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

[Reid Spencer]

On Thu, 2007-03-22 at 12:35 -0700, Jeff Cohen wrote:
> How is it any worse than checking for GCC?

I don't like that either :)

> 
> It's treated as an intrinsic when optimizations are enable.  It directly 
> generates a bswap instruction.  Same as the conditional code for GCC.

Okay, sounds like its worth providing this.

> 
> Reid Spencer wrote:
> > Jeff,
> >
> > On Thu, 2007-03-22 at 14:12 -0500, Jeff Cohen wrote:
> >   
> >> Changes in directory llvm/include/llvm/Support:
> >>
> >> MathExtras.h updated: 1.43 -> 1.44
> >> ---
> >> Log message:
> >>
> >> Be more explicit concerning argument sizes.
> >> Use VC++ byteswap intrinsics.
> >>     
> >
> > ... snip ...
> >
> >   
> >> @@ -93,22 +93,30 @@
> >>  
> >>  /// ByteSwap_16 - This function returns a byte-swapped representation of the
> >>  /// 16-bit argument, Value.
> >> -inline unsigned short ByteSwap_16(unsigned short Value) {
> >> -  unsigned short Hi = Value << 8;
> >> -  unsigned short Lo = Value >> 8;
> >> +inline uint16_t ByteSwap_16(uint16_t Value) {
> >> +#if defined(_MSC_VER) && !defined(_DEBUG)
> >> +  // The DLL version of the runtime lacks these functions (bug!?), but in a
> >> +  // release build they're replaced with BSWAP instructions anyway.
> >> +  return _byteswap_ushort(Value);
> >> +#else
> >> +  uint16_t Hi = Value << 8;
> >> +  uint16_t Lo = Value >> 8;
> >>    return Hi | Lo;
> >> +#endif
> >>  }
> >>     
> >
> > Pedantically, such an ifdef is not allowed to occur in this header file.
> > It can only occur in lib/System. LLVM is supposed to be platform/machine
> > agnostic everywhere except lib/System. Is there a real advantage to
> > using _byteswap_ushort? Seems to me that the function call overhead
> > would negate any speed advantage. Is this thing inline? I would prefer
> > that we just leave the code as is. If you really feel its necessary to
> > do this for release versions, please create an inline function in
> > lib/System that works for all platforms.
> >
> >   
> >>  
> >>  /// ByteSwap_32 - This function returns a byte-swapped representation of the
> >>  /// 32-bit argument, Value.
> >> -inline unsigned ByteSwap_32(unsigned Value) {
> >> +inline uint32_t ByteSwap_32(uint32_t Value) {
> >>     
> > The type change is fine, but ..
> >   
> >>  #if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)
> >>  	return __builtin_bswap32(Value);
> >> +#elif defined(_MSC_VER) && !defined(_DEBUG)
> >> +  return _byteswap_ulong(Value);
> >>     
> > I really don't like this unless you put this in lib/System.
> >   
> >>  #else
> >> -  unsigned Byte0 = Value & 0x000000FF;
> >> -  unsigned Byte1 = Value & 0x0000FF00;
> >> -  unsigned Byte2 = Value & 0x00FF0000;
> >> -  unsigned Byte3 = Value & 0xFF000000;
> >> +  uint32_t Byte0 = Value & 0x000000FF;
> >> +  uint32_t Byte1 = Value & 0x0000FF00;
> >> +  uint32_t Byte2 = Value & 0x00FF0000;
> >> +  uint32_t Byte3 = Value & 0xFF000000;
> >>    return (Byte0 << 24) | (Byte1 << 8) | (Byte2 >> 8) | (Byte3 >> 24);
> >>  #endif
> >>  }
> >> @@ -118,9 +126,11 @@
> >>  inline uint64_t ByteSwap_64(uint64_t Value) {
> >>  #if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)
> >>  	return __builtin_bswap64(Value);
> >> +#elif defined(_MSC_VER) && !defined(_DEBUG)
> >> +  return _byteswap_uint64(Value);
> >>     
> >
> > Same deal.
