Floating Point-The Results Are In!

Ed G. edgee at cyberpass.net
Tue May 12 12:21:12 AEST 1998


> I don't know what the code above is intended to do, but it's not
> floating point.  At the very best, it would indicate the use of the
> floating point registers for straightforward data moves.  I stand by
> my assertion that tar doesn't use floating point, neither in the
> Seventh Edition nor elsewhere.

I agree:  tar doesn't *use* floating point.  

However, from what I can determine the floating point ops in tar are
not some weird way of moving data around, nor is floating point
being used to do long arithmetic as some have suggested.

Compare the first few tar floating point ops with a dummy program 
consisting of a single call to scanf:

tar, 106 floating point ops:

0:  SETD   ;170011 
20532:  STCFD F0,(R1)   ;176011 
20562:  STF F0,(R1)   ;174011 
22406:  LDF F0,(R4)+   ;172424 
22410:  STF F0,-(SP)   ;174046 
22460:  LDF F0,(R4)+   ;172424 
22462:  STF F0,-(SP)   ;174046 
22620:  LDF F0,(R4)+   ;172424 
22622:  STF F0,-(SP)   ;174046 
24124:  LDF F0,4(R5)   ;172465 000004 
24130:  STF F0,-(SP)   ;174046 
26616:  LDF F0,#56200   ;172427 056200 
26622:  STF F0,177732(R5)   ;174065 177732 
etc.

scanf, 106 floating point ops:

000000:  SETD   ;170011 
002764:  STCFD F0,(R1)   ;176011 
003014:  STF F0,(R1)   ;174011 
004346:  LDF F0,(R4)+   ;172424 
004350:  STF F0,-(SP)   ;174046 
004420:  LDF F0,(R4)+   ;172424 
004422:  STF F0,-(SP)   ;174046 
004560:  LDF F0,(R4)+   ;172424 
004562:  STF F0,-(SP)   ;174046 
004750:  LDF F0,4(R5)   ;172465 000004 
004754:  STF F0,-(SP)   ;174046 
006410:  LDF F0,#56200   ;172427 056200 
006414:  STF F0,177732(R5)   ;174065 177732 

So it would appear that whatever floating point there is in tar comes 
from library routines which have been linked in, but which tar does 
not use.

"When you hear hoofbeats, think horses, not zebras."

Ed

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