zasm: improve .equ duplicate detection handling

Things are a bit more straightforward now.

apps/zasm/directive.asm

@@ -122,6 +122,12 @@ handleDW:
 handleEQU:
 	call	zasmIsLocalPass	; Are we in local pass? Then ignore all .equ.
 	jr	z, .skip		; they mess up duplicate symbol detection.
+	; We register constants on both first and second pass for one little
+	; reason: .org. Normally, we'd register constants on second pass only
+	; so that we have values for forward label references, but we need .org
+	; to be effective during the first pass and .org needs to support
+	; expressions. So, we double-parse .equ, clearing the const registry
+	; before the second pass.
 	push	hl
 	push	de
 	push	bc

apps/zasm/main.asm

@@ -64,6 +64,10 @@ zasmMain:
 	call	ioPrintLN
 	xor	a
 	ld	(ZASM_FIRST_PASS), a
+	; before parsing the file for the second pass, let's clear the const
+	; registry. See comment in handleEQU.
+	ld	ix, SYM_CONST_REGISTRY
+	call	symClear
 	call	zasmParseFile
 .end:
 	jp	ioLineNo		; --> HL, --> DE, returns
@@ -209,9 +213,8 @@ _beginLocalPass:
 	; Set local pass
 	ld	(ZASM_LOCAL_PASS), a
 	; Empty local label registry
-	xor	a
-	ld	(SYM_LOC_NAMES), a
-	ret
+	ld	ix, SYM_LOCAL_REGISTRY
+	jp	symClear
 
 
 _endLocalPass:

apps/zasm/symbol.asm

@@ -169,7 +169,7 @@ symRegister:
 	push	de	; --> lvl 2. it's our value.
 
 	call	_symFind
-	jr	z, .alreadyThere
+	jr	z, .duplicateError
 
 
 	; First, let's get our strlen
@@ -223,32 +223,6 @@ symRegister:
 	pop	hl		; <-- lvl 1
 	ret
 
-.alreadyThere:
-	; We are in a tricky situation with regards to our handling of the
-	; duplicate symbol error. Normally, it should be straightforward: We
-	; only register labels during first pass and evaluate constants during
-	; the second. Easy.
-	; We can *almost* do that... but we have ".org". .org affects label
-	; values and supports expressions, which means that we have to evaluate
-	; constants during first pass. But because we can possibly have forward
-	; references in ".equ", some constants are going to have a bad value.
-	; Therefore, we really can't evaluate all constants during the first
-	; pass.
-	; With this situation, how do you manage detection of duplicate symbols?
-	; By limiting the "duplicate error" condition to the first pass. During,
-	; first pass, sure, we don't have our proper values, but we have all our
-	; symbol names. So, if we end up in .alreadyThere during first pass,
-	; then it's an error condition. If it's not first pass, then we need
-	; to update our value.
-
-	call	zasmIsFirstPass
-	jr	z, .duplicateError
-	; Second pass. Don't error out, just update value, which DE points to.
-	pop	hl		; <-- lvl 2, the value to register
-	call	writeHLinDE
-	pop	hl		; <-- lvl 1
-	cp	a		; ensure Z
-	ret
 .duplicateError:
 	pop	de		; <-- lvl 2
 	pop	hl		; <-- lvl 1
@@ -321,3 +295,15 @@ symFindVal:
 .end:
 	pop	ix
 	ret
+
+; Clear registry at IX
+symClear:
+	push	af
+	push	hl
+	ld	l, (ix)
+	ld	h, (ix+1)
+	xor	a
+	ld	(hl), a
+	pop	hl
+	pop	af
+	ret