; The source reader: characters out of a file of any size. ; ; Everything else in the assembler sits on this, so it is the first thing built and the ; thing most worth getting right. It hands out one character at a time and keeps a line ; number, which is what lets an error say where it happened rather than only what it was. ; ; A FILE IS NEVER HELD WHOLE. It arrives a block at a time through osFileBlock, into one ; buffer of 256 bytes, and is fetched again when the buffer runs out. That is why the ; assembler can read a source file bigger than the memory it runs in - which cosmos.asm, ; at 56,047 bytes, already is. ; ; The file is read TWICE, once per pass, and srcRewind is how the second pass starts over. ; Nothing is kept between the passes but the label table. ; ; ---- A stack of readers ---- ; ; #Include splices another file in where it stands, so the reader is a stack: srcInclude ; puts the current file's whole state aside, opens the new one, and the end of that file ; pops the old one back and carries on where it left off. Everything above works on "the ; current file" and does not know the stack is there. ; ; THE WHOLE STATE GOES ASIDE, buffer and all, 293 bytes of it. Keeping only the position ; and re-reading the block on the way back would be cheaper in memory and would cost a disk ; read per pop; at six levels of nesting the copy costs less than the arithmetic to avoid it. ; The buffer pointer survives the trip because it points into the buffer, which is always at ; the same address - the state is saved from and restored to the same variables. ; ; A FILE IS INCLUDED ONCE. Including it twice is not an error, it just does nothing, which ; is what lets two libraries depend on a third. The names are remembered for the length of ; one pass and forgotten between them, because the second pass has to walk exactly the same ; tree the first one did. ; ; Written by Anachronaut #Program ; Opens the file DP0 names. Q is zero if it is there. ; ; The name is copied rather than pointed at, because the caller's copy is in the caller's ; memory and every later block read has to name the file again - there being no such thing ; as an open file to hold on to. srcOpen: SETD.1 SrcTopName CALL srcKeepName ; Kept apart, so that each pass can open it again. CALL srcRestart RET ; Back to the top of the tree: the first file, no includes taken yet, nothing on the stack. ; This is what starts each pass. srcRestart: RSTA SETD.0 SrcDepth STA.0 SETD.0 IncCount STA.0 SETD.0 SrcTopName SETD.1 SrcName CALL srcKeepName CALL srcRewind RET ; Back to the first character, for the second pass. srcRewind: SETD.0 SrcIndex CALL numZero SETD.0 SrcAt CALL numZero SETD.0 SrcCount CALL numZero RSTA SETD.0 SrcEnded STA.0 ; The line number counts from one, the way an editor does. SETD.0 SrcLine CALL numZero SETD.0 SrcLine CALL numStep ; Ask how big it is, which is both the answer to "is it there" and the thing that says ; when to stop asking for blocks. SETD.0 SrcName SWI osFileInfo BNQ srcRewindNo PSHD.3 POPB POPA SETD.0 SrcBlocks STA.0 INCD.0 STB.0 RSTA RSTB CCF ADD ; Q is zero: it is there. RET srcRewindNo: INIA 0d1 SETD.0 SrcEnded STA.0 RSTA INIB 0d1 CCF ADD ; Q is not zero: it is not. RET ; The next character of the file, into SrcChar. Q is zero if there was one, and something ; else at the end of the file. srcNext: SETD.0 SrcEnded LDA.0 BNA srcAtEnd ; Is