We're on Discord! Please join our server now if you don't want to miss anything! (More info) | Join the UCC4 contest! (More info)

* WalrusIRC & Discord main room

If you have a forum account, have more than 4 posts and are not part of a restricted usergroup, then you can chat in our main Discord server room directly from here and continue using the forums at the same time. Or you can join our server directly and access many more discussion rooms!

Author Topic: Heapsort, VATSort, and ListSort  (Read 563 times)

0 Members and 1 Guest are viewing this topic.

Offline Zeda

  • New User
  • Join Date: Jun 2018
  • Location:
  • Posts: 10
  • Post Rating Ratio: +2/-0
Heapsort, VATSort, and ListSort
« on: July 04, 2018, 02:28:02 am »
Hey all, I implemented the heapsort algorithm with some features inspired by Sean McLaughlin's implementation. Heapsort operates in O(n*log(n)) time, so it is fast even as array sizes increase. The cool perk to Sean's implementation that I wanted to include in mine is the ability to have a callback function that performs comparisons. This is fantastic if your array contains pointers to, say, an array of strings. The callback function can take the inputs (in my case, HL and DE), perform a string comparison, and return the result to the heapsort routine. Heapsort will then know whether or not to swap the elements.

As an example, I created a VAT sorting routine. It creates an array of pointers to the VAT entries of named variables (like Programs, Appvars, etc.), and then uses a fancy callback function that compares the names of the VAT entries. Returned is an alphabetically sorted array of pointers.

As well, I made a very fast routine to sort TI lists. The callback routine for this takes indices, constructs pointers to the actual list data, compares them, then returns the result. Since the OS routine uses an O(n2) algorithm, my program can perform way faster on larger lists. I ran a few tests on random lists and came up with:

* at 100 elements, the OS routine and my routine were pretty close in speed.
* at 400 elements, my routine sorted it in ~1.3 seconds, versus ~9.5. for the OS routine
* at 999 elements, my routine sorted it in ~3.0 seconds, versus ~55.5. for the OS.

Code: (Heapsort) [Select]
#ifndef scrap
#define scrap 8000h
.echo "Warning, 'scrap' not defined, defining scrap=8000h"
#endif
#ifndef SMC
arraybase= scrap
arraylen = scrap+2
#endif
heapflags= 33
curchild = 0
heapsort:
;   HL points to the array data
;   BC is the size of the array. NOT GREATER THAN 32767
;   IX points to the routine that compares the values
#ifdef fast
    call heapify
    ld hl,(arraylen)
#else
    push bc
    call heapify
    pop hl
#endif
_:
    dec hl
    ld (arraylen),hl
#ifndef fast
    push hl
#endif
    ld de,(arraybase)
    add hl,hl
    inc de
    add hl,de
#ifdef fast
    ld a,(de)
    ldd
    inc hl
    ld (hl),a
    dec hl
    ld a,(de)
    ldd
    inc hl
    ld (hl),a
#else
    call swap
#endif
    ld bc,1
    call propogate
#ifdef fast
    ld hl,(arraylen)
#else
    pop hl
#endif
    ld a,h
    or l
    jr nz,-_   
    ret
heapify:
;Inputs:
;   HL points to the array data
;   BC is the size of the array. NOT GREATER THAN 32767
;   IX points to the routine that compares the values
    ld (arraybase),hl
    ld (arraylen),bc
    srl b
    rr c
_:
    push bc
    call propogate
    pop bc
    dec bc
    ld a,b
    or c
    jr nz,-_
    ret
propogate:
;BC-1 is the parent index
;2BC is the child1 index
    res curchild,(iy+heapflags)
proppost:
    sla c
    rl b
    ld d,b
    ld e,c
#ifdef SMC
arraylen=$+1
    ld hl,0
#else
    ld hl,(arraylen)
#endif
    sbc hl,de
    add hl,de
    ret c  ;no children
;compare the two children
#ifdef SMC
arraybase=$+1
    ld hl,0
#else
    ld hl,(arraybase)
#endif
    add hl,de
    add hl,de
    inc hl
    ld d,(hl)
    dec hl
    ld e,(hl)
    dec hl
    push hl
    ld a,(hl)
    dec hl
    ld l,(hl)
    ld h,a
    ;HL holds the value of child0
    ;DE holds the value of child1
    jr z,+_
    call callix
    jr nc,+_
    ex de,hl
    pop de
    inc de
    inc de
    set curchild,(iy+heapflags)
    push de
_:
;{stack} points to the child
;HL is the value of the child
;BC points to the parent
;now compare the child and parent
    ex de,hl
    ld hl,(arraybase)
    add hl,bc
    push hl
    dec hl
    ld a,(hl)
    dec hl
    ld l,(hl)
    ld h,a
    call callix
    pop hl
    pop de
    ret nc
    dec hl
    call swap
;values swapped, now set parent=child
;BC is the index of child1
    bit curchild,(iy+heapflags)
    jp z,proppost
    inc bc
    jp propogate
swap:
;HL points to the top of one word
;DE points to the top of another
;Must preserve BC
#ifdef fast
    ld a,(de)
    ldd
    inc hl
    ld (hl),a
    dec hl
    ld a,(de)
    ldd
    inc hl
    ld (hl),a
    inc c
    inc bc
#else
    call +_
_:
    ld a,(de)
    ldd
    inc hl
    ld (hl),a
    dec hl
    inc bc
#endif
    ret
callix:
    jp (ix)
Even when optimizing for speed over size, my code is smaller, but I'm fairly sure there are more optimizations to be found!



Offline Lionel Debroux

  • Full User
  • Join Date: Jan 2015
  • Location:
  • Posts: 241
  • Post Rating Ratio: +11/-0
    • debrouxl
    • 58/5891
Re: Heapsort, VATSort, and ListSort
« Reply #1 on: July 04, 2018, 04:48:26 am »
Hi Zeda :)
That's another great display that TI uses silly, slow algorithms...
That reminds me of Samuel Stearley's faster next_expression_index() and list item access routines for the TI-68k series.

Out of curiosity:
* how much execution time does inlining the comparison function save ?
* what's the execution time of an implementation of shellsort with a reasonable sequence (not the original O(n^2) one) on the same-sized lists produced from the same random seeds ? There's no O(n*log(n)) implementation of shellsort, but there's usually a range of sizes where an implementation with a reasonable sequence it trounces the quadratic sorts while being competitive with some asymptotically better O(n*log(n)) sorts. 200 items could be within that range, but 999 usually isn't.
Member of the TI-Chess Team.
Co-maintainer of GCC4TI (GCC4TI online documentation), TIEmu and TILP.
Co-admin of TI-Planet.

 


You can also use the following HTML or bulletin board code to share it on your page or forum signature!


Also do not forget to check our affiliates below.
Planet Casio TI-Planet Calc.news BroniesQC BosaikNet Velocity Games