Applied patch #2762516

[fw/sdcc] / doc / choices.txt

diff --git a/doc/choices.txt b/doc/choices.txt
index 9fa79244d309fd21e6a9d491a227ded83bbf179e..1442eca452e5bed8306897b5062f5c87fce84d0b 100644 (file)
--- a/doc/choices.txt
+++ b/doc/choices.txt
@@ -105,5 +105,138 @@ Things get better when you access the same set over, as you get rid
 of the setup.  But they get worse when both ops are on the stack/in
 direct space.  Easiest this way for now.  iy may benifit...
 
-       
- 
+cmpGt:
+       ld      l,#0x80         ; 7
+       ld      a,-1(ix)        ; 19
+       xor     a,#0x80         ; 7
+       ld      h,a             ; 4
+       ld      a,#0x02         ; 7
+       sub     a,-2(ix)        ; 19
+       ld      a,l             ; 4
+       sbc     a,h             ; 4 = 71
+
+vs
+        ld      hl,0x8002      ; 10
+        ld      a,-2(ix)       ; 19
+        xor     0x80           ; 7
+        ld      d,a            ; 4
+        ld      e,-1(ix)       ; 19
+        sbc     hl,de          ; 15 = 74
+
+Why is there the whole xor thing going on?
+
+cmpGt using sub:
+        left    right   l-r    c       expect
+        0       0       0       0       false
+        -1      0       -1     0       false
+        1       0       1       0       true
+        0       -1      1       1       true
+        0       1       -1      1       false
+
+With top most bits xored
+        80h     80h     0       0      false
+        7fh     80h     FFh     1       false
+        81h     80h     01h     0       true
+        80h     7fh     01h     0       true
+        80h     81h     FFh     1       false
+
+r-l instead - ah.
+        80h     80h     0       0      false
+        7fh     80h     01h     0       false
+        81h     80h     FFh     1       true
+        80h     7fh     FFh     1       true
+        80h     81h     01h     0       false
+
+How about using the sign bit and no XOR on r-l?
+        0       0        0              false
+        FFh     0       01h            false
+        01h     0        FFh            true
+        0       FFh      FFh            true
+        0       01h      01h            false  - works
+
+cmpEq:
+        ld      hl,#nn         ; 10
+       ld      c,(ix+-5)       ; 19
+       ld      b,(ix+-4)       ; 19
+       or      a               ; 4
+       sbc     hl,bc           ; 15
+       jp      nz,l19          ; 10 = 77
+
+       ld      a,-82(ix)       ; 19
+       cp      a,#0x01         ; 7
+       jp      nz,00129$       ; 10
+       ld      a,-81(ix)       ; 19
+       or      a,a             ; 7
+       jp      nz,00129$       ; 10 - 72
+
+Add:
+       ld      a,c             ; 4
+       add     a,#0x04         ; 7
+       ld      -4(ix),a        ; 19
+       ld      a,b             ; 4
+       adc     a,#0x00         ; 7
+       ld      -3(ix),a        ; 19 = 60
+vs
+        ld      hl,#4           ; 10
+        add     hl,bc           ; 11
+        ld      -4(ix),l        ; 19
+        ld      -3(ix),h        ; 19 = 59
+
+Same argument as above - not worth the extra cycle.
+
+Pending optimisations:
+        iTemp1 = @iTemp2
+        iTemp3 = iTemp1
+
+        iTemp4 = something in direct space
+        ...
+        push    iTemp4
+
+Swaps:
+        ld      hl,bc           ; 8
+        ld      bc,de           ; 8
+        ld      de,hl           ; 8
+
+vs
+        push    bc             ; 11
+        ld      bc,de           ; 8
+        pop     de              ; 11
+
+Swaps 2:
+        ld      a,h
+        ld      h,b
+        ld      b,a
+        ld      a,l
+        ld      l,c
+        ld      c,aq            ; 6*4 = 24
+
+Cleaning up the arguments to a call:
+         ld     iy,#n           ; 14
+         add    iy,sp           ; 15
+         ld     sp,iy           ; 10 = 39
+
+         pop    af              ; 5/byte
+
+
+So for 8 bytes and above use the first form.
+
+Pointer assign:
+        ld      hl,bc           ; 4+4
+        ld      e,(hl)          ; 7
+        inc     hl              ; 6
+        ld      d,(hl)          ; 7
+
+vs:
+        ld      a,(bc)          ; 7
+        ld      e,a             ; 4
+        inc     bc              ; 6
+        ld      a,(bc)          ; 7
+        ld      d,a             ; 4
+
+Same cost.  Not worth it, although is does free up HL.
+
+Shift left signed on HL
+      sla  l
+      rl   h                    ; 8+8 = 16
+
+      add  hl,hl                ; 11