the buffer used up? SrcAt counts how far into it we have read and SrcCount how many ; of its bytes are the file's, which is 256 for every block but a short last one. SETD.0 SrcAt SETD.2 SrcCount CALL numCompare BNQ srcHaveByte CALL srcLoad BNQ srcAtEnd srcHaveByte: SETD.1 SrcPointer LDD.0.1 LDA.0 INCD.0 STD.0.1 SETD.0 SrcChar STA.0 SETD.0 SrcAt CALL numStep ; A newline is what makes the next character part of the next line. Counting it here, ; as it is handed out, means the line number always describes the character just given. SETD.0 SrcChar LDA.0 INIB 0x0A XOR BNQ srcNextDone SETD.0 SrcLine CALL numStep srcNextDone: RSTA RSTB CCF ADD ; Q is zero: there was a character. RET srcAtEnd: ; This file is finished. If it was included by another, that one is not: it goes back on ; and the next character comes from where it left off, which is what makes an include ; read as though the text had been written there. INIA 0d1 SETD.0 SrcEnded STA.0 SETD.0 SrcDepth LDA.0 BRA srcNothingLeft CALL srcPop BRI srcNext srcNothingLeft: RSTA INIB 0d1 CCF ADD ; Q is not zero: there is no more source anywhere. RET ; ---- The stack ---- ; Opens the file named at DP0 as though its text were written here. Q is zero if the ; reader is now inside it, or if it had already been included and there is nothing to do. srcInclude: SETD.1 IncWanted CALL srcKeepName CALL srcSeenAlready BRQ srcIncludeSkip SETD.0 SrcDepth LDA.0 SETD.2 SrcDepthLimit LDB.2 CCF SUB BNC srcTooDeep CALL srcRemember CALL srcPush ; TWO PLACES, TRIED IN ORDER: where you are, and then /Lib. The same rule the shell uses ; for a program it does not recognise, which is where it came from - a name means the ; one beside you if there is one, and the system's otherwise. ; ; It is what a search path is for, and the host assembler has had one since before there ; was a machine to run this on. Without it every source that calls a service has to sit ; in the same directory as services.asm, and the disk cannot be organised at all. SETD.0 IncWanted SETD.1 SrcName CALL srcKeepName CALL srcRewind BRQ srcIncludeIn CALL srcInLibrary CALL srcRewind BNQ srcIncludeGone srcIncludeIn: RET ; Q is zero, out of srcRewind. ; SrcName becomes the same name inside the library directory. Built here rather than kept ; as a second buffer, because what has to survive is the name the file was ASKED for - ; that is what the include-once list holds, and a file found in the library on one line ; and beside you on another is still the same include. srcInLibrary: SETD.0 SrcLibrary SETD.1 SrcName srcLibraryPrefix: LDA.0 BRA srcLibraryName STA.1 INCD.0 INCD.1 BRI srcLibraryPrefix srcLibraryName: SETD.0 IncWanted srcLibraryCopy: LDA.0 STA.1 BRA srcLibraryDone INCD.0 INCD.1 BRI srcLibraryCopy srcLibraryDone: RET srcIncludeSkip: RSTA RSTB CCF ADD ; Already in, so this line does nothing at all. RET srcIncludeGone: ; ---- Say which one ---- ; ; It said nothing at all, and the assembler's catch-all then said "nothing was written" - ; which is true and useless. Three programs on the disk could be read and not assembled, ; and finding out why meant reading the assembler rather than the message. ; ; SrcName holds the library path by now, because that was the second place tried, so this ; says where it looked as well as what for. Both are worth having: a name that is not in ; /Lib and not beside you is usually one or the other spelt wrong. SETD.0 