addHL and subHL affect flags, and are smaller (#30)

* addHL and subHL affect flags, and are smaller

Most importantly, addHL and subHL now affect the flags as you would expect from a 16 bit addition/subtraction. This seems like it'd be preferred behaviour, however I realise any code relying on it not affecting flags would break. One byte saved in addHL, and two bytes saved in subHL. Due to the branching nature of the original code, it's difficult to compare speeds, subHL is either 1 or 6 cycles faster depending on branching, and addHL is between -1 and 3 cycles faster. If the chance of a carry is 50%, addHL is expected to be a cycle faster, but for a chance of carry below 25% (so a < 0x40) this will be up to a cycle slower.

* Update core.asm

* Reworked one use of addHL

By essentially inlining both addHL and cpHLDE, 100 cycles are saved, but due to the registers not needing preserving, a byte is saved too.

* Corrected spelling error in comment

* Reworked second use of addHL

43 cycles saved, and no more addHL in critical loops. No bytes saved or used.

* Fixed tabs and spacing, and made a comment clearer.

* Clearer comments

* Adopted push/pop notation

apps/zasm/README.md

@@ -152,4 +152,11 @@ allowed. An included file cannot have an `.inc` directive.
           in the argument in the currently active filesystem and outputs its
           contents directly.
 
+## Undocumented instructions
+
+`zasm` doesn't support undocumented instructions such as the ones that involve
+using `IX` and `IY` as 8-bit registers. We used to support them, but because
+this makes our code incompatible with Z80-compatible CPUs such as the Z180, we
+prefer to avoid these in our code.
+
 [libz80]: https://github.com/ggambetta/libz80

apps/zasm/instr.asm

@@ -109,7 +109,7 @@ getInstID:
 	ret
 
 ; Parse the string at (HL) and check if it starts with IX+, IY+, IX- or IY-.
-; Sets Z if yes, unset if no.
+; Sets Z if yes, unset if no. On success, A contains either '+' or '-'.
 parseIXY:
 	push	hl
 	ld	a, (hl)
@@ -180,13 +180,15 @@ parseArg:
 	ld	a, 'N'
 	jr	.end
 .withParens:
+	ld	b, 0		; make sure it doesn't hold '-'
 	ld	c, 'M'		; C holds the argspec type until we reach
 				; .numberInParens
 	; We have parens. First, let's see if we have a (IX+d) type of arg.
 	call	parseIXY
 	jr	nz, .parseNumberInParens	; not I{X,Y}. just parse number.
 	; We have IX+/IY+/IX-/IY-.
-	; note: the "-" part isn't supported yet.
+	; A contains either '+' or '-'. Save it for later, in B.
+	ld	b, a
 	inc	hl	; (HL) now points to X or Y
 	ld	a, (hl)
 	call	upcase
@@ -202,6 +204,22 @@ parseArg:
 	call	.maybeParseExpr
 	jr	nz, .nomatch
 	; We have a proper number in parens. Number in IX
+	; is '-' in B? if yes, we need to negate the low part of IX
+	ld	a, b
+	cp	'-'
+	jr	nz, .dontNegateIX
+	; we need to negate the low part of IX
+	; TODO: when parsing routines properly support unary negative numbers,
+	; We could replace this complicated scheme below with a nice hack where
+	; we start parsing our displacement number at the '+' and '-' char.
+
+	; HL isn't needed anymore and can be destroyed.
+	push	ix \ pop hl
+	ld	a, l
+	neg
+	ld	l, a
+	push	hl \ pop ix
+.dontNegateIX:
 	ld	a, c	; M, x, or y
 	jr	.end
 .nomatch:

