8086asm: add support for modrm 8-bit displacement

find is the biggest chunk of logic of the boot code. The 8086 version
is significantly terser than the z80 one. REP/CMPS helps...

blk/730

@@ -6,7 +6,7 @@ Mnemonics are followed by argument types. For example, MOVri,
 moves 8-bit immediate to 8-bit register.
 
 'r' = 8-bit register           'x' = 16-bit register
-'i' = immediate, size depends on other operand.
+'i' = 8-bit immediate          'I' = 16-bit immediate
 's' = SREG register
 
 Mnemonics that only have one signature (for example INT,) don't

blk/755

@@ -1,11 +1,16 @@
 : OPrm CREATE C, DOES> C@ A, SWAP 3 LSHIFT OR A, ;
 0x8a OPrm MOVr[],    0x8b OPrm MOVx[],
 
+: OPrm+ ( r m off ) CREATE C, DOES>
+    C@ A, ROT 3 LSHIFT ROT OR 0x40 OR A, A, ;
+0x8a OPrm+ MOVr[]+,    0x8b OPrm+ MOVx[]+,
+
 : MOVri, SWAP 0xb0 OR A, A, ;
-: MOVxi, SWAP 0xb8 OR A, A,, ;
+: MOVxI, SWAP 0xb8 OR A, A,, ;
 : MOVsx, 0x8e A, SWAP 3 LSHIFT OR 0xc0 OR A, ;
 : MOVxm, 0x8b A, SWAP 3 LSHIFT 0x6 OR A, A,, ;
 : INT, 0xcd A, A, ;
-: ADDAXi, 0x05 A, A,, ; : ADDALi, 0x04 A, A, ;
+: ADDAXI, 0x05 A, A,, ; : ADDALi, 0x04 A, A, ;
+: SUBxi, 0x83 A, SWAP 0xe8 OR A, A, ;
 : JMPr, 0xff A, 7 AND 0xe0 OR A, ;
 : JMPf, ( seg off ) 0xea A, SPLITB A, A, A,, ;

blk/811

@@ -2,9 +2,9 @@ H@ ORG ! 0x7c00 BIN( ! ( BIOS loads boot bin at 0x7c00 )
 JMPs, L1 FWRs ( start )
 ORG @ 0x25 + HERE ! ( bypass BPB )
 L1 FSET ( start )
-CLI, CLD, AX 0x800 MOVxi, DS AX MOVsx, ES AX MOVsx,
+CLI, CLD, AX 0x800 MOVxI, DS AX MOVsx, ES AX MOVsx,
-SS AX MOVsx, SP 0xffff MOVxi, STI,
+SS AX MOVsx, SP 0xffff MOVxI, STI,
-AH 2 MOVri, DX 0 MOVxi, CH 0 MOVri, CL 2 MOVri, AL 1 MOVri,
+AH 2 MOVri, DX 0 MOVxI, CH 0 MOVri, CL 2 MOVri, AL 1 MOVri,
-BX 0 MOVxi, 0x13 INT, ( read 2nd sector of boot floppy )
+BX 0 MOVxI, 0x13 INT, ( read 2nd sector of boot floppy )
 0x800 0 JMPf,
 ORG @ 0x1fe + HERE ! 0x55 A, 0xaa A,

blk/812

@@ -5,7 +5,7 @@ JMPn, 0 A,,   ( 00, main )     JMPn, 0 A,,   ( 03, find )
 0 A,          ( 0a, unused )   JMPn, 0 A,,   ( 0b, cellWord )
 JMPn, 0 A,, ( 0e compiledWord ) JMPn, 0 A,,  ( 11, pushRS )
 JMPn, 0 A,,   ( 14, popRS )
-BX JMPr,      ( 17, nativeWord ) 0 A,
+DI JMPr,      ( 17, nativeWord ) 0 A,
 JMPn, 0 A,,   ( 1a, next )     JMPn, 0 A,,   ( 1d, unused )
 0 A, 0 A,     ( 20, numberWord ) 0 A, 0 A,   ( 22, litWord )
 0 A, 0 A,     ( 24, addrWord ) 0 A, 0 A,     ( 26, unused )