GoneText SWI osPrintString SETD.0 IncWanted SWI osPrintString SETD.0 GoneWhereText SWI osPrintString SETD.0 SrcName SWI osPrintString SETD.0 GoneEndText SWI osPrintString ; The file is not there. The stack is left as it is: the caller stops the assembly, and ; unwinding for the sake of tidiness would only hide where it happened. RSTA INIB 0d1 CCF ADD RET srcTooDeep: SETD.0 TooDeepText SWI osPrintString RSTA INIB 0d1 CCF ADD RET ; Puts the current file aside and makes room for another. srcPush: CALL srcSlot SETD.0 SrcState SETD.1 SrcSlot LDD.1.1 CALL srcCopyState SETD.0 SrcDepth LDA.0 INCA STA.0 RET ; And takes it back. srcPop: SETD.0 SrcDepth LDA.0 DECA STA.0 CALL srcSlot SETD.1 SrcSlot LDD.0.1 SETD.1 SrcState CALL srcCopyState RET ; Puts one character back, so that the next read produces it again. The character itself ; is in A, because whether it was a newline decides whether a line goes back too. ; ; The tokenizer holds one character of lookahead, and at an #Include that character belongs ; to the file about to be put aside. Undoing the read is how it stays with that file: when ; the file is opened again the character is simply still there, and nothing has to be ; carried across the include or handed back at some moment chosen by the reader. ; ; CARRYING IT ACROSS WAS THE OBVIOUS THING AND IT WAS WRONG. A file runs out in the middle ; of whatever the tokenizer happens to be doing, so handing the character back then injects ; it into the middle of a word: `start:` came back as `s` and then `tart:`, which assembles ; into a file that looks entirely reasonable. srcStepBack: INIB 0x0A XOR BNQ srcStepBackAt SETD.0 SrcLine SETD.2 SrcOne CALL numTake ; A newline not yet read has not started a line either. srcStepBackAt: SETD.0 SrcAt SETD.2 SrcOne CALL numTake SETD.0 SrcPointer SETD.2 SrcOne CALL numTake RET ; Where the slot for the current depth is, into SrcSlot. srcSlot: SETD.0 SrcSlot SETD.2 ScratchSrcStack CALL numSet ; WHERE the stack is, not what is in it. SETD.0 SrcSlotLeft SETD.2 SrcDepth LDA.2 STA.0 srcSlotLoop: SETD.0 SrcSlotLeft LDA.0 BRA srcSlotDone DECA STA.0 SETD.0 SrcSlot SETD.2 SrcStateBytes CALL numAdd BRI srcSlotLoop srcSlotDone: RET ; The whole reader state, from DP0 to DP1. srcCopyState: SETD.2 SrcCopyFrom STD.0.2 SETD.2 SrcCopyTo STD.1.2 SETD.0 SrcCopyLeft SETD.2 SrcStateBytes CALL numSet srcCopyLoop: SETD.1 SrcCopyFrom LDD.0.1 LDA.0 SETD.1 SrcCopyTo LDD.0.1 STA.0 SETD.0 SrcCopyFrom CALL numStep SETD.0 SrcCopyTo CALL numStep SETD.0 SrcCopyLeft SETD.2 SrcOne CALL numTake SETD.0 SrcCopyLeft LDA.0 INCD.0 LDB.0 OR BNQ srcCopyLoop RET ; ---- Which files have been in ---- ; Q is zero if IncWanted has already been included in this pass. srcSeenAlready: RSTA SETD.0 IncLeft STA.0 srcSeenLoop: SETD.0 IncLeft LDA.0 SETD.2 IncCount LDB.2 CCF SUB BRQ srcSeenNo CALL srcSeenSlot SETD.1 IncSlot LDD.0.1 SETD.1 IncWanted CALL sameText BRQ srcSeenYes SETD.0 IncLeft LDA.0 INCA STA.0 BRI srcSeenLoop srcSeenYes: RSTA RSTB CCF ADD RET srcSeenNo: RSTA INIB 0d1 CCF ADD RET ; Writes IncWanted down as having been included. srcRemember: SETD.0 IncLeft SETD.2 IncCount LDA.2 STA.0 CALL srcSeenSlot SETD.0 IncWanted SETD.1 IncSlot LDD.1.1 CALL srcKeepName SETD.0 IncCount LDA.0 INCA STA.0 RET ; Where name number IncLeft sits, into IncSlot. Fixed fields of 23 bytes: there are few of ; these and they are short, so an arena would cost more