apps/zasm/symbol.asm

@@ -110,12 +110,14 @@ symRegister:
 	; Is our new name going to make us go out of bounds?
 	push	hl		; --> lvl 2
 	push	de		; --> lvl 3
+	ld 	d, 0
+	ld 	e, c
+	add 	hl, de		; if carry set here, sbc will carry too	
 	ld	e, (ix+2)	; DE --> pointer to record list, which is also
 	ld	d, (ix+3)	; the end of names pool
 	; DE --> names end
-	ld	a, c
-	call	addHL
-	call	cpHLDE
+	
+	sbc	hl, de		; compares hl and de destructively
 	pop	de		; <-- lvl 3
 	pop	hl		; <-- lvl 2
 	jr	nc, .outOfMemory	; HL >= DE
@@ -190,9 +192,15 @@ _symFind:
 	jr	z, .end		; match! Z already set, IY and HL placed.
 .skip:
 	; ok, next!
-	ld	a, (iy)		; name len again
-	call	addHL		; advance HL by A chars
-	inc	iy \ inc iy \ inc iy
+	
+	push 	de		; --> lvl 1
+	ld 	de, 0x0003
+	add 	iy, de		; faster and shorter than three inc's
+	ld 	e, (iy-3)	; offset is also compulsory, so no extra bytes used	
+	; (iy-3) holds the name length of the string just processed
+	add 	hl, de	; advance HL by (iy-3) characters
+	pop	de		; <-- lvl 1
+
 	djnz	.loop
 	; end of the chain, nothing found
 .nothing:

kernel/core.asm

@@ -53,28 +53,25 @@ intoIX:
 	ret
 
 ; add the value of A into HL
+; affects carry flag according to the 16-bit addition, Z, S and P untouched.
 addHL:
-	push	af
-	add	a, l
-	jr	nc, .end	; no carry? skip inc
-	inc	h
-.end:
-	ld	l, a
-	pop	af
+	push	de
+	ld 	d, 0
+	ld	e, a
+	add	hl, de
+	pop	de
 	ret
 
+
 ; subtract the value of A from HL
+; affects flags according to the 16-bit subtraction.
 subHL:
-	push	af
-	; To avoid having to swap L and A, we sub "backwards", that is, we add
-	; a NEGated value. This means that the carry flag is inverted
-	neg
-	add	a, l
-	jr	c, .end		; if carry, no carry. :)
-	dec	h
-.end:
-	ld	l, a
-	pop	af
+	push	de
+	ld	d, 0
+	ld	e, a
+	or 	a		;reset carry flag
+	sbc	hl, de		;There is no 'sub hl, de', so we must use sbc
+	pop	de
 	ret
 
