From a9bcbc894ba1ebb9ac6bb203efb3d95567074f87 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maja=20K=C4=85dzio=C5=82ka?= <maya@compilercrim.es>
Date: Thu, 13 Apr 2023 19:11:31 +0200
Subject: [PATCH] Move >IN to 7d00, saving 5 bytes.

---
 README.md            |  6 +++---
 blocks/bootstrap.fth |  2 +-
 boot.s               | 16 +++++++++-------
 3 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/README.md b/README.md
index 578059f..238c601 100644
--- a/README.md
+++ b/README.md
@@ -99,7 +99,7 @@ Due to space constraints, variables such as `STATE` or `BASE` couldn't be expose
 separate words. Depending on the variable, the address is either hardcoded or pushed onto
 the stack on boot:
 
- - `>IN` is a word at `0xa02`. It stores the pointer to the first unparsed character
+ - `>IN` is a word at `0x7d00`. It stores the pointer to the first unparsed character
    of the null-terminated input buffer.
  - The stack on boot is `LATEST STATE BASE HERE #DISK` (with `#DISK` on top).
  - `STATE` has a non-standard format - it is a byte, where `0` means compiling,
@@ -181,8 +181,8 @@ Git or GitHub's web interface. This disparity is handled by two Python scripts:
 
 ## Free bytes
 
-At this moment, not counting the `55 AA` signature at the end, **450** bytes are used,
-leaving 60 bytes for any potential improvements.
+At this moment, not counting the `55 AA` signature at the end, **445** bytes are used,
+leaving 65 bytes for any potential improvements.
 
 Byte saving leaderboard:
  - Ilya Kurdyukov saved 24 bytes. Thanks!
diff --git a/blocks/bootstrap.fth b/blocks/bootstrap.fth
index 4cd6ce8..1be4af1 100644
--- a/blocks/bootstrap.fth
+++ b/blocks/bootstrap.fth
@@ -1,4 +1,4 @@
-: >in a02 ; : run >in ! ;       swap : dp 0 | dup @ 2 - ! | ;
+: >in 7d00 ; : run >in ! ;       swap : dp 0 | dup @ 2 - ! | ;
 : drop  dup -  - ;
 : negate  0 swap - ;            : +  negate - ;
 : here dp @ ;  : cell+ 2 + ;  : cell- 2 - ;  : cells dup + ;
diff --git a/boot.s b/boot.s
index 6bd2998..a8aed2a 100644
--- a/boot.s
+++ b/boot.s
@@ -30,7 +30,9 @@ F_LENMASK   equ 0x1f
 InputBuf equ 0x500
 BlockBuf equ 0x600
 BlockBuf.end equ 0xa00
-InputPtr  equ 0xa02 ; dw
+; we put it at 7d00, since that's in the middle of CompressedData,
+; which we effectively discard before the first access to InputPtr
+InputPtr  equ 0x7d00 ; dw
 RS0 equ 0xb00
 
 SPECIAL_BYTE equ 0xff
@@ -106,7 +108,7 @@ start:
 
 ReadLine:
     mov di, InputBuf
-    mov [InputPtr], di
+    mov [byte bp-BP_POS+InputPtr], di
 .loop:
     mov ah, 0
     int 0x16
@@ -207,7 +209,7 @@ Return:
 ; BX = numeric value
 ; clobbers SI
 ParseWord:
-    mov si, [InputPtr]
+    mov si, [byte bp-BP_POS+InputPtr]
     ; repe scasb would probably save some bytes here if the registers worked out - scasb
     ; uses DI instead of SI :(
 .skiploop:
@@ -231,7 +233,7 @@ ParseWord:
     cbw
     shl bx, 4
     add bx, ax
-    mov [InputPtr], si
+    mov [byte bp-BP_POS+InputPtr], si
     lodsb
     jmp short .takeloop
 
@@ -243,7 +245,7 @@ DiskPacket:
     ; rest is filled out at runtime, overwriting the compressed data,
     ; which isn't necessary anymore
 
-BP_POS equ $
+BP_POS equ $ - $$ + 0x7c00
 
 CompressedData:
     times COMPRESSED_SIZE db 0xcc
@@ -364,7 +366,7 @@ DRIVE_NUMBER equ $+1
 
 ;; Copies the rest of the line to buf.
 defcode LINE, "s:" ; ( buf -- buf+len )
-    xchg si, [InputPtr]
+    xchg si, [byte bp-BP_POS+InputPtr]
 .copy:
     lodsb
     mov [bx], al
@@ -374,7 +376,7 @@ defcode LINE, "s:" ; ( buf -- buf+len )
 .done:
     dec bx
     dec si
-    xchg si, [InputPtr]
+    xchg si, [byte bp-BP_POS+InputPtr]
 
 defcode SWITCH, "|", F_IMMEDIATE
     xor byte[byte bp-BP_POS+STATE], 1