Patrick.Schluter at bbox.fr
Mon Jan 7 20:06:17 UTC 2019
On Monday, 7 January 2019 at 18:56:17 UTC, H. S. Teoh wrote:
> On Mon, Jan 07, 2019 at 06:42:13PM +0000, Patrick Schluter via
> Digitalmars-d-learn wrote:
>> On Monday, 7 January 2019 at 17:23:19 UTC, Michelle Long wrote:
>> > Is there any direct way to convert a signed nibble in to a
>> > signed byte with the same absolute value? Obviously I can do
>> > some bit comparisons but just curious if there is a very
>> > quick way.
>> byte b = nibble | ((nibble & 0x40)?0xF0:0);
> This is equivalent to doing a bit comparison (implied by the ?
> operator). You can do it without a branch:
> cast(byte)(nibble << 4) >> 4
> will use the natural sign extension of a (signed) byte to
> "stretch" the upper bit. It just takes 2-3 CPU instructions.
Yeah, my bit-fiddle-fu goes back to pre-barrel-shifter days. Up
to 32 bit processors, shifting was more expensive than branching.
More information about the Digitalmars-d-learn