 ; Compare HL with DE and sets Z and C in the same way as a regular cp X where

tools/tests/zasm/allinstrs.asm

@@ -48,14 +48,22 @@ ADD IY, IY
 ADD IY, SP
 ADD A, (IX)
 ADD A, (IX+1)
+ADD A, (IX-1)
 ADD A, (IX+10)
+ADD A, (IX-10)
 ADD A, (IX+100)
+ADD A, (IX-100)
 ADD A, (IX+127)
+ADD A, (IX-127)
 ADD A, (IY)
 ADD A, (IY+1)
+ADD A, (IY-1)
 ADD A, (IY+10)
+ADD A, (IY-10)
 ADD A, (IY+100)
+ADD A, (IY-100)
 ADD A, (IY+127)
+ADD A, (IY-127)
 AND (HL)
 AND B
 AND C
@@ -73,46 +81,78 @@ AND 32
 AND 64
 AND 128
 AND (IX+1)
+AND (IX-1)
 AND (IX+10)
+AND (IX-10)
 AND (IX+100)
+AND (IX-100)
 AND (IX+127)
+AND (IX-127)
 AND (IY+1)
+AND (IY-1)
 AND (IY+10)
+AND (IY-10)
 AND (IY+100)
+AND (IY-100)
 AND (IY+127)
+AND (IY-127)
 BIT 1, (HL)
 BIT 2, (HL)
 BIT 4, (HL)
 BIT 1, (IX)
 BIT 1, (IX+1)
+BIT 1, (IX-1)
 BIT 1, (IX+10)
+BIT 1, (IX-10)
 BIT 1, (IX+100)
+BIT 1, (IX-100)
 BIT 1, (IX+127)
+BIT 1, (IX-127)
 BIT 2, (IX)
 BIT 2, (IX+1)
+BIT 2, (IX-1)
 BIT 2, (IX+10)
+BIT 2, (IX-10)
 BIT 2, (IX+100)
+BIT 2, (IX-100)
 BIT 2, (IX+127)
+BIT 2, (IX-127)
 BIT 4, (IX)
 BIT 4, (IX+1)
+BIT 4, (IX-1)
 BIT 4, (IX+10)
+BIT 4, (IX-10)
 BIT 4, (IX+100)
+BIT 4, (IX-100)
 BIT 4, (IX+127)
+BIT 4, (IX-127)
 BIT 1, (IY)
 BIT 1, (IY+1)
+BIT 1, (IY-1)
 BIT 1, (IY+10)
+BIT 1, (IY-10)
 BIT 1, (IY+100)
+BIT 1, (IY-100)
 BIT 1, (IY+127)
+BIT 1, (IY-127)
 BIT 2, (IY)
 BIT 2, (IY+1)
+BIT 2, (IY-1)
 BIT 2, (IY+10)
+BIT 2, (IY-10)
 BIT 2, (IY+100)
+BIT 2, (IY-100)
 BIT 2, (IY+127)
+BIT 2, (IY-127)
 BIT 4, (IY)
 BIT 4, (IY+1)
+BIT 4, (IY-1)
 BIT 4, (IY+10)
+BIT 4, (IY-10)
 BIT 4, (IY+100)
+BIT 4, (IY-100)
 BIT 4, (IY+127)
+BIT 4, (IY-127)
 BIT 1, B
 BIT 1, C
 BIT 1, D
@@ -297,14 +337,22 @@ CP 64
 CP 128
 CP (IX)
 CP (IX+1)
+CP (IX-1)
 CP (IX+10)
+CP (IX-10)
 CP (IX+100)
+CP (IX-100)
 CP (IX+127)
+CP (IX-127)
 CP (IY)
 CP (IY+1)
+CP (IY-1)
 CP (IY+10)
+CP (IY-10)
 CP (IY+100)
+CP (IY-100)
 CP (IY+127)
+CP (IY-127)
 CPD
 CPDR
 CPI
@@ -315,15 +363,23 @@ DEC (HL)
 DEC IX
 DEC (IX)
 DEC (IX+1)
+DEC (IX-1)
 DEC (IX+10)
+DEC (IX-10)
 DEC (IX+100)
+DEC (IX-100)
 DEC (IX+127)
+DEC (IX-127)
 DEC IY
 DEC (IY)
 DEC (IY+1)
+DEC (IY-1)
 DEC (IY+10)
+DEC (IY-10)
 DEC (IY+100)
+DEC (IY-100)
 DEC (IY+127)
+DEC (IY-127)
 DEC B
 DEC C
