[llvm-commits] CVS: llvm/include/llvm/ADT/APInt.h

[Chris Lattner]

> Implement the getHighBitsSet and getLowBitsSet functions.

>    /// @param numBits the bitwidth of the result
>    /// @param hiBitsSet the number of high-order bits set in the  
> result.
>    /// @brief Get a value with high bits set
> -  static APInt getHighBitsSet(uint32_t numBits, uint32_t hiBitsSet);
> +  static APInt getHighBitsSet(uint32_t numBits, uint32_t hiBitsSet) {
> +    assert(hiBitsSet <= numBits && "Too many bits to set!");
> +    uint32_t mvBits = numBits - hiBitsSet;
> +    // For small values, return quickly
> +    if (numBits <= APINT_BITS_PER_WORD)
> +      return APInt(numBits, ((1ULL << hiBitsSet) - 1) << mvBits);

If hiBitsSet == numBIts == 64, this invokes undefined behavior.

> +    APInt Result(numBits, 1);
> +    return (APInt(numBits, 1).shl(hiBitsSet) - APInt(numBits,  
> 1)).shl(mvBits);

likewise.

> +  }
>
>    /// Constructs an APInt value that has the bottom loBitsSet bits  
> set.
>    /// @param numBits the bitwidth of the result
>    /// @param loBitsSet the number of low-order bits set in the  
> result.
>    /// @brief Get a value with low bits set
> -  static APInt getLowBitsSet(uint32_t numBits, uint32_t loBitsSet);
> +  static APInt getLowBitsSet(uint32_t numBits, uint32_t loBitsSet) {
> +    assert(loBitsSet <= numBits && "Too many bits to set!");
> +    // For small values, return quickly
> +    if (numBits <= APINT_BITS_PER_WORD)
> +      return APInt(numBits, (1ULL << loBitsSet) - 1ULL);
> +    return APInt(numBits, 1).shl(loBitsSet) - APInt(numBits, 1);

likewise.

-Chris

> +  }
>
>    /// The hash value is computed as the sum of the words and the  
> bit width.
>    /// @returns A hash value computed from the sum of the APInt words.
>
>
>
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