[cfe-dev] BitstreamReader::GetCurrentBitNo() counterintuitive

[Chris Lattner]

On Dec 23, 2008, at 12:36 AM, Zhongxing Xu wrote:

> As the comments said, BitstreamReader::GetCurrentBitNo() should  
> return the bit # of the bit we are reading. But the current  
> implementation actually return 4 more bytes than the bit we are  
> reading. It calculate the bit number by
>
> (NextChar-FirstChar)*8 + ((32-BitsInCurWord) & 31);
>
> But 'NextChar' is already after the word that we are reading. I  
> propose to fix this by the following patch.

Hi Zhongxing,

This is ok as long as it doesn't cause any regressions in the *llvm*  
dejagnu regression tests, thanks!

-Chris

>
>
> Index: include/llvm/Bitcode/BitstreamReader.h
> ===================================================================
> --- include/llvm/Bitcode/BitstreamReader.h    （版本 61317）
> +++ include/llvm/Bitcode/BitstreamReader.h    （工作副本）
> @@ -114,7 +114,8 @@
>
>    /// GetCurrentBitNo - Return the bit # of the bit we are reading.
>    uint64_t GetCurrentBitNo() const {
> -    return (NextChar-FirstChar)*8 + ((32-BitsInCurWord) & 31);
> +    return (NextChar-FirstChar-4)*8 + (BitsInCurWord ? (32- 
> BitsInCurWord) & 31
> +                                                     : 32);
>    }
>
>    /// JumpToBit - Reset the stream to the specified bit number.
> @@ -130,7 +131,6 @@
>
>      // Skip over any bits that are already consumed.
>      if (WordBitNo) {
> -      NextChar -= 4;
>        Read(static_cast<unsigned>(WordBitNo));
>      }
>    }
>
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev