duskos

commit 3bf9b0863d0c8f1519e9c17b1601b412371818be
parent d4f34dd6c76b4aafa0d8bad55fa309f61f2407e1
Author: Virgil Dupras <hsoft@hardcoded.net>
Date:   Thu,  9 Jun 2022 15:41:08 -0400

asm: simplify messed up modrm2, word

Diffstat:
M
fs/asm.fs
 | 
25
+++++++++++++------------

1 file changed, 13 insertions(+), 12 deletions(-)
diff --git a/fs/asm.fs b/fs/asm.fs
@@ -49,7 +49,6 @@
 : i32 IMM $400 or to src ;
 
 \ Writing the thing
-\ TODO: seriously, this is a mess. rework this.
 : disp, disp? if disp c, then ;
 : prefix, ( -- ) exit
   tgt is16? if $66 c, then src isimm? not swap is16? and if $67 c, then ;
@@ -58,15 +57,16 @@
 : modrm1, ( reg op -- ) \ modrm op with 1 argument
   prefix, op, ( reg ) 3 lshift tgtid tgt mod or or ( modrm ) c,
   disp? if disp c, then asm$ ;
+: modrm<imm, ( imm immreg op -- ) \ immediate src, modrm tgt
+  op, 3 lshift tgtid or tgt mod or ( modrm ) c, , disp, asm$ ;
 : modrm2, ( imm? reg op -- ) \ modrm op with 2 arguments
-  prefix,
-  isimm? not if src mod $c0 = not if
+  src mod $c0 = not if
     \ surprise! it's not tgt that is the mod rm, it's src. We're in "alternate"
     \ mode and op is +2.
-    2 + c, ( src ) mod tgt 3 lshift or srcid or ( modrm ) c,
-    disp, asm$ exit then then
-  c, 3 lshift tgtid or tgt mod or ( modrm ) c,
-  isimm? if , then disp, asm$ ;
+    2 + c, ( src ) mod tgt 3 lshift or srcid or
+  else
+    c, 3 lshift tgtid or tgt mod or then
+  ( modrm ) c, disp, asm$ ;
 
 \ operations
 \ Inherent
@@ -85,10 +85,10 @@ $00e9 op jmp,      $0f84 op jz,        $0f85 op jnz,
 
 \ Two operands
 : op ( immop immreg regop -- ) doer c, c, c, does> ( imm? a -- )
+  prefix,
   isimm? if
-    dup 1+ c@ ( immreg ) swap 2 + c@ ( immreg immop ) else
-    c@ src swap ( reg regop ) then
-  modrm2, ;
+    dup 1+ c@ ( immreg ) swap 2 + c@ ( immreg immop ) modrm<imm, else
+    c@ src swap ( reg regop ) modrm2, then ;
 $81 0 $01 op add,  $81 7 $39 op cmp,   $81 5 29 op sub,    $f7 0 $85 op test,
 
 \ tgt or-ed in
@@ -96,6 +96,7 @@ $81 0 $01 op add,  $81 7 $39 op cmp,   $81 5 29 op sub,    $f7 0 $85 op test,
 $58 op pop,        $50 op push,
 
 \ Special
-: mov, isimm? if
-    prefix, $b8 tgtid or c, , asm$ else
+: mov,
+  prefix, isimm? if
+    $b8 tgtid or c, , asm$ else
     src $89 modrm2, then ;