PIC Math - the need for speed

[Darrel Taylor]

I determined it was 48 cycles by using this procedure ...

instruction execution time
http://www.picbasic.co.uk/forum/showthread.php?t=365

I've double checked, and it's definately 48. Although my hardware is different, 18F452 @ 20Mhz, it shouldn't make that much difference.

For your test routine I get these results:

Value = 20000
Start:                     ' Cycles   uS@20mhz
    PORTD.0 = 1            '    1         .2
    Delay = Value /*$004D  '   48        9.6
    PORTD.0 = 0            '    1         .2
    PauseUs 700            ' 3501      700.2   
Goto Start                 '    2         .4
                             -----     -----
              ' Loop Total   3553      710.6

And, this I didn't expect. Here's the results from Ingvar's first example

                            ' Cycles   uS@20mhz
Dummy1 = OldPulseTime >> 2  '  31        6.2
Delay = Dummy1 >> 2         '  31        6.2
Delay = Delay + Dummy1      '   4         .8
                             -----     -----
              '      Total     66       13.2

But, his second one looks pretty quick. As long as .3125 is close enough.

                            ' Cycles   uS@20mhz
Dummy1 = OldPulseTime >> 1  '   5        1.0
Dummy1 = Dummy1 >> 1        '   3         .6
Delay = Dummy1 >> 1         '   5        1.0
Delay = Delay >> 1          '   3         .6
Delay = Delay + Dummy1      '   4         .8
                             -----     -----
              '      Total     20        4.0