forth: implement "0b" number parsing

forth/parse.fs

@@ -27,7 +27,7 @@
 : (parseh)          ( a -- n f )
     ( '0': ASCII 0x30 'x': 0x78 0x7830: 30768 )
     DUP @ 30768 = NOT IF 0 EXIT THEN    ( a 0 )
-    ( We have "0x" suffix )
+    ( We have "0x" prefix )
     2 +
     ( validate slen )
     DUP SLEN                            ( a l )
@@ -44,9 +44,40 @@
     AGAIN
 ;
 
+( returns negative value on error )
+: bindig            ( c -- n )
+    ( '0' is ASCII 48 )
+    48 -
+    DUP 0 < IF EXIT THEN                ( bad )
+    DUP 2 < IF EXIT THEN                ( good )
+    ( bad )
+    255 -
+;
+
+: (parseb)          ( a -- n f )
+    ( '0': ASCII 0x30 'b': 0x62 0x6230: 25136 )
+    DUP @ 25136 = NOT IF 0 EXIT THEN    ( a 0 )
+    ( We have "0b" prefix )
+    2 +
+    ( validate slen )
+    DUP SLEN                            ( a l )
+    DUP 0 = IF DROP 0 EXIT THEN         ( a 0 )
+    16 > IF DROP 0 EXIT THEN            ( a 0 )
+    0 ( a r )
+    BEGIN
+    OVER C@
+    DUP 0 = IF DROP SWAP DROP 1 EXIT THEN ( r, 1 )
+    bindig                              ( a r n )
+    DUP 0 < IF DROP DROP 1 EXIT THEN    ( a 0 )
+    SWAP 2 * +                          ( a r*2+n )
+    SWAP 1 + SWAP                       ( a+1 r )
+    AGAIN
+;
+
 : (parse)           ( a -- n )
     (parsec) NOT SKIP? EXIT
     (parseh) NOT SKIP? EXIT
+    (parseb) NOT SKIP? EXIT
     (parsed) NOT SKIP? EXIT
     ( nothing works )
     ABORT" unknown word! "

tests/forth/test_parse.fs

@@ -0,0 +1,2 @@
+'b' 0x62 #eq
+0b1111010101 981 #eq