value range propagation for _bitwise_ OR

[Ellery Newcomer]

On 12/04/2010 01:21 PM, Ellery Newcomer wrote:
> is it just me, or does this fail for
>
> minA = 0
> minB = 0
> maxA = 0x80_00_00_00
> maxB = 0x80_00_00_00
>
> I'm pretty sure you need to handle 1<<  32 specially

i'm thinking this is better:

uint32_t maxOr (uint32_t minA, uint32_t minB,
         uint32_t maxA, uint32_t maxB)
{
     assert (minA <= maxA);
     assert (minB <= maxB);

     if (maxA == 0) return maxB;
     if (maxB == 0) return maxA;

     uint32_t a = maxA ^ minA;
     if (a != 0) {
         a |= (1 << highbit (a)) - 1;
         a = a & maxA & maxB;
         if (a != 0)
             a = (1 << highbit (a)) - 1;
     }

     uint32_t b = maxB ^ minB;
     if (b != 0) {
	b |= (1 << highbit (b)) - 1;
         b = b & maxA & maxB;
         if (b != 0)
             b = (1 << highbit (b)) - 1;
     }

     return maxA|maxB|a|b;
}