[llvm-commits] CVS: llvm/include/llvm/Support/MathExtras.h

[Reid Spencer]

Jim,

Is this going to work okay on all platforms? (see below)

On Wed, 2005-08-17 at 12:28 -0500, Jim Laskey wrote:
> 
> Changes in directory llvm/include/llvm/Support:
> 
> MathExtras.h updated: 1.23 -> 1.24
> ---
> Log message:
> 
> Added support for converting raw bits to FP, and FP to raw bits.  The intent
> is to avoid the distraction of the union declarations.
> 
> 
> 
> ---
> Diffs of the changes:  (+44 -0)
> 
>  MathExtras.h |   44 ++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 44 insertions(+)
> 
> 
> Index: llvm/include/llvm/Support/MathExtras.h
> diff -u llvm/include/llvm/Support/MathExtras.h:1.23 llvm/include/llvm/Support/MathExtras.h:1.24
> --- llvm/include/llvm/Support/MathExtras.h:1.23	Wed Aug  3 15:53:19 2005
> +++ llvm/include/llvm/Support/MathExtras.h	Wed Aug 17 12:27:47 2005
> @@ -168,6 +168,50 @@
>      return 63 - CountLeadingZeros_64(Value);
>  }
>  
> +// BitsToDouble - This function takes a 64-bit integer and returns the bit
> +// equivalent double.
> +inline double BitsToDouble(uint64_t Bits) {
> +  union {
> +    uint64_t L;
> +    double D;
> +  } T;
> +  T.L = Bits;
> +  return T.D;
> +}

This one should be fine because double and uint64_t are 64-bits on all
platforms we care about.

> +
> +// BitsToFloat - This function takes a 32-bit integer and returns the bit
> +// equivalent float.
> +inline float BitsToFloat(unsigned Bits) {
> +  union {
> +    unsigned I;
> +    float F;
> +  } T;
> +  T.I = Bits;
> +  return T.F;
> +}

This one I'm not so sure about. "unsigned" could be 32 or 64-bits
depending on the platform. float is probably 32-bits on all platforms we
care about. If unsigned is 64-bits and big-endian, we would get the
wrong value for the float as it would be effectively shifted into the
high order bits. Truncation could occur too.

Shouldn't this use uin32_t instead of "unsigned" ?


> +
> +// DoubleToBits - This function takes a double and returns the bit
> +// equivalent 64-bit integer.
> +inline uint64_t DoubleToBits(double Double) {
> +  union {
> +    uint64_t L;
> +    double D;
> +  } T;
> +  T.D = Double;
> +  return T.L;
> +}

This should be okay.

> +
> +// FloatToBits - This function takes a float and returns the bit
> +// equivalent 32-bit integer.
> +inline unsigned FloatToBits(float Float) {
> +  union {
> +    unsigned I;
> +    float F;
> +  } T;
> +  T.F = Float;
> +  return T.I;
> +}

This one suffers same problem as for BitsToFloat

Reid
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