forth: add label system to z80 assembler
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Virgil Dupras
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@ -5,8 +5,58 @@
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256 /MOD SWAP
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;
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( A, spits an assembled byte, A,, spits an assembled word )
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( To debug, change C, to .X )
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: A, C, ;
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: A,, SPLITB A, A, ;
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( Labels are a convenient way of managing relative jump
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calculations. Backward labels are easy. It is only a matter
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or recording "HERE" and do subtractions. Forward labels
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record the place where we should write the offset, and then
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when we get to that point later on, the label records the
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offset there.
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To avoid using dict memory in compilation targets, we
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pre-declare label variables here, which means we have a
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limited number of it. For now, 4 ought to be enough. )
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(sysv) L1
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(sysv) L2
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(sysv) L3
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(sysv) L4
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( There are 2 label types: backward and forward. For each
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type, there are two actions: set and write. Setting a label
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is declaring where it is. It has to be performed at the
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label's destination. Writing a label is writing its offset
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difference to the binary result. It has to be done right
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after a relative jump operation. Yes, labels are only for
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relative jumps.
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For backward labels, set happens before write. For forward
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labels, write happen before set. The write operation writes
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a dummy placeholder, and then the set operation writes the
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offset at that placeholder's address.
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Variable actions are expected to be called with labels in
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front of them. Example, "L2 FSET"
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About that "1 -": z80 relative jumps record "e-2", that is,
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the offset that *counts the 2 bytes of the jump itself*.
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Because we set the label *after* the jump OP1 itself, that's
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1 byte that is taken care of. We still need to adjust by
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another byte before writing the offset.
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)
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: BSET H@ SWAP ! ;
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: BWR @ H@ - 1 - A, ;
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( same as BSET, but we need to write a placeholder )
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: FWR BSET 0 A, ;
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: FSET @ DUP H@ -^ 1 - SWAP C! ;
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( "r" register constants )
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7 CONSTANT A
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0 CONSTANT B
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1 CONSTANT C
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@ -15,6 +65,8 @@
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4 CONSTANT H
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5 CONSTANT L
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6 CONSTANT (HL)
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( "ss" register constants )
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0 CONSTANT BC
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1 CONSTANT DE
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2 CONSTANT HL
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@ -38,6 +90,7 @@
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( -- )
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: OP1 CREATE C, DOES> C@ A, ;
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0xeb OP1 EXDEHL,
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0xd9 OP1 EXX,
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0x76 OP1 HALT,
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0xe9 OP1 JP(HL),
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0x12 OP1 LD(DE)A,
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@ -49,6 +102,19 @@
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0x0f OP1 RRCA,
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0x37 OP1 SCF,
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( Relative jumps are a bit special. They're supposed to take
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an argument, but they don't take it so they can work with
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the label system. Therefore, relative jumps are an OP1 but
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when you use them, you're expected to write the offset
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afterwards yourself. )
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0x18 OP1 JR,
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0x38 OP1 JRC,
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0x30 OP1 JRNC,
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0x28 OP1 JRZ,
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0x20 OP1 JRNZ,
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0x10 OP1 DJNZ,
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( r -- )
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: OP1r
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CREATE C,
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@ -72,6 +138,7 @@
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0xb0 OP1r0 ORr,
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0xa8 OP1r0 XORr,
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0xb8 OP1r0 CPr,
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0x90 OP1r0 SUBr
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( qq -- also works for ss )
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: OP1qq
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@ -200,7 +267,7 @@
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ROT ( nn op dd )
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<<4 ( nn op dd<<4 )
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OR A,
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SPLITB A, A,
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A,,
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;
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0x01 OP3ddnn LDddnn,
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@ -209,39 +276,27 @@
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CREATE C,
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DOES>
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C@ A,
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SPLITB A, A,
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A,,
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;
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0xcd OP3nn CALLnn,
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0xc3 OP3nn JPnn,
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0x22 OP3nn LD(nn)HL,
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0x2a OP3nn LDHL(nn),
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: OPJR
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CREATE C,
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DOES>
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C@ A, 2 - A,
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;
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0x18 OPJR JRe,
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0x38 OPJR JRCe,
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0x30 OPJR JRNCe,
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0x28 OPJR JRZe,
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0x20 OPJR JRNZe,
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0x10 OPJR DJNZe,
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( Specials )
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( dd nn -- )
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: LDdd(nn),
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0xed A,
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SWAP <<4 0x4b OR A,
