llvm dev - Jun 2008 - [LLVMdev] rounding mode

Hello LLVMers,

 

A question.  In our system we often go from 

 

our-system -> LLVM generated functions -> callback functions in our
system

 

Is it the case that we can rely on the rounding mode being the same on
both sides of the LLVM generated functions or can generated functions
change the rounding mode and not restore it prior to calling another
function which may or may not be one generated via LLVM?  In our system,
all our APFloats use the default rounding mode.

 

Thanks,

Chuck.

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On Jun 24, 2008, at 11:58 AM, Chuck Rose III wrote:
> Hello LLVMers,
>
> A question.  In our system we often go from
>
> our-system -> LLVM generated functions -> callback functions in our  
> system
>
> Is it the case that we can rely on the rounding mode being the same  
> on both sides of the LLVM generated functions or can generated  
> functions change the rounding mode and not restore it prior to  
> calling another function which may or may not be one generated via  
> LLVM?  In our system, all our APFloats use the default rounding mode.
Hey Chuck,

The rounding mode is part of the platform ABI and LLVM conforms to  
it.  The ABI specifies that the rounding mode is always set to default  
on entry/exit of functions.  You can be sure that if llvm changes the  
rounding mode (e.g. in certain int <-> fp conversions) that it changes  
it back before calling a function or returning.

-Chris
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