 DEC D
@@ -380,15 +436,23 @@ INC (HL)
 INC IX
 INC (IX)
 INC (IX+1)
+INC (IX-1)
 INC (IX+10)
+INC (IX-10)
 INC (IX+100)
+INC (IX-100)
 INC (IX+127)
+INC (IX-127)
 INC IY
 INC (IY)
 INC (IY+1)
+INC (IY-1)
 INC (IY+10)
+INC (IY-10)
 INC (IY+100)
+INC (IY-100)
 INC (IY+127)
+INC (IY-127)
 INC B
 INC C
 INC D
@@ -1125,6 +1189,14 @@ LD (IX+1), 16
 LD (IX+1), 32
 LD (IX+1), 64
 LD (IX+1), 128
+LD (IX-1), 1
+LD (IX-1), 2
+LD (IX-1), 4
+LD (IX-1), 8
+LD (IX-1), 16
+LD (IX-1), 32
+LD (IX-1), 64
+LD (IX-1), 128
 LD (IX+10), 1
 LD (IX+10), 2
 LD (IX+10), 4
@@ -1133,6 +1205,14 @@ LD (IX+10), 16
 LD (IX+10), 32
 LD (IX+10), 64
 LD (IX+10), 128
+LD (IX-10), 1
+LD (IX-10), 2
+LD (IX-10), 4
+LD (IX-10), 8
+LD (IX-10), 16
+LD (IX-10), 32
+LD (IX-10), 64
+LD (IX-10), 128
 LD (IX+100), 1
 LD (IX+100), 2
 LD (IX+100), 4
@@ -1141,6 +1221,14 @@ LD (IX+100), 16
 LD (IX+100), 32
 LD (IX+100), 64
 LD (IX+100), 128
+LD (IX-100), 1
+LD (IX-100), 2
+LD (IX-100), 4
+LD (IX-100), 8
+LD (IX-100), 16
+LD (IX-100), 32
+LD (IX-100), 64
+LD (IX-100), 128
 LD (IX+127), 1
 LD (IX+127), 2
 LD (IX+127), 4
@@ -1149,6 +1237,14 @@ LD (IX+127), 16
 LD (IX+127), 32
 LD (IX+127), 64
 LD (IX+127), 128
+LD (IX-127), 1
+LD (IX-127), 2
+LD (IX-127), 4
+LD (IX-127), 8
+LD (IX-127), 16
+LD (IX-127), 32
+LD (IX-127), 64
+LD (IX-127), 128
 LD (IY), 1
 LD (IY), 2
 LD (IY), 4
@@ -1165,6 +1261,14 @@ LD (IY+1), 16
 LD (IY+1), 32
 LD (IY+1), 64
 LD (IY+1), 128
+LD (IY-1), 1
+LD (IY-1), 2
+LD (IY-1), 4
+LD (IY-1), 8
+LD (IY-1), 16
+LD (IY-1), 32
+LD (IY-1), 64
+LD (IY-1), 128
 LD (IY+10), 1
 LD (IY+10), 2
 LD (IY+10), 4
@@ -1173,6 +1277,14 @@ LD (IY+10), 16
 LD (IY+10), 32
 LD (IY+10), 64
 LD (IY+10), 128
+LD (IY-10), 1
+LD (IY-10), 2
+LD (IY-10), 4
+LD (IY-10), 8
+LD (IY-10), 16
+LD (IY-10), 32
+LD (IY-10), 64
+LD (IY-10), 128
 LD (IY+100), 1
 LD (IY+100), 2
 LD (IY+100), 4
@@ -1181,6 +1293,14 @@ LD (IY+100), 16
 LD (IY+100), 32
 LD (IY+100), 64
 LD (IY+100), 128
+LD (IY-100), 1
+LD (IY-100), 2
+LD (IY-100), 4
+LD (IY-100), 8
+LD (IY-100), 16
+LD (IY-100), 32
+LD (IY-100), 64
+LD (IY-100), 128
 LD (IY+127), 1
 LD (IY+127), 2
 LD (IY+127), 4
@@ -1189,6 +1309,14 @@ LD (IY+127), 16
 LD (IY+127), 32
 LD (IY+127), 64
 LD (IY+127), 128