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SPLITB A, A,
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A,,
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;
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( nn dd -- )
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: LD(nn)dd,
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0xed A,
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<<4 0x43 OR A,
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SPLITB A, A,
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A,,
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;
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( 26 == next )
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@ -155,10 +155,10 @@ CODE NOT
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A L LDrr,
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H ORr,
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HL 0 LDddnn,
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3 JRNZe, ( skip)
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JRNZ, L1 FWR ( skip )
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( false, make 1 )
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HL INCss,
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( skip )
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L1 FSET ( skip )
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HL PUSHqq,
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;CODE
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@ -190,13 +190,13 @@ CODE *
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HL ADDHLss,
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E RLr,
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D RLr,
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6 JRNCe, ( noinc )
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JRNC, 4 A, ( noinc )
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BC ADDHLss,
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3 JRNCe, ( noinc )
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JRNC, 1 A, ( noinc )
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DE INCss,
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( noinc )
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A DECr,
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-12 JRNZe, ( loop )
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JRNZ, -14 A, ( loop )
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HL PUSHqq,
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;CODE
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@ -210,17 +210,17 @@ CODE /MOD
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A B LDrr,
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B 16 LDrn,
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HL 0 LDddnn,
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( loop )
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L1 BSET ( loop )
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SCF,
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C RLr,
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RLA,
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HL ADCHLss,
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DE SBCHLss,
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4 JRNCe, ( skip )
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JRNC, L2 FWR ( skip )
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DE ADDHLss,
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C DECr,
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( skip )
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-12 DJNZe, ( loop )
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L2 FSET ( skip )
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DJNZ, L1 BWR ( loop )
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B A LDrr,
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HL PUSHqq,
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BC PUSHqq,
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@ -318,9 +318,9 @@ CODE IMMED?
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HL DECss,
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DE 0 LDddnn,
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7 (HL) BITbr,
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3 JRZe, ( notset )
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JRZ, L1 FWR ( notset )
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DE INCss,
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( notset )
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L1 FSET ( notset )
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DE PUSHqq,
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;CODE
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@ -342,15 +342,16 @@ CODE SCMP
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DE POPqq,
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HL POPqq,
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chkPS,
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( loop )
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L1 BSET ( loop )
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LDA(DE),
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(HL) CPr,
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7 JRNZe, ( not equal? break early to "end". NZ is set. )
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JRNZ, L2 FWR ( not equal? break early to "end".
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NZ is set. )
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A ORr, ( if our char is null, stop )
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HL INCss,
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DE INCss,
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-7 JRNZe, ( loop )
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( end )
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JRNZ, L1 BWR ( loop )
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L2 FSET ( end )
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( 40 == flagsToBC )
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40 CALLnn,
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BC PUSHqq,
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@ -372,13 +373,13 @@ CODE (parsed)
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chkPS,
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( 60 == parseDecimal )
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60 CALLnn,
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10 JRZe, ( success )
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JRZ, L1 FWR ( success )
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( error )
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DE 0 LDddnn,
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DE PUSHqq, ( dummy )
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DE PUSHqq, ( flag )
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JPNEXT,
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( success )
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L1 FSET ( success )
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DE PUSHqq,
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DE 1 LDddnn,
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DE PUSHqq,
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@ -389,13 +390,13 @@ CODE (find)
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chkPS,
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( 3 == find )
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3 CALLnn,
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10 JRZe, ( found )
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JRZ, L1 FWR ( found )
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( not found )
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HL PUSHqq,
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DE 0 LDddnn,
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DE PUSHqq,
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JPNEXT,
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( found )
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L1 FSET ( found )
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DE PUSHqq,
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DE 1 LDddnn,
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DE PUSHqq,
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@ -406,14 +407,14 @@ CODE SCPY
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chkPS,
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DE HERE LDdd(nn),
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B 0 LDrn,
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( loop )
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L1 BSET ( loop )
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A (HL) LDrr,
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LD(DE)A,
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HL INCss,
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DE INCss,
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B INCr,
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A ORr,
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-6 JRNZe, ( loop )
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JRNZ, L1 BWR ( loop )
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DE A LD(dd)r
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HERE DE LD(nn)dd,
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;CODE
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