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ed: fix bufDelLines logic
It was mostly wrong.
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@ -89,26 +89,28 @@ bufGetLine:
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; WARNING: no bounds check. The only consumer of this routine already does
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; bounds check.
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bufDelLines:
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ex de, hl
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; Let's start with setting up BC, which is (CNT-DE) * 2
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push hl ; --> lvl 1
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scf \ ccf
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sbc hl, de ; HL now has delcount -1
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inc hl ; adjust for actual delcount
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; We have the number of lines to delete in HL. We're going to move this
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; to BC for a LDIR, but before we do, there's two things we need to do:
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; adjust buffer line count and multiply by 2 (we move words, not bytes).
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push de ; --> lvl 2
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ex de, hl ; del cnt now in DE
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ld hl, (BUF_LINECNT)
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scf \ ccf
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sbc hl, de ; HL now has adjusted line cnt
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sbc hl, de
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; mult by 2 and we're done
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sla l \ rl h
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push hl \ pop bc
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pop hl ; <-- lvl 1
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; Good! BC done. Now, let's adjust BUF_LINECNT by DE-HL
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push hl ; --> lvl 1
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scf \ ccf
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sbc hl, de ; HL -> nb of lines to delete, negative
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push de ; --> lvl 2
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ld de, (BUF_LINECNT)
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add hl, de ; adding DE to negative HL
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ld (BUF_LINECNT), hl
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; Good! one less thing to think about. Now, let's prepare moving DE
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; (delcnt) to BC. But first, we'll multiply by 2.
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sla e \ rl d
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push hl \ pop bc ; BC: delcount * 2
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pop de ; <-- lvl 2
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pop hl ; <-- lvl 1
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; Line count updated!
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; let's have invert HL and DE to match LDIR's signature
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ex de, hl
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; At this point we have higher index in HL, lower index in DE and number
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; of bytes to delete in BC. It's convenient because it's rather close
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; to LDIR's signature! The only thing we need to do now is to translate
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