blk/813

@@ -9,5 +9,5 @@ H@ XCURRENT !        ( set current tip of dict, 0x42 )
 ;CODE
 CODE FOO
     AH 0x0e MOVri, ( print char ) AL 'X' MOVri, 0x10 INT,
-    L2 BSET JMPs, L2 @ RPCs,
+    BEGIN, JMPs, AGAIN,
 ;CODE

blk/814

@@ -1,5 +1,5 @@
-L1 BSET PC 3 - ORG @ 0x34 + ! ( execute -- BX -> wordref )
+L1 BSET PC 3 - ORG @ 0x34 + ! ( execute -- DI -> wordref )
     AH AH XORrr,
-    AL [BX] MOVr[],
+    AL [DI] MOVr[],
-    BX INCx, ( PFA )
+    DI INCx, ( PFA )
     AX JMPr,

blk/815

@@ -1,14 +1,16 @@
 L4 BSET PC 3 - ORG @ 4 + ! ( find )
 ( find word the same name as str in SI starting from tip in
-  BX. Returns wordref in BX. Z if found, NZ if not. )
+  DI. Returns wordref in BX. Z if found, NZ if not. )
     CH CH XORrr, CL [SI] MOVr[], ( CX -> strlen )
-    SI INCx,
+    SI INCx, ( first char ) AX AX XORxx, ( initial prev )
-    AX AX XORxx, ( initial prev )
+    BEGIN, ( loop )
-    BEGIN, ( inner )
+        DI AX SUBxx, ( jump to prev wordref )
-        BX AX SUBxx, ( jump to prev wordref )
+        AL [DI] -1 MOVr[]+, ( strlen )
-        BX DECx, AL [BX] MOVr[], ( strlen )
+        CL AL CMPrr, IFZ, ( same len )
-        CL AL CMPrr, IFZ, BX INCx, RETn, THEN,
+            SI PUSHx, DI PUSHx, CX PUSHx, ( --> lvl 3 )
-        BX DECx, BX DECx, AX [BX] MOVx[], ( prev )
+            3 ADDALi, ( header ) AH AH XORrr, DI AX SUBxx,
-        AX AX ORxx,
+            REPZ, CMPSB,
-    JNZ, AGAIN,
+            CX POPx, DI POPx, SI POPx, ( <-- lvl 3 )
-    BEGIN, JMPs, AGAIN,
+            IFZ, AL AL XORrr, ( Z ) RETn, THEN,
+        THEN,
+                                                      ( cont. )

blk/816

@@ -1,6 +1,6 @@
-L3 BSET 3 A, 'F' A, 'O' A, 'O' A,
+( find cont. )
-PC 3 - ORG @ 1+ ! ( main )
+        DI 3 SUBxi, AX [DI] MOVx[], ( prev )
-    BX 0x08 MOVxm, ( LATEST )
+        AX AX ORxx,
-    SI L3 @ MOVxi,
+    JNZ, AGAIN, ( loop )
-    CALLn, L4 @ RPCn, ( find )
+    AX INCx, ( NZ ) RETn,
-    JMPs, L1 @ RPCs, ( execute )
+

blk/817

@@ -0,0 +1,8 @@
+L3 BSET 3 A, 'F' A, 'O' A, 'O' A,
+PC 3 - ORG @ 1+ ! ( main )
+    DI 0x08 MOVxm, ( LATEST )
+    SI L3 @ MOVxI,
+    CALLn, L4 @ RPCn, ( find )
+    IFZ, JMPs, L1 @ RPCs, ( execute ) THEN,
+    AH 0x0e MOVri, ( print char ) AL '!' MOVri, 0x10 INT,
+    BEGIN, JMPs, AGAIN,

recipes/pcat/xcomp.fs

@@ -1,7 +1,7 @@
 750 LOAD  ( 8086 asm )
 262 LOAD  ( xcomp )
 270 LOAD  ( xcomp overrides )
-812 816 LOADR
+812 817 LOADR
 (entry) _
 ( Update LATEST )
 PC ORG @ 8 + !