🚀 go-pugleaf

In article <15665@winchester.mips.COM> rogerk@mips.COM (Roger B.A. Klorese) writes:
>In article <37515@bbn.COM> slackey@BBN.COM (Stan Lackey) writes:
>>The MICROvax architecture does NOT include
>>string instructions, other than MOVC3 (and MOVC5?).  Some DEC-supplied
>>software includes emulation to ease the transition.  Generating the
>>in-line emulation using a reduced instruction set is NO PROBLEM, right?

>There *IS NO* MicroVAX architecture.  There is a MicroVAX *implementation*
>of the VAX architecture, which implements some instructions in software.
>This is very different.

>>1.  The uVAX is NOT said to implement the VAX architecture.

>I've never seen this claimed.

   To quote from "VAX MACRO and Instruction Set Reference Manual",
   page 9-126, "Character String Instructions--LOCC":

      This instruction is not part of the MicroVAX 
      architecture definition.

   This notice appears at the bottom of each page which describes an
   instruction not in the MicroVAX architecture.


   Since we are on this topic, here is a little experiment I ran.

   I wrote a version of the C function strlen (which basically looks for
   a byte of 0x00) which does not use the LOCC (locate character instruction),
   but rather uses the trick:

	    ((x - 0x01010101) & ~x) & 0x80808080) != 0)

   to scan 4 characters at a time for the null-byte, it basically looks
   like:

	    MOVL    4(AP),R0                ; address of string (arg 1) in R0
      5$:   SUBL3   #^x01010101,(R0),R1     ; R1 = *string - 0x01010101
	    BICL2   (R0)+,R1                ; R1 = R1 & ~*string++
	    BICL2   #^x7F7F7F7F,R1          ; R1 = R1 & 0x80808080
	    BEQL    5$                      ; all 4 bytes are non-zero
	    BBS     #7,R1,10$               ; low order byte was 0
	    BBS     #15,R1,11$              ; second byte was 0
	    BBS     #23,R1,12$              ; third bytes was 0
	    SUBL2   #1,R0                   ; high byte was 0, adjust
	    SUBL2   4(AP),R0                ; length = end-start-adjust
	    RET
      10$:  SUBL2   #2,R0                   ; adjust, etc....


   Anyway here are some results compared with the "VAXC" strlen:

   I had a for loop which did 10 strlens/mystrlens, which was repeated
   x times based on the length of the string l:

	   x = (l <    10) ? 10000 :
	       (l <   100) ?  1000 :
	       (l <  1000) ?   100 :
	       (l < 10000) ?    10 : 1;

               
                 ----------------- string lengths --------------
  machine  vers      0      1      9     99    999   9999  99999
  -------  ----  -----  -----  -----  -----  -----  -----  -----
  VS2000   VAXC   9.16   9.51  12.04   4.03   3.28   3.14   3.17
	   MINE   2.42   2.52   3.41   1.31   1.13   1.12   1.13

  6220     VAXC    .89    .98   1.26    .53    .42    .44    .43
	   MINE    .92    .96   1.29    .51    .40    .42    .45

  11/780   VAXC   3.02   2.98   3.23    .70    .39    .51    .58
	   MINE   2.54   2.68   3.50   1.32   1.08   1.16   1.24

  11/785   VAXC   2.27   2.30   2.40    .33    .24    .23    .39
	   MINE   1.97   2.11   2.44    .72    .69    .70    .90

    (all were VMS5.0-2 except my vaxstation which is VMS4.7)

    Since the VS2000 is just a uVAXII, it obviously emulates the LOCC
    which is in strlen, but what about the 6220?  Does it?  In four
    cases the 11/785 (and once the 11/780) toasted the 6220!

    Perhaps I should try a simple:

	5$:  TSTB  (R1)+
	     BNEQ  5$

    as well.


    For what it's worth,
    John Hascall