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

[Reid Spencer]

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.