Author: Robert Hyatt
Date: 06:58:54 03/08/99
Go up one level in this thread
On March 08, 1999 at 02:53:58, David Blackman wrote: >On March 08, 1999 at 01:36:56, Peter McKenzie wrote: > >>On March 07, 1999 at 23:37:39, Peter McKenzie wrote: >> >>>On March 07, 1999 at 23:29:31, Stuart Cracraft wrote: >>> >>>>Crafty seems to have a Scale_Up/Scale_Down factor and I'm curious >>>>if Bob would talk a little about this. Seems costly to add a memory >>>>reference and a division (?). >>> >>>I'm guess his divisions are usually by a constant that is a multiple of 2, in >> >>oops, I meant power of 2 ... >> >>>which case the compiler will just do a bit shift. > >Not if you're using signed integers. The way the IEEE recommends to do signed >integer division and the way most chips and compilers do it is to round towards >0. Right shift rounds towards -infinity. Because of the difference, most >compilers don't do this optimisation for signed numbers. > >Of course Bob might use unsigned integers here. I haven't looked at his code. I don't follow. positive ints approach zero with right shifts. Negative ints approach -1 with right shifts, since most processors that I know of have both logical _and_ arithmetic (sign preserving) shifts... the only glitch is that -1 >> 1 is not zero. But I am not doing this kind of stuff anyway... I am going indirect through an array to scale values.
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