code than it saved. srcSeenSlot: SETD.0 IncSlot SETD.2 ScratchIncNames CALL numSet SETD.0 IncSlotLeft SETD.2 IncLeft LDA.2 STA.0 srcSeenSlotLoop: SETD.0 IncSlotLeft LDA.0 BRA srcSeenSlotDone DECA STA.0 INIA 0d23 SETD.0 IncSlot CALL numAddByte BRI srcSeenSlotLoop srcSeenSlotDone: RET ; Fetches the block SrcIndex names, and steps SrcIndex past it. Q is zero if there was one. ; ; Running off the end is not a failure here: osFileBlock answers three for a block past the ; end of the file, which is how a reader finds out it has finished. Any other refusal is a ; real one, and both come back the same way because there is nothing useful to do about ; either except stop. srcLoad: SETD.0 SrcName SETD.1 SrcBuffer SETD.2 SrcIndex LDA.2 INCD.2 LDB.2 SWI osFileBlock BNQ srcLoadNo ; DP3 says how many of the block's bytes belong to the file: a whole 256 except in a ; short last one, which is why it comes back in a pointer and not a register. PSHD.3 POPB POPA SETD.0 SrcCount STA.0 INCD.0 STB.0 SETD.0 SrcAt CALL numZero SETD.0 SrcIndex CALL numStep ; The walking pointer starts at the front of the buffer again. SETD.0 SrcBuffer SETD.1 SrcPointer STD.0.1 RSTA RSTB CCF ADD RET srcLoadNo: RSTA INIB 0d1 CCF ADD RET ; Copies the name at DP0 into DP1, up to 22 characters of it and the zero after them, ; which is as long as a name on this filesystem may be. srcKeepName: INIA 0d22 SETD.2 SrcLeft STA.2 srcKeepLoop: LDA.0 BRA srcKeepEnd STA.1 INCD.0 INCD.1 LDA.2 DECA STA.2 BNA srcKeepLoop srcKeepEnd: RSTA STA.1 ; The zero that makes it a string. RET #Data ; ---- The current file, as one block so that it can be put aside in one piece ---- ; SrcState: ; THIRTY TWO RATHER THAN THE TWENTY THREE A NAME NEEDS, because what goes here is a PATH: ; an include not found beside you is looked for in the library, and "/Lib/" plus a name of ; twenty two plus the zero that ends it is twenty eight. Every block of the file is asked ; for by this name, so it has to be the one that resolves, not the one that was typed. SrcName: #Reserve 0d32 SrcBlocks: 0x00 0x00 SrcIndex: 0x00 0x00 SrcCount: 0x00 0x00 SrcAt: 0x00 0x00 SrcLine: 0x00 0x00 SrcPointer: 0x00 0x00 SrcEnded: 0x00 ; One block, which is the whole of what a source file costs in memory however big it is. SrcBuffer: #Reserve 0d256 ; 301 bytes: a name of 32, six numbers of two, one single byte, and the buffer. NOTHING MAY ; BE ADDED IN THE MIDDLE OF THE BLOCK ABOVE without changing this to match, and the room ; set aside for six of them in scratch.asm has to be at least six times it. SrcStateBytes: 0x01 0x2D SrcDepthLimit: 0d6 ; Where an include is looked for when it is not beside you. One fixed place rather than a ; list somebody sets, for the same reason the shell has one fixed place for programs: a ; list would need somewhere to live between one boot and the next. SrcLibrary: "/Lib/" SrcOne: 0x00 0x01 SrcChar: 0x00 SrcLeft: 0x00 SrcDepth: 0x00 SrcSlot: 0x00 0x00 SrcSlotLeft: 0x00 SrcCopyFrom: 0x00 0x00 SrcCopyTo: 0x00 0x00 SrcCopyLeft: 0x00 0x00 ; The file the assembly started from, so that each pass can open it again. SrcTopName: #Reserve 0d23 IncWanted: #Reserve 0d23 IncCount: 0x00 IncLeft: 0x00 IncSlot: 0x00 0x00 IncSlotLeft: 0x00 GoneText: "cannot find " GoneWhereText: ", not beside the file that asked and not as " GoneEndText: " " TooDeepText: "included files are nested deeper than this assembler will follow "