target/ARM/ARMMCInstLower.cpp lib/Target/ARM/AsmPrinter/ARMInstPrinter.cpp

[Stephen Canon]

On Sep 15, 2010, at 2:41 PM, Jim Grosbach wrote:

> On Sep 15, 2010, at 1:52 PM, Stephen Canon wrote:
> 
>> On Sep 15, 2010, at 1:05 PM, Dale Johannesen wrote:
>> 
>>> On Sep 15, 2010, at 11:47 AMPDT, Jim Grosbach wrote:
>>> 
>>>> Author: grosbach
>>>> Date: Wed Sep 15 13:47:08 2010
>>>> New Revision: 113996
>>>> 
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=113996&view=rev
>>>> Log:
>>>> Add support for floating point immediates to MC instruction printing. ARM
>>>> VFP instructions use it for loading some constants, so implement that
>>>> handling.
>>>> 
>>>> Not thrilled with adding a member to MCOperand, but not sure there's much of
>>>> a better option that's not pretty fragile (like putting a double in the
>>>> union instead and just assuming that's good enough). Suggestions welcome...
>>> 
>>> This doesn't seem to handle NaNs and infinities.  Also, I wonder whether you're guaranteed to get enough precision to represent the value accurately with << (printf does not guarantee this).  Will the assembler take a hex format?  That would be better.
>> 
>> My reading of the C++ standard is that << does not guarantee that the value will be printed exactly.  You need 7 digits after the decimal point in order to print all expressible immediates exactly, but you only get 6 digits.  A test on the immediate value 0x1.1p-3 seems to confirm this.
> 
> I get #1.328125e-01 for 0x1.1p-3, which seems right? Note that LLVM's output streamer is a raw_ostream, not standard C++ streams.

Yes, that's the correct value.  With "std::cout << 0x1.1p-3" I was seeing "0.132812".

- Steve