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asm_routines: update lz4 comments

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This commit is contained in:
Vince Weaver 2018-02-21 16:11:29 -05:00
parent ae638b8a37
commit da04382c18
1 changed files with 34 additions and 24 deletions
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58
asm_routines/lz4_decode.s
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@ -72,7 +72,7 @@ lz4_decode:
unpmain:
ldy #0 ; used to index
ldy #0 ; used to index, always zero
parsetoken:
jsr getsrc ; get next token
@ -83,12 +83,15 @@ parsetoken:
lsr
lsr
beq copymatches ; if zero, then no literals
; jump ahead and copy
jsr buildcount
tax
jsr docopy
lda src
cmp end
jsr buildcount ; add up all the literal sizes
; result is in ram[count+1]-1:A
tax ; now in ram[count+1]-1:X
jsr docopy ; copy the literals
lda src ; 16-bit compare
cmp end ; to see if we have reached the end
lda src+1
sbc end+1
bcs done
@ -103,45 +106,51 @@ copymatches:
and #$0f ; get bottom 4 bits
; match count. 0 means 4
; 15 means 19+, must be calculated
jsr buildcount
jsr buildcount ; add up count bits, in ram[count+1]-:A
clc
adc #4 ; adjust count by 4 (minmatch)
tax
beq copy_skip ; BUGFIX
bcc copy_skip
tax ; now in ramp[count+1]-1:X
inc count+1
copy_skip:
lda src+1
beq copy_no_adjust ; BUGFIX, don't increment if
; exactly a multiple of 0x100
bcc copy_no_adjust
inc count+1 ; increment if we overflowed
copy_no_adjust:
lda src+1 ; save src on stack
pha
lda src
pha
sec
lda dst
sec ; subtract delta
lda dst ; from destination, make new src
sbc delta
sta src
lda dst+1
sbc delta+1
sta src+1
jsr docopy
pla
jsr docopy ; do the copy
pla ; restore the src
sta src
pla
sta src+1
jmp parsetoken
jmp parsetoken ; back to parsing tokens
done:
pla
rts
;=========
; getsrc
;=========
; gets byte from src into A, increments pointer
getsrc:
lda (src), Y ; get a byte from src
inc src ; increment pointer
@ -183,10 +192,11 @@ getput:
;=============
; putdst
;=============
; store A into destination
putdst:
sta (dst), Y
inc dst
bne putdst_end
sta (dst), Y ; store A into destination
inc dst ; increment 16-bit pointer
bne putdst_end ; if overflow, increment top byte
inc dst+1
putdst_end:
rts