SplitBit assembles SplitBit: M1, a single file with no includes

Programs/CosmOS/Assembler/ is an assembler written in SplitBit assembly. It
runs under CosmOS, reads source off a SplitBit disk, and writes a binary back
to it with no host involved anywhere:

    > run Asm.sbx hello.asm
    wrote hello.bin: program 17, data 14, labels 2

THE ACCEPTANCE TEST IS THE BYTES. Tests/native.sh assembles Programs/hello.asm
both ways and compares the two files byte for byte, then runs the one the
machine built. "It ran" and "the sizes look right" both pass for a binary with
a label one byte out, which is a program that jumps into the middle of an
instruction - so the only honest test is the one SplitDisk and sbfs.asm
already work under: two implementations of one written specification, each
checking the other. The files are identical and the result prints Hello,
World! in 70 cycles.

hello.asm is the target because it is the oldest program in the repository.
The first thing this machine ever ran is now the first thing it assembles for
itself.

TWO PASSES OVER STREAMED SOURCE. The C assembler reads every token of every
file into one array; that cannot port, because cosmos.asm alone is 56,047
bytes against 64K of Data Memory. The native one streams through a 256 byte
window, twice, and keeps only the label table between the passes. Two passes
suffice because every length is known without resolving anything - an
instruction's from its shape, a value's is one, a string's is its characters
and a zero - so the first pass fixes every address and the second never needs
a fixup list. A forward reference stops being a special case and becomes the
reason there are two passes at all.

The parts, each checked before anything was built on it:
  source.asm    characters out of a file of any size, with a line number
  token.asm     tokens out of characters, one character of lookahead
  classify.asm  what a token is, in the C assembler's order, which IS the
                language: keyword, instruction, value, string, label
  labels.asm    names packed in an arena, four bytes of index each
  numbers.asm   sixteen bit arithmetic, since sbfs.asm's cannot be reached
  table.asm     the instruction set, generated by the same script the
                monitor's copy is, and now BOTH are checked by docs.sh

readTest.asm and tokenTest.asm check the reader and the tokenizer on their
own, recorded as cosmosSource and cosmosTokens. A wrong classification does
not produce a wrong byte somewhere obvious; it produces a right looking
program of the wrong length, so it is worth catching where it happens.

WHAT IT REFUSES: #Include, #Base, #Align, #Reserve and #Vectors are refused
by name rather than ignored. Skipping a directive would produce a file that
looked right and was the wrong length, which is the worst thing an assembler
can do.

Two traps worth recording, both already known to this project and both hit
again: CALL restores A, B and DP0-DP2, so three routines returning an answer
in A had it undone by their own return; and numStep works on DP0, so three
sites that set DP1 left a pointer that never advanced.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW

Programs/CosmOS/Assembler/readTest.asm

@@ -0,0 +1,84 @@
+; The source reader on its own, before anything is built on top of it.
+;
+; Everything else in the assembler reads its source through srcNext, so a fault in here
+; would turn up later as a mysterious wrong byte in an output file. It is worth checking by
+; itself, against a file whose contents are already known.
+;
+; It reads whatever it was told to, prints every character back, and then says how many
+; lines went past. The file it is given is deliberately bigger than one block, so the seam
+; between one block and the next is crossed rather than assumed.
+;
+; Written by Anachronaut
+
+#Include services.asm
+
+#Program
+
+  #Base 0x2000
+
+start:
+  SETD.0 Wanted
+  INIB 0d23
+  SWI osArgument
+  SETD.0 Wanted
+  LDA.0
+  BRA nothingAsked
+
+  SETD.0 Wanted
+  CALL srcOpen
+  BNQ noFile
+
+readLoop:
+  CALL srcNext
+  BNQ readDone
+  SETD.0 SrcChar
+  LDA.0
+  OUTA 0x00                 ; Straight to the console: one character is not a string.
+  BRI readLoop
+
+readDone:
+  SETD.0 LinesText
+  SWI osPrintString
+  SETD.0 SrcLine
+  LDA.0
+  INCD.0
+  LDB.0
+  SWI osPrintNumber
+  SETD.0 NewLine
+  SWI osPrintString
+  SWI osExit
+
+nothingAsked:
+  SETD.0 AskText
+  SWI osPrintString
+  SWI osExit
+
+noFile:
+  SETD.0 NoFileText
+  SWI osPrintString
+  SWI osExit
+
+#Data
+
+  #Base 0x1000
+
+Wanted:
+  #Reserve 0d23
+
+LinesText:
+"---- lines: "
+NewLine:
+"
+"
+AskText:
+"say which file
+"
+NoFileText:
+"no such file
+"
+
+; The libraries go last, after both segments have been based. An included file that carries
+; code brings its own #Program and #Data lines with it, and a #Base has to come before
+; anything is in the segment it bases - so the bases are set here and the code arrives after.
+#Include numbers.asm
+#Include source.asm