+LD (IY-127), 1
+LD (IY-127), 2
+LD (IY-127), 4
+LD (IY-127), 8
+LD (IY-127), 16
+LD (IY-127), 32
+LD (IY-127), 64
+LD (IY-127), 128
 LD (IX), B
 LD (IX), C
 LD (IX), D
@@ -1203,6 +1331,13 @@ LD (IX+1), E
 LD (IX+1), H
 LD (IX+1), L
 LD (IX+1), A
+LD (IX-1), B
+LD (IX-1), C
+LD (IX-1), D
+LD (IX-1), E
+LD (IX-1), H
+LD (IX-1), L
+LD (IX-1), A
 LD (IX+10), B
 LD (IX+10), C
 LD (IX+10), D
@@ -1210,6 +1345,13 @@ LD (IX+10), E
 LD (IX+10), H
 LD (IX+10), L
 LD (IX+10), A
+LD (IX-10), B
+LD (IX-10), C
+LD (IX-10), D
+LD (IX-10), E
+LD (IX-10), H
+LD (IX-10), L
+LD (IX-10), A
 LD (IX+100), B
 LD (IX+100), C
 LD (IX+100), D
@@ -1217,6 +1359,13 @@ LD (IX+100), E
 LD (IX+100), H
 LD (IX+100), L
 LD (IX+100), A
+LD (IX-100), B
+LD (IX-100), C
+LD (IX-100), D
+LD (IX-100), E
+LD (IX-100), H
+LD (IX-100), L
+LD (IX-100), A
 LD (IX+127), B
 LD (IX+127), C
 LD (IX+127), D
@@ -1224,6 +1373,13 @@ LD (IX+127), E
 LD (IX+127), H
 LD (IX+127), L
 LD (IX+127), A
+LD (IX-127), B
+LD (IX-127), C
+LD (IX-127), D
+LD (IX-127), E
+LD (IX-127), H
+LD (IX-127), L
+LD (IX-127), A
 LD (IY), B
 LD (IY), C
 LD (IY), D
@@ -1238,6 +1394,13 @@ LD (IY+1), E
 LD (IY+1), H
 LD (IY+1), L
 LD (IY+1), A
+LD (IY-1), B
+LD (IY-1), C
+LD (IY-1), D
+LD (IY-1), E
+LD (IY-1), H
+LD (IY-1), L
+LD (IY-1), A
 LD (IY+10), B
 LD (IY+10), C
 LD (IY+10), D
@@ -1245,6 +1408,13 @@ LD (IY+10), E
 LD (IY+10), H
 LD (IY+10), L
 LD (IY+10), A
+LD (IY-10), B
+LD (IY-10), C
+LD (IY-10), D
+LD (IY-10), E
+LD (IY-10), H
+LD (IY-10), L
+LD (IY-10), A
 LD (IY+100), B
 LD (IY+100), C
 LD (IY+100), D
@@ -1252,6 +1422,13 @@ LD (IY+100), E
 LD (IY+100), H
 LD (IY+100), L
 LD (IY+100), A
+LD (IY-100), B
+LD (IY-100), C
+LD (IY-100), D
+LD (IY-100), E
+LD (IY-100), H
+LD (IY-100), L
+LD (IY-100), A
 LD (IY+127), B
 LD (IY+127), C
 LD (IY+127), D
@@ -1259,76 +1436,139 @@ LD (IY+127), E
 LD (IY+127), H
 LD (IY+127), L
 LD (IY+127), A
+LD (IY-127), B
+LD (IY-127), C
+LD (IY-127), D
+LD (IY-127), E
+LD (IY-127), H
+LD (IY-127), L
+LD (IY-127), A
 LD B, (IX)
 LD B, (IX+1)
+LD B, (IX-1)
 LD B, (IX+10)
+LD B, (IX-10)
 LD B, (IX+100)
+LD B, (IX-100)
 LD B, (IX+127)
+LD B, (IX-127)
 LD C, (IX)
 LD C, (IX+1)
+LD C, (IX-1)
 LD C, (IX+10)
