[atari] Optimize fd routines (#340)

* [atari] Optimize fd routines * fixup! [atari] Optimize fd routines
llvm-mos · Jun 19, 2024 · d107f88 · d107f88
1 parent 8bc67c8
commit d107f88
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Showing 2 changed files with 10 additions and 16 deletions.
diff --git a/mos-platform/atari8-common/fdtable.s b/mos-platform/atari8-common/fdtable.s
@@ -31,22 +31,18 @@ fdtoiocb_down:
         bne     inval
         cmp     #MAX_FD_INDEX
         bcs     inval
-        tax
-        lda     fd_index,x              ; get index
         tay
-        lda     #$ff
-        sta     fd_index,x              ; clear entry
-        tya
+        lda     fd_index,y              ; get index
         asl     a                       ; create index into fd table
         asl     a
         tax
         lda     #$ff
+        sta     fd_index,y              ; clear entry
         cmp     fd_table+ft_iocb,x      ; entry in use?
         beq     inval                   ; no, return error
         lda     fd_table+ft_usa,x       ; get usage counter
         beq     ok_notlast              ; 0? (shouldn't happen)
-        sec
-        sbc     #1                      ; decr usage counter
+        sbc     #1                      ; decr usage counter, C=1
         sta     fd_table+ft_usa,x
 retiocb:php
         txa
@@ -109,8 +105,7 @@ fddecusage:
         beq     ret                     ; no, do nothing
         lda     fd_table+ft_usa,x       ; get usage counter
         beq     ret                     ; 0? should not happen
-        sec
-        sbc     #1                      ; decrement by one
+        sbc     #1                      ; decrement by one, C=1
         sta     fd_table+ft_usa,x
         bne     ret                     ; not 0
         lda     #$ff                    ; 0, table entry unused now

diff --git a/mos-platform/atari8-common/getfd.s b/mos-platform/atari8-common/getfd.s
@@ -22,17 +22,17 @@
 ; get fd_table entry in A
 ; return C = 0/1 for OK/error
 ; return fd_index entry in A if OK
+; return ft_table entry in Y (for getfd below)
 ; registers destroyed
 fdt_to_fdi:
 
         tay
         lda     #$ff
         tax
-        inx
-loop:   cmp     fd_index,x
+loop:   inx
+        cmp     fd_index,x
         beq     found
-        inx
-        cpx     #MAX_FD_INDEX
+        cpx     #MAX_FD_INDEX-1
         bcc     loop
         rts
 
@@ -48,15 +48,14 @@ found:  tya
 ; A - fd_table entry
 ; return C = 0/1 for OK/error
 ; returns fd in A if OK
-; registers destroyed, tmp1 destroyed
+; registers destroyed
 getfd:
 
-        sta     __rc10          ; save fd_table entry
         jsr     fdt_to_fdi
         bcs     error
 
         pha
-        lda     __rc10
+        tya
         asl     a
         asl     a                       ; also clears C
         tax