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avra: add branching instructions
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@ -8,8 +8,32 @@
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; categories, and then alphabetically. Categories are ordered so that the 8bit
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; opcodes come first, then the 16bit ones. 0xff ends the chain
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instrNames:
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; Branching instructions. They are all shortcuts to BRBC/BRBS. Their respective
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; bits are listed in instrBRBits. These are not in alphabetical order, but
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; rather in "bit order". All "bit set" instructions first (10th bit clear), then
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; all "bit clear" ones (10th bit set). Inside this order, they're then in "sss"
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; order (bit number alias for BRBC/BRBS)
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.db "BRCS", 0
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.db "BREQ", 0
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.db "BRMI", 0
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.db "BRVS", 0
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.db "BRLT", 0
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.db "BRHS", 0
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.db "BRTS", 0
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.db "BRIE", 0
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.db "BRCC", 0
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.db "BRNE", 0
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.db "BRPL", 0
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.db "BRVC", 0
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.db "BRGE", 0
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.db "BRHC", 0
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.db "BRTC", 0
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.db "BRID", 0
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.equ I_BRBS 16
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.db "BRBS", 0
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.db "BRBC", 0
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; Rd(5) + Rr(5)
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.equ I_ADC 0
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.equ I_ADC 18
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.db "ADC", 0
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.db "ADD", 0
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.db "AND", 0
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@ -24,7 +48,7 @@ instrNames:
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.db "SBC", 0
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.db "SUB", 0
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; no arg
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.equ I_BREAK 13
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.equ I_BREAK 31
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.db "BREAK", 0
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.db "CLC", 0
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.db "CLH", 0
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@ -52,7 +76,7 @@ instrNames:
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.db "SLEEP", 0
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.db "WDR", 0
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; Rd(5)
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.equ I_ASR 39
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.equ I_ASR 57
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.db "ASR", 0
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.db "COM", 0
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.db "DEC", 0
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@ -134,6 +158,25 @@ instrUpMasks2:
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.db 0b10010100, 0b00000010 ; SWAP
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.db 0b10010010, 0b00000100 ; XCH
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instrBRBits:
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; 1st bit is 3rd bit of MSB and the other 3 are the lower bits of LSB
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.db 0b0000 ; BRCS
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.db 0b0001 ; BREQ
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.db 0b0010 ; BRMI
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.db 0b0011 ; BRVS
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.db 0b0100 ; BRLT
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.db 0b0101 ; BRHS
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.db 0b0110 ; BRTS
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.db 0b0111 ; BRIE
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.db 0b1000 ; BRCC
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.db 0b1001 ; BRNE
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.db 0b1010 ; BRPL
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.db 0b1011 ; BRVC
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.db 0b1100 ; BRGE
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.db 0b1101 ; BRHC
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.db 0b1110 ; BRTC
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.db 0b1111 ; BRID
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; Same signature as getInstID in instr.asm
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; Reads string in (HL) and returns the corresponding ID (I_*) in A. Sets Z if
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; there's a match.
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@ -172,6 +215,8 @@ getInstID:
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parseInstruction:
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; BC, during .spit, is ORred to the spitted opcode.
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ld bc, 0
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cp I_ADC
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jp c, .BR
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cp I_BREAK
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jr c, .spitRd5Rr5
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cp I_ASR
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@ -207,8 +252,7 @@ parseInstruction:
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or b
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ld b, a
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ld a, d ; restore A
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ld hl, instrUpMasks1
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call addHL
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call .getUp1
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; now that's our MSB
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jr .spitMSB
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.spit:
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@ -225,6 +269,77 @@ parseInstruction:
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xor a ; ensure Z, set success
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ret
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; Spit a branching mnemonic.
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.BR:
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; While we have our index in A, let's settle B straight: Our base
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; upcode is 0b11110000 for "bit set" types and 0b11110100 for "bit
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; clear" types. However, we'll have 2 left shift operation done on B
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; later on, so we need those bits shifted right.
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ld b, 0b111100
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cp I_BRBS
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jr z, .rdBRBS
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jr nc, .rdBRBC
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; We have an alias. Our "sss" value is index & 0b111
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; Before we get rid of that 3rd bit, let's see, is it set? if yes, we'll
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; want to increase B
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bit 3, a
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jr z, .skip1 ; 3rd bit unset
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inc b
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.skip1:
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and 0b111
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ld c, a
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.spitBR2:
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call readWord
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ret nz
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call parseExpr
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ret nz
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; IX contains an absolute value. Turn this into a -64/+63 relative
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; value by subtracting PC from it. However, before we do that, let's
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; add 0x7f to it, which we'll remove later. This will simplify bounds
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; checks. (we use 7f instead of 3f because we deal in bytes here, not
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; in words)
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push ix \ pop hl
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ld de, 0x7f
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add hl, de ; Carry cleared
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ex de, hl
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call zasmGetPC ; --> HL
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; The relative value is actually not relative to current PC, but to
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; PC after the execution of this branching op. Increase HL by 2.
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inc hl \ inc hl
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ex de, hl
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sbc hl, de
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jp c, unsetZ ; Carry? error
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ld de, 0x7f
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sbc hl, de
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; We're within bounds! However, our value in L is the number of
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; relative *bytes*. The value we put there is the number of words.
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; Thefore, relevant bits are 7:1
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ld a, l
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sla a \ rl b
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sla a \ rl b
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; k is now shifted by 3, two of those bits being in B. Let's OR A and
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; C and we have our LSB ready to go.
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or c
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call ioPutB
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; Good! MSB now. B is already good to go.
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ld a, b
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jp ioPutB
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.rdBRBC:
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; In addition to reading "sss", we also need to inc B so that our base
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; upcode becomes 0b111101
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inc b
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.rdBRBS:
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call readWord
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ret nz
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call parseExpr
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ld a, 7
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call .IX2A
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ret nz
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ld c, a
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call readComma
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ret nz
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jr .spitBR2
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; local routines
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; place number in A in BC at position .......d dddd....
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; BC is assumed to be 0
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@ -233,6 +348,13 @@ parseInstruction:
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rl b
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ld c, a
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ret
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; Fetch a 8-bit upcode specified by instr index in A and set that upcode in HL
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.getUp1:
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sub I_ADC
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ld hl, instrUpMasks1
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jp addHL
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; Fetch a 16-bit upcode specified by instr index in A and set that upcode in HL
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.getUp2:
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sub I_BREAK
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@ -251,13 +373,19 @@ parseInstruction:
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inc hl
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call parseDecimal
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ret nz
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ld a, 31
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jr .IX2A
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; Put IX's LSB into A and, additionally, ensure that the new value is <=
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; than what was previously in A.
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; Z for success.
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.IX2A:
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push ix \ pop hl
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cp l
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jp c, unsetZ ; A < L
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ld a, h
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or a
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ret nz ; should be zero
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ld a, l
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cp 32
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jp nc, unsetZ ; must be < 32
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; we're good!
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cp a ; ensure Z
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; Z set from "or a"
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ret
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@ -1,5 +1,9 @@
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add r1, r31
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ret
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foo:
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sleep
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break
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breq bar
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asr r20
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bar:
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brbs 6, foo
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@ -1 +1 @@
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•ˆ•˜•E•
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <09>E<EFBFBD><45><EFBFBD>
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@ -51,6 +51,12 @@ test:
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jp nz, fail
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call nexttest
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; test that AND affects the Z flag
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ld a, 0x69
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and 0x80
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jp nz, fail
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call nexttest
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; success
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xor a
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halt
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