+LD C, (IX-10)
 LD C, (IX+100)
+LD C, (IX-100)
 LD C, (IX+127)
+LD C, (IX-127)
 LD D, (IX)
 LD D, (IX+1)
+LD D, (IX-1)
 LD D, (IX+10)
+LD D, (IX-10)
 LD D, (IX+100)
+LD D, (IX-100)
 LD D, (IX+127)
+LD D, (IX-127)
 LD E, (IX)
 LD E, (IX+1)
+LD E, (IX-1)
 LD E, (IX+10)
+LD E, (IX-10)
 LD E, (IX+100)
+LD E, (IX-100)
 LD E, (IX+127)
+LD E, (IX-127)
 LD H, (IX)
 LD H, (IX+1)
+LD H, (IX-1)
 LD H, (IX+10)
+LD H, (IX-10)
 LD H, (IX+100)
+LD H, (IX-100)
 LD H, (IX+127)
+LD H, (IX-127)
 LD L, (IX)
 LD L, (IX+1)
+LD L, (IX-1)
 LD L, (IX+10)
+LD L, (IX-10)
 LD L, (IX+100)
+LD L, (IX-100)
 LD L, (IX+127)
+LD L, (IX-127)
 LD A, (IX)
 LD A, (IX+1)
+LD A, (IX-1)
 LD A, (IX+10)
+LD A, (IX-10)
 LD A, (IX+100)
+LD A, (IX-100)
 LD A, (IX+127)
+LD A, (IX-127)
 LD B, (IY)
 LD B, (IY+1)
+LD B, (IY-1)
 LD B, (IY+10)
+LD B, (IY-10)
 LD B, (IY+100)
+LD B, (IY-100)
 LD B, (IY+127)
+LD B, (IY-127)
 LD C, (IY)
 LD C, (IY+1)
+LD C, (IY-1)
 LD C, (IY+10)
+LD C, (IY-10)
 LD C, (IY+100)
+LD C, (IY-100)
 LD C, (IY+127)
+LD C, (IY-127)
 LD D, (IY)
 LD D, (IY+1)
+LD D, (IY-1)
 LD D, (IY+10)
+LD D, (IY-10)
 LD D, (IY+100)
+LD D, (IY-100)
 LD D, (IY+127)
+LD D, (IY-127)
 LD E, (IY)
 LD E, (IY+1)
+LD E, (IY-1)
 LD E, (IY+10)
+LD E, (IY-10)
 LD E, (IY+100)
+LD E, (IY-100)
 LD E, (IY+127)
+LD E, (IY-127)
 LD H, (IY)
 LD H, (IY+1)
+LD H, (IY-1)
 LD H, (IY+10)
+LD H, (IY-10)
 LD H, (IY+100)
+LD H, (IY-100)
 LD H, (IY+127)
+LD H, (IY-127)
 LD L, (IY)
 LD L, (IY+1)
+LD L, (IY-1)
 LD L, (IY+10)
+LD L, (IY-10)
 LD L, (IY+100)
+LD L, (IY-100)
 LD L, (IY+127)
+LD L, (IY-127)
 LD A, (IY)
 LD A, (IY+1)
+LD A, (IY-1)
 LD A, (IY+10)
+LD A, (IY-10)
 LD A, (IY+100)
+LD A, (IY-100)
 LD A, (IY+127)
+LD A, (IY-127)
 LDD
 LDDR
 LDI
@@ -1353,14 +1593,22 @@ OR 64
 OR 128
 OR (IX)
 OR (IX+1)
+OR (IX-1)
 OR (IX+10)
+OR (IX-10)
 OR (IX+100)
+OR (IX-100)
 OR (IX+127)
+OR (IX-127)
 OR (IY)
 OR (IY+1)
+OR (IY-1)
 OR (IY+10)
+OR (IY-10)
 OR (IY+100)
+OR (IY-100)
 OR (IY+127)
+OR (IY-127)
 OTDR
 OTIR
 OUT (1), A
@@ -1395,34 +1643,58 @@ RES 2, (HL)
 RES 4, (HL)
 RES 1, (IX)
 RES 1, (IX+1)
+RES 1, (IX-1)
 RES 1, (IX+10)
+RES 1, (IX-10)
 RES 1, (IX+100)
+RES 1, (IX-100)
 RES 1, (IX+127)
+RES 1, (IX-127)
 RES 2, (IX)
 RES 2, (IX+1)
+RES 2, (IX-1)