> >
> >   
> >>  #else
> >> -  uint64_t Hi = ByteSwap_32(unsigned(Value));
> >> -  uint64_t Lo = ByteSwap_32(unsigned(Value >> 32));
> >> +  uint64_t Hi = ByteSwap_32(uint32_t(Value));
> >> +  uint32_t Lo = ByteSwap_32(uint32_t(Value >> 32));
> >>    return (Hi << 32) | Lo;
> >>  #endif
> >>  }
> >> @@ -129,7 +139,7 @@
> >>  /// counting the number of zeros from the most significant bit to the first one
> >>  /// bit.  Ex. CountLeadingZeros_32(0x00F000FF) == 8.
> >>  /// Returns 32 if the word is zero.
> >> -inline unsigned CountLeadingZeros_32(unsigned Value) {
> >> +inline unsigned CountLeadingZeros_32(uint32_t Value) {
> >>    unsigned Count; // result
> >>  #if __GNUC__ >= 4
> >>    // PowerPC is defined for __builtin_clz(0)
> >> @@ -142,7 +152,7 @@
> >>    Count = 0;
> >>    // bisecton method for count leading zeros
> >>    for (unsigned Shift = 32 >> 1; Shift; Shift >>= 1) {
> >>     
> >
> > Why not uint32_t for Shift?
> >
> >   
> >> -    unsigned Tmp = Value >> Shift;
> >> +    uint32_t Tmp = Value >> Shift;
> >>      if (Tmp) {
> >>        Value = Tmp;
> >>      } else {
> >> @@ -170,7 +180,7 @@
> >>      if (!Value) return 64;
> >>      Count = 0;
> >>      // bisecton method for count leading zeros
> >> -    for (uint64_t Shift = 64 >> 1; Shift; Shift >>= 1) {
> >> +    for (unsigned Shift = 64 >> 1; Shift; Shift >>= 1) {
> >>     
> >
> > Why not uint32_t? For conformity with the rest of your changes?
> >
> >   
> >>        uint64_t Tmp = Value >> Shift;
> >>        if (Tmp) {
> >>          Value = Tmp;
> >> @@ -180,7 +190,7 @@
> >>      }
> >>    } else {
> >>      // get hi portion
> >> -    unsigned Hi = Hi_32(Value);
> >> +    uint32_t Hi = Hi_32(Value);
> >>  
> >>      // if some bits in hi portion
> >>      if (Hi) {
> >> @@ -188,7 +198,7 @@
> >>          Count = CountLeadingZeros_32(Hi);
> >>      } else {
> >>          // get lo portion
> >> -        unsigned Lo = Lo_32(Value);
> >> +        uint32_t Lo = Lo_32(Value);
> >>          // same as 32 bit value
> >>          Count = CountLeadingZeros_32(Lo)+32;
> >>      }
> >> @@ -201,7 +211,7 @@
> >>  /// counting the number of zeros from the least significant bit to the first one
> >>  /// bit.  Ex. CountTrailingZeros_32(0xFF00FF00) == 8.
> >>  /// Returns 32 if the word is zero.
> >> -inline unsigned CountTrailingZeros_32(unsigned Value) {
> >> +inline unsigned CountTrailingZeros_32(uint32_t Value) {
> >>  #if __GNUC__ >= 4
> >>    return Value ? __builtin_ctz(Value) : 32;
> >>  #else
> >> @@ -262,7 +272,7 @@
> >>  /// Log2_32 - This function returns the floor log base 2 of the specified value, 
> >>  /// -1 if the value is zero. (32 bit edition.)
> >>  /// Ex. Log2_32(32) == 5, Log2_32(1) == 0, Log2_32(0) == -1, Log2_32(6) == 2
> >> -inline unsigned Log2_32(unsigned Value) {
> >> +inline unsigned Log2_32(uint32_t Value) {
> >>    return 31 - CountLeadingZeros_32(Value);
> >>  }
> >>  
> >> @@ -275,7 +285,7 @@
> >>  /// Log2_32_Ceil - This function returns the ceil log base 2 of the specified
> >>  /// value, 32 if the value is zero. (32 bit edition).
> >>  /// Ex. Log2_32_Ceil(32) == 5, Log2_32_Ceil(1) == 0, Log2_32_Ceil(6) == 3
> >> -inline unsigned Log2_32_Ceil(unsigned Value) {
> >> +inline unsigned Log2_32_Ceil(uint32_t Value) {
> >>    return 32-CountLeadingZeros_32(Value-1);
> >>  }
> >>     
> >
> > Reid.
> >
> >
> >
> >
> >   
>