__0a96 → last_file_buffer_byte

edlin.asm

@@ -236,7 +236,9 @@ setup_file_parameters: ; 01ec
 
 	movw r_dx, r_cx
 	add dx, file_buffer
-	mov [__0a96], dx
+	; File buffer is actually 1 byte more than we load from the file
+	; This is because we always place a ^Z after file contents
+	mov [last_file_buffer_byte], dx
 
 read_file:
 	mov dx, psp_fcb_1
@@ -249,7 +251,7 @@ read_file:
 initialize_editor: ; 0240
 	cld
 
-	; Put ^Z at the end of the file in memory
+	; Place ^Z after the end of file in memory
 	mov byte [di], 0x1a ; ^Z
 
 	mov [__0a9a], di
@@ -422,6 +424,12 @@ command_addresses: ; 034a
 	dw command_w ; W
 	dw command_q ; Q
 
+; in:
+;  di = buffer
+;  cx = size of buffer
+; out:
+;  cx = size of buffer upto and including the ^Z, or original passed size
+;  equals (zero) flag = was there a ^Z
 find_file_end_char: ; 035e
 	push di
 	push cx
@@ -449,7 +457,7 @@ command_a: ; 0370
 	cmp word [__0a80], 0
 	jnz __0388
 
-	cmp dx, [__0a96]
+	cmp dx, [last_file_buffer_byte]
 	jnb find_file_end_char.ret
 
 __0388:
@@ -479,10 +487,10 @@ __03ab:
 
 	movw r_ax, r_di
 	addw r_ax, r_cx
-	cmp ax, [__0a96]
+	cmp ax, [last_file_buffer_byte]
 	jna __03ca
 
-	mov di, [__0a96]
+	mov di, [last_file_buffer_byte]
 	movw r_cx, r_ax
 	subw r_cx, r_di
 	mov bx, 1
@@ -1377,7 +1385,7 @@ current_line resw 1 ; 0a90
 __0a92 resw 1
 
 __0a94 resw 1
-__0a96 resw 1
+last_file_buffer_byte resw 1 ; 0a96
 last_valid_address resw 1 ; 0a98
 
 __0a9a resw 1