 RES 2, (IX+10)
+RES 2, (IX-10)
 RES 2, (IX+100)
+RES 2, (IX-100)
 RES 2, (IX+127)
+RES 2, (IX-127)
 RES 4, (IX)
 RES 4, (IX+1)
+RES 4, (IX-1)
 RES 4, (IX+10)
+RES 4, (IX-10)
 RES 4, (IX+100)
+RES 4, (IX-100)
 RES 4, (IX+127)
+RES 4, (IX-127)
 RES 1, (IY)
 RES 1, (IY+1)
+RES 1, (IY-1)
 RES 1, (IY+10)
+RES 1, (IY-10)
 RES 1, (IY+100)
+RES 1, (IY-100)
 RES 1, (IY+127)
+RES 1, (IY-127)
 RES 2, (IY)
 RES 2, (IY+1)
+RES 2, (IY-1)
 RES 2, (IY+10)
+RES 2, (IY-10)
 RES 2, (IY+100)
+RES 2, (IY-100)
 RES 2, (IY+127)
+RES 2, (IY-127)
 RES 4, (IY)
 RES 4, (IY+1)
+RES 4, (IY-1)
 RES 4, (IY+10)
+RES 4, (IY-10)
 RES 4, (IY+100)
+RES 4, (IY-100)
 RES 4, (IY+127)
+RES 4, (IY-127)
 RES 1, B
 RES 1, C
 RES 1, D
@@ -1505,34 +1777,58 @@ SET 2, (HL)
 SET 4, (HL)
 SET 1, (IX)
 SET 1, (IX+1)
+SET 1, (IX-1)
 SET 1, (IX+10)
+SET 1, (IX-10)
 SET 1, (IX+100)
+SET 1, (IX-100)
 SET 1, (IX+127)
+SET 1, (IX-127)
 SET 2, (IX)
 SET 2, (IX+1)
+SET 2, (IX-1)
 SET 2, (IX+10)
+SET 2, (IX-10)
 SET 2, (IX+100)
+SET 2, (IX-100)
 SET 2, (IX+127)
+SET 2, (IX-127)
 SET 4, (IX)
 SET 4, (IX+1)
+SET 4, (IX-1)
 SET 4, (IX+10)
+SET 4, (IX-10)
 SET 4, (IX+100)
+SET 4, (IX-100)
 SET 4, (IX+127)
+SET 4, (IX-127)
 SET 1, (IY)
 SET 1, (IY+1)
+SET 1, (IY-1)
 SET 1, (IY+10)
+SET 1, (IY-10)
 SET 1, (IY+100)
+SET 1, (IY-100)
 SET 1, (IY+127)
+SET 1, (IY-127)
 SET 2, (IY)
 SET 2, (IY+1)
+SET 2, (IY-1)
 SET 2, (IY+10)
+SET 2, (IY-10)
 SET 2, (IY+100)
+SET 2, (IY-100)
 SET 2, (IY+127)
+SET 2, (IY-127)
 SET 4, (IY)
 SET 4, (IY+1)
+SET 4, (IY-1)
 SET 4, (IY+10)
+SET 4, (IY-10)
 SET 4, (IY+100)
+SET 4, (IY-100)
 SET 4, (IY+127)
+SET 4, (IY-127)
 SET 1, B
 SET 1, C
 SET 1, D

tools/tests/zasm/geninstrs.py

@@ -103,7 +103,7 @@ def genargs(argspec):
         argspec = argspec.upper()
         for n in [1, 10, 100, 127]:
             result.append(f"(I{argspec}+{n})")
-        # TODO: support minus
+            result.append(f"(I{argspec}-{n})")
         return result
     if argspec in argspecTbl:
         return [argspecTbl[argspec]]

tools/tests/zasm/test1.asm

@@ -17,7 +17,7 @@ label2: .dw	0x42
 	ld	ix, 1234
 	ld	iy, 2345
 	ld	(ix+1), l
-	ld	l, (ix+1)
+	ld	l, (ix-1)
 	ld	hl, 0x100
 .equ	baz	0x20
 	; accept space before comma